BENDIX AD-SP SYSTEM PURGE AIR DRYER User manual

1
®
SD-08-2415
Bendix®AD-SP™System Purge Air Dryer & SC-PR™
Single Check Protection Valve
“SPIN OFF”
DESICCANT
CARTRIDGE
EXHAUST PORT
MOUNTING
HOLES (3)
AD-SP™air dryer aluminum body contains the following
serviceable components or assemblies; the turbocharger
cut-offvalve,heaterandthermostatassembly,deliverycheck
valve assembly and combined purge and relief valve
assembly. In addition, the non-serviceable purge control
valve is located in the body. All service and replacement
canbe accomplishedfrom theexteriorof thedryer without
removal from the vehicle. The spin-on desiccant cartridge
isremoved and installed usinga “strap wrench.”
The AD-SP™air dryer has three female pipe thread air
connectionsidentified as follows:
Air Connection Port ID Function/Connection
CON 4...................... ControlPort (purgevalvecontrol
&turbo cut-off).
SUP 11 .................... Supply Port (air in).
DEL 2 ...................... Delivery Port(air out).
DESCRIPTION
The function of the AD-SP™System Purge Air Dryer is to
collect and remove air system contaminants in solid, liquid
andvaporformbeforetheyenterthebrakesystem.Itprovides
clean,dry airto the componentsof thebrake systemwhich
increases the life of the system and reduces maintenance
costs.Daily manualdraining ofthe reservoirsis eliminated.
The system purge designation is used because the
AD-SP™airdryerusesasmallportion ofsystemairpressure
fromthe supplyand frontaxle servicereservoirs toperform
thepurgeor regenerativefunction.AnSC-PR™singlecheck
protectionvalve oravalve thatperforms thesame function
is always used in conjunction with theAD-SP™air dryer to
protect the service system.
The AD-SP™air dryer consists of two major component
groups, a spin off desiccant cartridge assembly and a die
cast aluminum body assembly. The desiccant cartridge is
self contained and serviced as a complete assembly.The
FIGURE 1 - AD-SP™SYSTEM PURGE AIR DRYER
DELIVERY PORT
EXHAUST PORT
SUPPLY
PORT
MOUNTING
HOLES (3)
TURBO
CUTOFF VALVE
HEATER &
THERMOSTAT
CONNECTOR
CONTROL
PORT

2
After exiting the end cover, the air flows into the desiccant
cartridgewhere anoil separator,located betweenthe outer
and inner shells of the cartridge, removes water in liquid
form as well as liquid oil and solid contaminants.
Afterexitingthe oil separator, airenters thespacebetween
the desiccant drying bed and the outer cartridge shell and
flowsdownthroughthecolumnofdesiccant.Flowingthrough
the desiccant column, air becomes progressively dryer as
watervapor adheres tothe desiccantmaterial in aprocess
knownas “ADSORPTION.” Usingthe adsorption process,
thedesiccant cartridge typicallyremoves 95% ofthe water
vaporfrom thepressurized air.
Dry air exits the bottom of the desiccant cartridge through
its center opening and returns to the air dryer body
assembly. As air flows through the supply cavity it is also
conducted, via internal passages, to the non-serviceable
purgecontrol mechanismcontained inthe body.The purge
control mechanism (not shown) is able to monitor supply
airpressure. The air thenflows through thedeliverycheck
valveassembly andoutthe deliveryport tothe first(supply)
reservoir of the air system.As air moves past the delivery
check valve, on its way to the delivery port, it is also
conducted to the purge control mechanism. The purge
control mechanism is able to monitor air brake system
pressure as well as supply air pressure.
FIGURE 2 - AD-SP™AIR DRYER SYSTEM DRAWING WITH EXTERIOR AND TOP VIEW OF SC-PR™VALVE.
FRONT AXLE
AD-SP™
AIR
DRYER
COMPRESSOR
GOVERNOR
REAR AXLE
SUPPLY SC-PR™
VALVE
DELIVERY PORT
(TO FRONT SERVICE
RESERVOIR)
EMBOSSED PORT
IDENTIFICATION “2 DEL” EMBOSSED PORT
IDENTIFICATION
“1 SUP”
SUPPLY PORT
(FROM SUPPLY
RESERVOIR)
OPERATION
GENERAL
TheAD-SP™air dryer alternates between two operational
modes or “cycles”during operation: the ChargeCycle and
the Purge Cycle. The following description of operation is
separated into these “cycles” of operation.
CHARGE CYCLE (refer to Figure 3)
When the compressor is loaded (compressing air)
compressed air, along with oil, oil vapor, water and water
vapor flows through the compressor discharge line to the
supply port of the air dryer body.
Air entering the supply port immediately encounters the
“turbocut-off” valve.Withno airpressure inthecontrol port,
theturbo cut-off piston movesthe valve awayfrom its seat
in the body allowing the supply air to enter the body.As air
travelsthrough theend coverassembly,its directionof flow
changesseveral times, reducingthe temperature,causing
contaminantsto condense anddrop tothe bottom orsump
of the air dryer body.

3
FIGURE 4 - AD-SP™AIR DRYER RELIEF VALVE OPERATION
DESICCANT
OIL
SEPARATOR DELIVERY
CHECK
DELIVERY
PORT
TURBO
CUTOFF
CONTROL
PORT
GOVERNOR
COMPRESSOR
PURGE /
RELIEF
VALVE
FRONT
RESERVOIR
SC-PR™
VALVE
REAR
RESERVOIR
ENGINE
TURBO
PURGE
PISTON
EXHAUST
PORT
SUPPLY
PORT
PURGE
ORIFICE
FIGURE 3 - AD-SP™AIR DRYER CHARGE CYCLE
DESICCANT
OIL
SEPARATOR DELIVERY
CHECK
DELIVERY
PORT
TURBO
CUTOFF
CONTROL
PORT
MALFUNCTIONING
GOVERNOR
COMPRESSOR
PURGE /
RELIEF
VALVE
FRONT
RESERVOIR
SC-PR™
VALVE
REAR
RESERVOIR
ENGINE
TURBO EXHAUST
PORT
SUPPLY
PORT
PURGE
ORIFICE
The air dryer will remain in the charge cycle until the air
brakesystempressure buildstothegovernor cutoutsetting.
To protect against over pressurization of the AD-SP™air
dryer, the purge valve incorporates an integral relief valve
feature. In the event that the compressor unloader
mechanismorgovernor malfunctions,atapproximately 200
psi supply air pressure theAD-SP™air dryer purge valve
will open (without control pressure), and vent excess air
pressureto atmosphere (referto Figure 4).
PURGE
PISTON

4
DESICCANT
OIL
SEPARATOR DELIVERY
CHECK
DELIVERY
PORT
CONTROL
PORT
COMPRESSOR
PURGE /
RELIEF
VALVE
FRONT
RESERVOIR
SC-PR™
VALVE
REAR
RESERVOIR
ENGINE
TURBO
PURGE
ORIFICE
EXHAUST
PORT
TURBO
CUTOFF
GOVERNOR
FIGURE 5 - AD-SP™AIR DRYER PURGE CYCLE
PURGE CYCLE (refer to Figure 5)
Whenair brakesystem pressurereachesthe cutoutsetting
of the governor, typically 120 psi, the compressor unloads
(aircompressionis stopped) andthe purge cycle ofthe air
dryerbegins. When thegovernor unloadsthe compressor,
it pressurizes the compressor unloader mechanism and
thelineconnecting thegovernorunloader porttothe control
port of theAD-SP™air dryer body. Air entering the control
port is simultaneously directed to the turbo cut-off valve
andthe purgevalve control piston.
The initial purge cycle consists of two simultaneous
occurrences; the closing of the turbo cut-off valve and the
openingof thepurge valve.Each isdiscussed belowunder
aseparate subheading.
TURBO CUT-OFF VALVE (refer to Figure 5)
Theprimary function ofthe turbo cut-offvalve is toprevent
loss of engine turbocharger air pressure through the
AD-SP™airdryer in systemswhere the compressorintake
is connected to the engine turbocharger. The turbo cut-off
valve also eliminates the “puffing” of air out the open air
dryer exhaust when a naturally aspirated, single cylinder
compressorisequipped with aninlet check valve.
Governorunloader pressurecauses the turbocut-off valve
pistontomoveandclose. Withtheturbo cut-offvalvepiston
seated (closed position), air in the discharge line and
AD-SP™air dryer inlet port is prevented from entering the
airdryer.
PURGE PISTON
TheAD-SP™airdryerpurge pistonalso movesin response
togovernor unloader pressure, causingthe purge valveto
open to atmosphere. Contaminants in the body sump are
instantly expelled when the purge valve opens.Air which
was flowing through the desiccant cartridge immediately
changesdirection andbegins toflowback towardthe open
purgevalve. Oilandsolid contaminantscollected bythe oil
separator are removed by air flowing from the desiccant
dryingbed tothe openpurgevalve.
DESICCANT RE-ACTIVATION (DRYING THE
DESICCANT)
The initial decompression of the air dryer assembly lasts
onlya fewseconds and isevidenced byan audibleburst of
air at the AD-SP™air dryer exhaust. The initial
decompression of the air dryer assembly is “sensed” by
the purge control mechanism and is used by the purge
mechanismas a signal thatdesiccant re-activation should
begin. The purge control mechanism “remembers” the
highest pressure attained in the air system, the cutout
pressureof thegovernor.
Theactual re-activation ofthe desiccantdrying bed begins
as the purge mechanism allows dry air to flow from the
delivery port (air brake system) back into the AD-SP™air
dryerbodyandthroughthedesiccantcartridge.Thedelivery
check valve assembly prevents air pressure in the brake
system from returning to the air dryer and flowing out the
openpurge valve. The deliverycheck valve forcessystem
PURGE
PISTON
SUPPLY
RESERVOIR

5
air to flow through the purge mechanism. Dry air for the
brakesystem entersthe purge controlmechanism through
anairchannellocatedinthe deliveryport,beforethedelivery
single check valve. It flows through the mechanism and
exitsa purge orifice;its pressure islowered and itsvolume
increased. The flow of dry air through the drying bed
reactivates the desiccant material by removing the water
vaporadhering toit.
Dry, brake system air will continue to flow through the
desiccant bed until the purge mechanism senses that the
brake system pressure has dropped between 8 - 14 psi
below what it “remembered” as being high (governor cut
out).For example: Ifgovernor cutoutpressure was 120psi
thepurge mechanism willuse air fromthe supply andfront
axlereservoirs untilitdetects thatpressure hasdropped to
between112 -106 psi.System pressure willbe reduced in
the supply and secondary (front axle) reservoirs only. The
primary or rear axle service reservoir will retain governor
cutoutpressure (in theexample, 120 psi).The purge cycle
andre-activation ofthe desiccantdrying bedalong withthe
resulting pressure reduction takes place in approximately
15 - 20 seconds.
Once the purge cycle is complete, the purge control
mechanism closes and no further reduction of system
pressure should occur. The air dryer is ready for the next
charge cycle to begin.
Thepurgevalve willremainopen andtheturbo cut-offvalve
closed after the purge cycle is complete and neither will
changeposition until airbrake system pressureis reduced
togovernor cut-in pressureand the ChargeCycle begins.
SC-PR™VALVE DESCRIPTION
The SC-PR™single check protection valve, combines a
singlecheckvalveandapressureprotectionvalveinasingle
assembly. Itsprimary useis inconjunction withthe Bendix®
AD-SP™air dryer and is installed in the front axle
(secondary)service reservoirin place of a standardsingle
checkvalve.
TheSC-PR™valveallows theAD-SP™air dryerto draw air
pressurefromthefrontaxleservicereservoirduringthepurge
cycle. It also protects the air pressure in the front axle
service reservoir, in the event of a compressor, supply, or
rearaxle reservoir failure,or malfunctionof theAD-SP™air
dryerpurge control mechanism.
The SC-PR™valve is intended for direct mounting to the
service reservoir. Both SC-PR™valve air connections are
1/2 inch pipe thread and each is identified with cast,
embossedletters for easeof identification andinstallation.
Theletter identifications andconnections to theair system
areshown belowfor reference.
DIAPHRAGM
CHARGING
BELOW 100 PSI
SUPPLY
PORT
DELIVERY
PORT
SINGLE
CHECK
VALVE
CHARGING
ABOVE 100 PSI
SUPPLY
PORT
DIAPHRAGM
DELIVERY
PORT
SUPPLY
RESERVOIR
AD-SP™
AIR
DRYER
COMPRESSOR
SC-PR™VALVE
REAR AXLE
RESERVOIR
FRONT AXLE RES.
FIGURE 6 - SC-PR™VALVE CHARGE POSITION*
Air Connection Identification System Connection
Supply .................... 1 SUP ....................... ConnectedtoSupply(wet)
Reservoir
Delivery................. 2 DEL......................... NippleMountedtoFront
Axle Service Reservoir
SC-PR™VALVE OPERATION
CHARGING
During initial air system build up, air flows from the supply
reservoirtothesupply portoftheSC-PR™valve.Airentering
the SC-PR™valve supply port is present beneath the
pressure protection diaphragm and simultaneously flows
through the single check valve portion into the front axle
service reservoir. With supply air pressure less than 100
psi,the pressure protectiondiaphragm, whichfunctions as
avalve,remainsseatedonitsinletduetospringforceabove.
GOVERNOR
*Cutawayviewsarefunctionallycorrect,butdonotrepresentcurrentformofSC-PR™valve.

6
Whensupplypressurereaches100psi,thediaphragmmoves
awayfromitsseatandairenteringthesupplyportflowsthrough
the pressure protection valve portion, as well as the single
checkvalveportion,andintothefrontaxleservicereservoir.
The pressure protection valve remains open as long as
supplypressure remains above95 psi.
PURGING
WhentheAD-SP™airdryer begins itspurge cycle,air from
the supply and front axle service reservoirs flows back to
the air dryer to re-activate the desiccant. Air flowing from
thefront axleservicereservoir tothe supplyreservoir must
passthroughthe SC-PR™pressureprotection valveportion
because the single check valve portion is closed to flow in
that direction.
SinceanAD-SP™air dryerpurge cycle begins atgovernor
cutout (120 psi minimum) and only reduces reservoir air
pressure8- 14 psi,the SC-PR™pressure protection valve
will normally remain open. If a malfunction occurs that
causes the supply reservoir to lose pressure, air from the
front axle service reservoir will flow back to the supply
reservoiruntil the pressure beneaththe SC-PR™pressure
protection valve diaphragm falls to approximately 95 psi.
With 95 psi or less beneath the diaphragm, spring force
moves the diaphragm into contact with the inlet seat and
airflow tothesupply reservoirceases. Thesupplyreservoir
willcontinuetolosepressure,however95psi willberetained
inthe front axleservice reservoirfor braking.
Any malfunction occurring between the compressor and
SC-PR™valve that causes pressure to drop below 95 psi
willresult in the SC-PR™pressure protectionvalve closing
andprotecting the frontaxle servicereservoir.
PREVENTIVE MAINTENANCE
Important: Review the warranty policy before performing
anyintrusivemaintenanceprocedures.Anextendedwarranty
maybe voidedifintrusive maintenanceis performedduring
this period.
Becausenotwovehicles operateunderidenticalconditions,
maintenance and maintenance intervals will vary.
Experience is a valuable guide in determining the best
maintenanceinterval forany oneparticularoperation.
Every 900 operating hours, or 25,000 miles or three (3)
months:
1. Check for moisture in the air brake system by opening
reservoirs,drain cocks,ordrain valvesandchecking for
presenceof water.If moistureis present, thedesiccant
cartridgemayrequirereplacement;however,thefollowing
conditions can also cause water accumulation and
shouldbe consideredbefore replacingthe desiccant:
DIAPHRAGM
SUPPLY
PORT
DELIVERY
PORT
SINGLE
CHECK
VALVE
SUPPLY
PORT
DIAPHRAGM
DELIVERY
PORT
SUPPLY
RESERVOIR
AD-SP™
AIR
DRYER
COMPRESSOR
GOVERNOR
SC-PR™VALVE
REAR AXLE
RESERVOIR
FRONT AXLE RES.
FIGURE 7 - SC-PR™SINGLE CHECK PROTECTION VALVE
PURGE POSITION*
NORMAL PURGE
PROTECTION
FUNCTION
A. An outside air source has been used to charge the
system. This air does not pass through the drying
bed.
B. Airusage isexceptionally high andnot normal fora
highwayvehicle.
Thismay bedue toaccessory airdemandsor some
unusualairrequirementthatdoesnotallowthecom-
pressor to load and unload (compressing and
non-compressingcycle) ina normalfashion. Check
for high air system leakage. If the vehicle vocation
has changed it may be necessary to upgrade the
compressor size. Refer toAppendixA, TableAand
the column entitled Vehicle Vocation.
C. The air dryer has been installed in a system that
has been previously used without an air dryer. The
system will be saturated with moisture and several
weeks of operation may be required to dry it out.
*Cutawayviewsarefunctionallycorrect,butdonotrepresentcurrentformofSC-PR™valve.

7
D. Asinglecheck valve,or adevice witha checkvalve
feature,mayhave been installed tothe inlet port of
the supply tank or in the delivery line between the
air dryer and the supply tank. This will prevent re-
generation of the air dryer desiccant cartridge and
leadtomoisture accumulation intheair reservoirs.
E. Location of the air dryer is too close to the air com-
pressor. Refer to Locating AD-SP™Air Dryer On
Vehicle section andAppendixA, TableA, column 2
fordischarge line length.
F. Inareas wheremorethan a30degree rangeoftem-
peratureoccurs in oneday, small amountsofwater
cantemporarily accumulate inthe airbrake system
due to condensation. Under these conditions, the
presence of small amounts of moisture is normal
and should not be considered as an indication that
thedryer is notpreforming properly.
Note: A small amount of oil in the system is normal and
should not be considered as a reason to replace the
desiccant cartridge; oil-stained desiccant can function
adequately.
2. Visually check for physical damage to the AD-SP™air
dryer such as dented desiccant cartridge, chaffed or
broken air and electrical lines and broken or missing
parts.Check theSC-PR™valvealso.
3. Check mounting bolts for tightness. Re-torque to 50 ft.
pounds.
4. Perform the Operation & Leakage Tests listed in this
publication.
Every 3600 operating hours, or 100,000 miles or twelve
(12)months:
1. TesttheAD-SP™airdryer turbocut-offandpurge valves
forleakage.Disconnectthesupply,controland delivery
linesfromtheAD-SP™air dryer.Performthe testsbelow
inthe order theyare presented.
A. Apply 120 psi shop air pressure to the control port
and a soap solution to the supply port. If leakage
exceeds a 1” bubble in 5 seconds, repair the turbo
cut-offpiston andvalvebefore proceedingto step2.
B. With 120 psi shop air pressure applied to the con-
trolport, apply asoap solutionto the purgeexhaust
port. If leakage exceeds a 1” bubble in 5 seconds,
repairthe purgepistonand valvebefore proceeding
to step 2.
C. With 120 psi shop air pressure applied to the con-
trol and supply port, apply a soap solution to the
purgeexhaust port. If leakageexceeds a 1”bubble
in5seconds,repairtheturbocut-offpistonandvalve
beforeproceeding to step 2.
D. Witha plug installedin the deliveryport,0 psi inthe
control port, and 120 psi applied to the supply port,
apply a soap solution to the purge exhaust port. If
leakage exceeds a 1” bubble in 5 seconds, repair
the purge piston and valve before proceeding to
step 2.
2. Perform the Operation & Leakage Tests shown in this
publication.
Every 10,800 hours; or 350,000 miles or 36 months:
1. Replacethe airdryer desiccant cartridge.
Note:Thedesiccantchangeinterval mayvary fromvehicle
tovehicle.Although typical desiccantcartridge life is three
years, many will perform adequately for a longer period of
time.In order totake maximumadvantage of desiccantlife
andassure that replacementoccurs only whennecessary,
itisimportantthatOperation&Leakage Testsbe performed.
2. Perform the Operation & Leakage Tests shown in this
publication.
WARNING!
This air dryer is intended to remove moisture and other
contaminants normally found in the air brake system.
Do not inject alcohol, anti-freeze, or other de-icing
substances into or upstream of the air dryer. Alcohol
is removed by the dryer, but reduces the effectiveness
of the device to dry air. Use of other substances can
damage the air dryer and may void the warranty.
OPERATION & LEAKAGE TESTS (ALSO SEE
VIDEO BW2327)
1. Check for excessive leakage around the purge valve.
Withthe compressorinloaded mode(compressingair),
apply a soap solution to the purge valve exhaust port
and observe that leakage does not exceed a 1” bubble
in 5 second. If the leakage exceeds the maximum
specified,service thepurgevalve assembly.
2. Checkfor leakagearound thedesiccant cartridge.With
thecompressorinloadedmode (compressingair),apply
asoap solutionaround thedesiccant cartridgesealand
observe that no leakage occurs. If leakage is noted,
tightenthecartridge usingastrap wrenchandre-test for
leakage.
3. While observing the dash gauge(s), build up system
pressureatapproximately1,800engine/compressorrpm
to governor cut-out. Note the pressure on the dash
gauge(s)atthemoment governorcutoutoccursandthat
theAD-SP™air dryer purges with an audible escape of
air.Observe thedashgauge(s)pressurefor twominutes
after the purge cycle begins. The front axle service
(secondary)reservoirpressureshouldnotdropmorethan
8-14psi below thegovernor cutoutpressure noted and
therearaxle(primary)reservoirpressureshouldnotdrop
more than 2 psi. Perform this test 3 times to positively
confirmthe values.

8
A. If the pressure drop in the front axle reservoir ex-
ceeds 8-14 psi, check the air brake system for
excessiveleakage and repair andre-test. If the ex-
cessivepressure droppersists,replace theAD-SP™
airdryer.
B. If the pressure drop in the rear axle reservoir
exceeds 2 psi, check the air brake system for
excessiveleakage andrepair.
Build up system pressure to governor cut-out, wait 30
seconds for completion of the purge cycle, then "Fan"
the service brakes to reduce system air pressure to
governorcut-in. Notethat thesystem onceagain builds
to full pressure and is followed by anAD-SP™air dryer
purge.
4. Check the operation of the SC-PR™single check
protection valve. Build system pressure to governor
cutout,wait30secondsforcompletionofthepurgecycle,
thendrainallair pressurefromthesupplyreservoir while
observingthefrontaxle reservoirdashgauge.Reservoir
pressure should decrease to approximately 95 psi and
stop. If front axle reservoir pressure continues to drop
replace the SC-PR™valve. Do not attempt to adjust
theSC-PR™valve. This valveisfactory presetandmix-
adjustment can result in insufficient air pressure in the
front axle reservoir in the event of a line or component
failure. The rear axle reservoir pressure should remain
constant.
FIGURE 8 - AD-SP™SYSTEM PURGE AIR DRYER EXPLODED VIEW
O-RING
DESICCANT
CARTRIDGE
AD-SP™AIR
DRYER BODY
DELIVERY PORT
SUPPLY PORT
PURGE VALVE
O-RING
PURGE PISTON
SPRING
EXHAUST COVER
RETAINING RING
HEATER & THERMOSTAT
ASSEMBLY
CONNECTOR
RETAINING RING
RETAINING RING CAP
PISTON O-RINGS
CONTROL PORT
5. Check the operation of the heater and thermostat
assembly in the body during cold weather operation (if
possible)as follows:
A. Electric Power to the Heater and Thermostat
With the ignition or engine kill switch in the ON
position, check for voltage to the heater and
thermostatassembly using avoltmeter ortest light.
Unplugtheelectrical connector at theair dryer and
place the test leads on each of the pins of the male
connector. If there is no voltage, look for a blown
fuse.broken wires,or corrosioninthe vehiclewiring
harness.Check tosee if agood groundpath exists.
B. Thermostatand HeaterOperation
Turn off the ignition switch and cool the body
assemblyto below 40 degreesFahrenheit.
Note: If this test is performed in warm weather (above 30
deg. F) it may be necessary to remove the heater and
thermostat assembly and cool it in a freezer.
Using an ohmmeter, check the resistance between the
electrical pins in the connector. The resistance should be
1.5 to 1.7 ohms for the 12 volt heater assembly and 6.0 to
6.9 ohms for the 24 volt heater assembly. If the resistance
ishigher than themaximum stated, replacethe heaterand
thermostat assembly.
Warm the heater and thermostat assembly to over 90
degrees Fahrenheit and again check the resistance. The
resistance should exceed 1000 ohms. If the resistance
valuesobtained are withinthe stated limits,the thermostat
andheater assemblyis operatingproperly.If theresistance
values obtained are outside the stated limits, replace the
heater and thermostat assembly.

9
REPAIRING THE AD-SP™AIR DRYER GENERAL
If,after completingtheroutine operationand leakage tests,
ithas beendetermined thatoneor morecomponents ofthe
airdryer requiresreplacement or maintenance,refer tothe
following list to find the appropriate kit(s). When repairing
or replacing components of the air dryer use only genuine
Bendix parts.
MAINTENANCEKITSAVAILABLE:
109495 ...12 VOLTREPLACEMENTHEATERANDTHERMOSTAT
ASSEMBLYKIT
109496 ...24 VOLTREPLACEMENTHEATERANDTHERMOSTAT
ASSEMBLYKIT
109993 ...TURBO CUT-OFF MAINTENANCE KIT
5008414 .DESICCANTCARTRIDGEREPLACEMENT
109995 ...PURGE&RELIEFVALVEMAINTENANCEKIT
65677 ... The SC-PR™single check protectionvalve is
non-serviceable.Replace as anassembly.
WARNING! PLEASE READ AND FOLLOW
THESE INSTRUCTIONS TO AVOID
PERSONAL INJURYOR DEATH:
When working on or around a vehicle, the following
general precautions should be observed at all times.
1. Park the vehicle on a level surface, apply the
parking brakes, and always block the wheels.
Always wear safety glasses.
2. Stop the engine and remove ignition key when
working under or around the vehicle. When
working in the engine compartment, the engine
should be shut off and the ignition key should be
removed. Where circumstances require that the
enginebe in operation,EXTREMECAUTION should
be used to prevent personal injury resulting from
contact with moving, rotating, leaking, heated or
electrically charged components.
3. Do not attempt to install, remove, disassemble or
assemble a component until you have read and
thoroughly understand the recommended
procedures. Useonly the propertools and observe
all precautions pertaining to use of those tools.
4. If the work is being performed on the vehicle’s air
brake system, or any auxiliary pressurized air
systems,makecertainto drain the air pressurefrom
all reservoirs before beginning ANY work on the
vehicle. If the vehicle is equipped with an AD-IS™
air dryer system or a dryer reservoir module, be
sure to drain the purge reservoir.
5. Following the vehicle manufacturer’s
recommendedprocedures, deactivate the electrical
system in a manner that safely removes all
electrical power from the vehicle.
6. Never exceed manufacturer’s recommended
pressures.
7. Never connect or disconnect a hose or line
containing pressure; it may whip. Never remove a
component or plug unless you are certain all
system pressure has been depleted.
8. Use only genuine Bendix®replacement parts,
components and kits. Replacement hardware,
tubing, hose, fittings, etc. must be of equivalent
size, type and strength as original equipment and
be designed specifically for such applications and
systems.
9. Components with stripped threads or damaged
parts should be replaced rather than repaired. Do
not attempt repairs requiring machining or welding
unless specifically stated and approved by the
vehicle and component manufacturer.
10. Prior to returning the vehicle to service, make
certainallcomponentsandsystemsarerestoredto
their proper operating condition.
11. Forvehicleswith Antilock TractionControl(ATC),
the ATC function must be disabled (ATC indicator
lampshouldbeON)priortoperforminganyvehicle
maintenance where one or more wheels on a
drive axle are lifted off the ground and moving.
AD-SP™AIR DRYER REMOVAL
1. Parkthevehicleonalevelsurfaceandpreventmovement
by means other than the brakes.
2. Drain ALL reservoirs to 0 p.s.i. (0 kPa). - Caution:
Compressor discharge line may still contain
residual pressure.
3. Identify, mark and disconnect the supply, delivery and
control port air lines. Disconnect the wiring harness
connector from the heater and thermostat assembly
connector on the body assembly.
4. Ifsoequipped,disconnect,removeandsave theexhaust
line from the exhaust port of the air dryer.
5. Remove the three mounting bolts that secure the air
dryerto thevehicle andremove the airdryer.
Note: It is important to retain the three mounting bolts
since their length is specific to mounting the air dryer
without damage. If these bolts must be replaced, the
same length must be used.
6. RemovetheAD-SP™airdryerfromitsmountingbrackets
onthe vehicle.
DISASSEMBLY FOR PART REPLACEMENT
AND KIT INSTALLATION
1. Thefollowingdisassemblyandassemblyproceduresare
presentedforreference purposesand assumesthatthe
appropriate AD-SP™air dryer kits are on hand. The
instructions provided with these parts and kits should
befollowed insteadof the instructionspresented here.
2. The replacement parts and maintenance kits that are
available do not require full disassembly and in most
casesdonotrequire theremovaloftheAD-SP™airdryer
fromthevehicle.
3. If removal of the air dryer is necessary adhere to the
followingcaution:

10
Caution:WhileperformingserviceontheAD-SP™airdryer,it
is not recommended that a clamping device (vise,
C-clamp, etc.) be used to hold any die cast aluminum
componentasdamagemay result.Toholdthebody,installa
pipenippleinthesupplyportandclampthenippleintoa vise.
DISASSEMBLY - TURBO CUT-OFF VALVE
1. Loosenthe supplyport lineand allowany residualair in
the discharge line to drain.
2. Removetheretainingring fromthebody assembly, then
removetheturbocut-offcap fromthebody.Remove the
turbocut-off capo-ring.
3. Removethe turbocut-offpiston fromthe body.
4. Remove the large and small diameter o-rings from the
piston.
DISASSEMBLY - PURGE/RELIEF VALVE
1. Ifsoequipped,disconnect,removeandsave theexhaust
line from the exhaust port of the air dryer.
2. Removetheretainingring fromthebody assembly, then
removethe non-metallicexhaust coverand springfrom
the body. Note: The spring exerts a 30 pound force
againstthe exhaustcover.
3. Carefully remove the purge piston from the body and
removethe o-ringfrom thepurgepiston.
4. Thepurgevalve hastwodifferentsides. Notewhichside
is visible before removingthevalve. Removethevalve
fromthe body.
DISASSEMBLY - HEATER AND THERMOSTAT
1. Disconnect the vehicle wiring harness connector that
mateswith the heaterand thermostatconnector on the
body.Pry thelocktabsout,onthe vehiclewiringharness
connector,beforeremoval fromthe airdryer connector.
Makesureconnectorsealispresentonthevehiclewiring
harnessconnector.
2. Remove the retaining ring that secures the heater and
thermostat in the body.
3. Carefullypulltheheaterandthermostatassemblystraight
out of the body.
4. Removethe o-ringfromthe heaterconnector.
DISASSEMBLY - DESICCANT CARTRIDGE
1. Placeastrap wrenchor equivalenttoolon thedesiccant
cartridge next to the lip low on the cartridge and rotate
counterclockwise to removethe desiccant cartridge.
CLEANING, INSPECTION AND ASSEMBLY
PREPARATION
1. Cleanthe exterior ofthe body.
2. Using a clean rag, wipe the body bores clean.
3. Inspectforphysical damagetothebodycasting, broken
and or missing parts.
4. Inspect the interior and exterior of the body for severe
corrosion, pitting and cracks. Superficial corrosion and
or pitting on the exterior portion is acceptable.
5. Inspectthebores, valveseatingando-ringcontactareas
fordeepscuffingorgougesornicksthatwould notpermit
an air tight seal.
6. Inspect the pipe threads in the body. Make certain they
areclean andfree ofthreadsealant.
7. Inspect the purge valve piston seat for nicks and
excessivewear.
8. Inspect all air line fittings for corrosion. Clean all old
threadsealant fromthe pipe threads.
9. All o-rings removed should be discarded and replaced
withnew o-ringsprovided inappropriatekit(s).
10. Lubricatethe bodyboresando-ringgrooves, inthebody
and components, with a silicone grease only such as
those packaged with Bendix maintenance kits.
11. Lubricateallo-rings witha siliconegrease only,such as
those packaged with Bendix maintenance kits.
Any component exhibiting a condition described in step 3
to 8 should be replaced.
ASSEMBLY - TURBO CUT-OFF VALVE
1. Lubricateall o-ringswith asilicone greaseonly, suchas
those packaged with Bendix maintenance kits.
2. Installthelarge andsmalldiametero-ringson thepiston.
3. Install the turbo cut-off piston assembly in the body.
4. Installthe o-ring onthe turbocut-off cap theninstall the
cap in the body.
5. Installthe retainingringinthe body, makingcertainthat
it is fully seated in its groove.
6. Before placing vehicle back into service, perform the
Operation & Leakage Tests stated elsewhere in this
manual.
ASSEMBLY - PURGE/RELIEF VALVE
1. Lubricate the piston o-ring with a silicone grease only,
suchas thosepackaged with Bendixmaintenance kits.
Also lubricate completely around the outside edge of
thepurgevalve.
2. Installthe purge valvein thebody making certainthat it
isfirmlyand squarelyseatedinthebody withthecorrect
sidevisible.Note: Thethree"bumps"onthe purgevalve
should not be visible. If the 3 "bumps" are visible after
thepurge valve isinstalled, thevalve mustbe removed
andre-installed.

11
3. Install the o-ring on the purge piston, then install the
piston in the body taking care not to cut the piston
o-ring.
4. Install the non-metallic exhaust cover and spring in the
body.
5. Install the retaining ring in the ring in the body, making
certain that it is fully seated in its groove.
6. If so equipped, reconnect the exhaust line from the
exhaust port of the air
7. Before placing vehicle back into service, perform the
Operation & Leakage Tests stated elsewhere in this
manual.
ASSEMBLY - HEATER AND THERMOSTAT
1. Lubricate the connector o-ring with a silicone grease
only, suchas thosepackagedwithBendix maintenance
kits.
2. Installthe o-ringon theconnector,then slidethe heater
and thermostat assembly into the body making certain
notto cuttheo-ring. Notethat the"tab"on theassembly
fits into the corresponding slot in the body.
3. Install the retaining ring in the ring in the body, making
certain that it is fully seated in its groove.
4. Apply a dielectric grease on the heater and thermostat
connectorcontacts(both theheater andthermostatand
vehiclewiringharnessconnectorhalves).
5. After making certain the accordion seal is in place on
the vehicle wire harness connector, connect the wire
harness to the heater and thermostat assembly on the
dryer until its lock tab snaps ("clicks") into place.
6. Before placing vehicle back into service, perform the
Operation & Leakage Tests stated elsewhere in this
manual.
ASSEMBLY- DESICCANT CARTRIDGE
1. Lubricate the desiccant cartridge sealing ring with a
silicone grease only, such as those packaged with
Bendixmaintenance kits and replacementparts.
2. Screw the desiccant cartridge on to the body, by hand,
until the seal makes contact with the body and rotate
clockwise approximately one full turn. If necessary,
placea strapwrenchor equivalenttool onthedesiccant
cartridge next to the lip low on the cartridge.
3. Before placing vehicle back into service, perform the
Operation & Leakage Tests stated elsewhere in this
manual.
INSTALLATION
1. Install the assembled AD-SP™air dryer back onto the
vehicle using the same three mounting bolts retained
duringremoval.Tighten,thentorquethethreecapscrews
to 50 lb. ft.
2. Reconnect the three air lines to the proper ports on the
body(identified duringdisassembly). Ifthe fittingswere
removed from the body, use a thread sealant making
certainnone entersthe bodyduringre-installation
3. Apply a dielectric grease on the heater and thermostat
connectorcontacts(both theheater andthermostatand
vehiclewiringharnessconnectorhalves).
4. After making certain the accordion seal is in place on
the vehicle wire harness connector, connect the wire
harness to the heater and thermostat assembly on the
dryer by plugging it into the air dryer connector until its
lock tab snaps ("clicks") into place.
5. Ifsoequipped, reconnecttheexhaustline totheexhaust
portof the airdryer.
6. Before placing vehicle back into service, perform the
Operation & Leakage Tests stated elsewhere in this
manual.
RETROFITTING THE AD-SP™AIR DRYER
GENERAL
Thefollowingretrofitinstructionsare presentedforreference
purposes only since Bendix aftermarket retrofit and
replacement air dryers are packaged with the most up-to-
date installation instructions. The instructions packaged
with the AD-SP™air dryer should be followed instead of
thosepresented here.
Thepreceding portionofthis manualdeals with"in-service"
repairandorreplacementoftheAD-SP™airdryer.Theportion
of the manual that follows is concerned with installing an
AD-SP™airdryer ona vehiclenot previouslyequipped with
one.
VEHICLE APPLICATION REQUIREMENTS
The basic application requirements presented here apply
toa standard airdryer installation. Themajority ofvehicles
in use today will meet these basic requirements however,
some may not.
Thefollowing are examplesof vehicles where theAD-SP™
air dryer should not be used: bulk trailer unloading
operations,citytransit coaches,trashcompactorsand other
high air consumption or continuous flow systems. When
vehiclesof thistype areencountered otherBendix airdryer
modelsmustbeused.Consult yourlocalauthorized Bendix
partsoutletorsalesrepresentativeforadditional information.
1. Charge Cycle Time -TheAD-SP™air dryer is designed
to provide clean, dry air for the brake system. When a
vehicle's air system is used to operate non-brake air
accessories it is necessary to determine that during
normal,daily operation thecompressor shouldrecover
fromgovernor"cut-in" togovernor"cut-out" (usually100
psi to 120 psi) in 90 seconds or less at engine rpm's
commensurate with the vehicle vocation. Important
Note:TheAD-SP™air dryermustbeusedinconjunction

12
withgovernorswhich havea120 to130psi nominalcut-
outpressure. If agovernor isused that isnot withinthis
limitation contact your Bendix parts outlet or sales
representativefor additionalinformation. Ifthe recovery
time consistently exceeds this limit, it may be
necessary to "by-pass" the air accessory responsible
for the high air usage. Consult your local authorized
Bendixpartsoutlet orsales representativeforadditional
information.
2. PurgeCycleTime -Duringnormalvehicle operation,the
aircompressor mustremain unloadedfora minimumof
30 seconds. This minimum purge time is required to
ensurecompleteregeneration ofthedesiccant material.
If the purge time is occasionally shorter than the times
specified, no permanent ill effect should be expected,
however, if the purge time is consistently less than the
minimum, an accessory by-pass system must be
installed.
3. European Air Brake Systems - The AD-SP™air dryer
must not be installed in brake systems that
incorporatecompressorswithoutintegralunloading
mechanisms and/or utilize a compressor discharge
line unloader valve. When vehicles of this type are
encounteredotherBendixairdryermodelsmustbeused.
ConsultyourlocalauthorizedBendixpartsoutletorsales
representativeforadditional information.
4. Air Compressor Size - The AD-SP™air dryer was
designedprimarily forusewithcompressorsrated upto
30 CFM. It is recommended that when using the
AD-SP™air dryer with a compressor which has a rated
displacement exceeding 30 CFM that an authorized
Bendixparts outlet orBendix marketingrepresentative
be contacted for assistance.
5. Holset "E or QE" TypeAir Compressors - TheAD-SP™
airdryer canbe installedwiththe HolsetType"E orQE"
compressor. When theAD-SP™air dryer is used in this
installation,the HolsetECON valveshould beremoved
andthe specialorifice checkvalvein the"make-up" line
should be removed and replaced with a conventional
single check valve. This is most easily done using a
special 45 deg. supply port fitting, 112864, and single
checkvalve109710.
6. Use the following guidelines to determine the vehicle
applicationsuitablefor theAD-SP™air dryer:
Total Vehicle Res. AirDryer Model
Volume (Cu. In.)
Lessthan9,000 ...........................AD-SP™Air Dryer
Lessthan9,000w/several ........... AD-9™ExtendedPurge
airaccessoriesorhighair VolumeAirDryer
usage(e.g.transitcoaches
&refusehaulers)
Greaterthan9,000.......................AD-9™ExtendedPurge
VolumeAirDryeror
ContactBendixCommercial
VehicleSystemsLLC
VEHICLE PREPARATION
1. Parkthevehicleonalevelsurfaceandpreventmovement
by means other than the brakes.
2. Locate the front axle service (secondary) reservoir in
preparation for installing the SC-PR™single check
protectionvalve includedwithAD-SP™airdryerretro-fit
kits.
A. Withfull systempressure inall reservoirs,drain any
singlereservoirand observethereactionof thedash
gauges. If the supply reservoir was drained, no
reactionwill benoted on thedash gauges.Drain air
fromanother reservoir. When thefront axle service
reservoir gauge displays a pressure loss mark the
reservoirthatwasdrained.Confirmthatthe frontaxle
service (secondary) reservoir has been found by
building system pressure to governor cut-out and
drainingthe marked reservoir.After thereservoir is
completelydrainedmakeaservicebrakeapplication
andhaveanassistantobserve thefrontaxle service
brakes.Thefrontaxlebrakes shouldbeinoperative.
B. Some vehicles may be equipped with multi-
compartmentreservoirs.Thistypeofreservoiriseas-
ilyidentified bythe presenceof morethan onedrain
cock in the reservoir shell. The most common is a
two compartment reservoir with a "built-in" single
checkvalvebetweenthe twocompartments.Inmost
instances when this type of reservoir is in use, one
of the two compartments (usually the smallest) will
be the supply reservoir and the second compart-
mentwill beeitherthe frontor rearservice reservoir.
Drain air from either of the two compartments and
observethedashgauges.Ifthesupplyreservoircom-
partment was drained, no reaction will be noted on
the dash gauges. If one dash gauge displays pres-
surelossnotewhether itisthefrontaxle (secondary)
or rear axle (primary) reservoir. Mark the front axle
service(secondary)reservoir orcompartment.Con-
firmthat the correctreservoir has beenfound inthe
same manner described in 2A.
3. Locate the supply reservoir ("wet tank") and note if a
single check valve is installed in the discharge line
connectedtothereservoir.Ifasinglecheckvalveisfound
it should be removed before proceeding with the
installation.
4. Locate and mark the single check valve that is used to
protectand isolatethe frontaxle servicereservoir.
5. Drain all reservoirs to 0 p.s.i. (0 kPa).
LOCATING AD-SP™AIR DRYER ON VEHICLE
1. TheAD-SP™air dryermustbemounted vertically(purge
exhaust port toward road surface) outside the engine
compartmentin anarea ofairflow whilethe vehicleis in
motion. TheAD-SP™air dryer must not be exposed to
direct wheel splash (located behind axle mud flap is
acceptable).
2. LocatetheAD-SP™air dryerasclose tothefirst (supply)
reservoiras possible.

13
FIGURE 9 - AD-SP™SYSTEM PURGE AIR DRYER
MOUNTING BRACKET DIMENSIONS
3. Donot locatetheAD-SP™airdryernear heatproducing
components such as the vehicle exhaust and make
certain adequate clearance from moving components
(e.g. drive shaft, suspension, pitman arm, etc.) is
provided.
4. LocatetheAD-SP™airdryeronvehiclesothataminimum
of1” clearance abovethe cartridgeis availabletoallow
cartridge servicing. Additionally, provide access to the
bracket bolts so the unit may be removed when
necessary.
5. When choosing the mounting location for the AD-SP™
air dryer, note the discharge line length requirements
stated under the heading Connecting the Air Lines,
elsewherein this manual.
ImportantNote: Undernormaloperating conditions,the
maximuminlet airtemperature fortheAD-SP™air dryer
is150 degreesFahrenheit.
MOUNTING THE AD-SP™AIR DRYER
1. InstalltheAD-SP™air dryerbyreferring toFigure 2and
drillingthetriangularmountingholepatternin amounting
plate and then mounting the plate on the vehicle or by
drillingthemountingholepatternintheareaofthevehicle
chosen for mounting. Note: Check the vehicle manual
beforedrillingaframemember.
2. Important: Thelength ofthe threemountingboltsused
to attach theAD-SP™air dryer to the mounting plate is
very important. Refer to Figure 3. The threaded end of
the 1/2" - 13 UNC bolt must be between 1/8" below to
1/4"abovethe surfaceoftheAD-SP™airdryermounting
bracket surface when fully installed andtightened to
50 pound feet. Damage to the dryer body will result if
thebolt warning isignored.
Measure the thickness of all materials that the three
mountingbolts must passthrough. Small adjustments can
be made using flat washers under the bolt heads. Do not
use more than 3 flat washers.
3. Mount theAD-SP™air dryer on the vehicle using three
1/2"bolts(grade5min.)oftheproperlengthandwashers.
Torque to 50 lb. ft.
INSTALLING THE SC-PR™VALVE
1. Refer to steps 2A and 2B under Vehicle Preparation. If
thefront axle(secondary) reservoiris:
A. A single reservoir and not part of a multiple
compartment, proceed to step 2.
B. One compartment in a multiple compartment,
proceed to step 3.
2. Locatethe singlecheck valvethat protectsand isolates
the front axle reservoir and remove it. Remove the air
line fitting from the single check valve and install the
same fitting in the SC-PR™valve. Install the SC-PR™
valve and fitting in the reservoir port that was formerly
occupied by the single check valve. Reconnect the air
lineto theSC-PR™valve.Refer toFigure 12.
FIGURE 10 - AD-SP™SYSTEM PURGE AIR DRYER
MOUNTING BRACKET BOLT LENGTHS
2.835 INCHES
CENTER TO
CENTER
4.134 INCHES
CENTER TO CENTER
WIDTH (THICKNESS)
OF AD-SP™AIR DRYER
MOUNTING
BRACKET MOUNTING BOLT
1/8” BELOW
SURFACE
OF MTG.
BRACKET
VEHICLE FRAME
MEMBER
MOUNTING
BOLT
MOUNTING BOLT
1/4” ABOVE
SURFACE OF
MOUNTING
BRACKET
1/2” - 13 UNC
THREAD
(3 PLACES)

14
FIGURE 13 - SC-PR™SINGLE CHECK PROTECTION VALVE INSTALLED IN MULTI-COMPARTMENT RESERVOIR
FRONT AXLE COMPARTMENT
REAR AXLE RESERVOIR
SC-PR™
VALVE
SUPPLY COMPARTMENT
GOVERNOR
COMPRESSOR
FIGURE 11 - AIR SYSTEM WITHOUT AD-SP™SYSTEM PURGE AIR DRYER
FIGURE 12 - AIR SYSTEM WITH AD-SP™SYSTEM PURGE AIR DRYER
3. Locatean unused portin boththe supply compartment
andfrontaxle compartmentofthemultiple compartment
reservoir. Install the SC-PR™valve in the front axle
reservoir(orcompartment). Connect thesupply port of
theSC-PR™valve toeither anunused portinthe supply
compartmentofthereservoirORTeeintothelinebetween
the AD-SP™air dryer and the supply compartment of
the reservoir. Note: Use 3/8" air brake tubing. Refer to
Figure13.
CONNECTING THE AIR LINES
Important General Instructions
The instructions that follow apply to all installations of the
AD-SP™air dryer regardless of whether the AD-SP™air
dryer is replacing an existing air dryer or is being installed
ona vehicle that neverhad one installed.
If the vehicle is currently equipped with an air dryer some
additionalconsiderations apply.
A. IftheAD-SP™air dryeris replacingan integralpurge air
dryer, suchas theBendix®AD-9™air dryer,ona vehicle
equipped with any compressor except the Cummins-
Holset type E & QE, all that is necessary is that the air
dryerbe removed andthe existingairlines becorrectly
connected to theAD-SP™air dryer.
FRONT AXLE RESERVOIR
GOVERNOR
GOVERNOR
REAR AXLE SERVICE
COMPRESSOR
FRONT AXLE SERVICE
REAR AXLE RESERVOIR
SUPPLY RESERVOIR
COMPRESSOR
AD-SP™
AIR
DRYER
SUPPLY
FRONT AXLE SERVICE RESERVOIR
SINGLE CHECK VALVE
SC-PR™VALVE
INTERNAL SINGLE CHECK VALVE

15
B. IftheAD-SP™air dryeris replacingan integralpurge air
dryersuch as theBendix®AD-4™orAD-9™airdryer,on
a vehicle equipped with a Cummins-Holset type E or
QEcompressor,in addition toremoving theexisting air
dryer and correctly connecting the existing air lines to
theAD-SP™airdryer,itwill benecessary toremoveand
discardtheHolsetECONandspecialorificecheckvalve.
SeeFigure 8.
PURGE CONTROL LINE
1. Install a purge control air line having a minimum inside
diameter of 3/16 inches between theAD-SP™air dryer
controlportandanunusedunloaderportonthegovernor.
Thecontrol linemust beplumbed directto thegovernor
andnotin serieswith automaticdrainvalves, lubrication
systems, etc.
2. Thecontrol line shouldslope downward totheAD-SP™
airdryer withoutforming potential watertraps.
DISCHARGE LINE
General:
Refer toAppendixA, TableAfor recommended discharge
line lengths and sizes for various vehicle applications and
vocations.
PURGE EXHAUST LINE
1. If it is necessary to direct AD-SP™air dryer discharge
contaminatesaway fromvehiclecomponents a1” (25.4
mm)I.D. hosecan be clampedon theAD-SP™air dryer
exhaust
WIRING THE HEATER/THERMOSTAT
1. Determine the vehicle's electrical system voltage and
make certain that the AD-SP™air dryer that is to be
installedcontainsthesame voltageheater. Confirmthe
proper voltage by noting the color of the heater and
thermostatconnector.
Heater &Thermostat Connector
Voltage Color
12Volts ............................. White,(Noothermarkings)
24Volts ............................. Gray,orWhitew/RedDot
TheAD-SP™airdryer is availablewith eithera 12or 24 volt
heater and each uses 90 watts of power.
2. A separate wire harness and splice kit is with all
AD-SP™air dryer replacements and retro-fit kits. Refer
to the instructions contained in that kit for the proper
wiringprocedure.
TESTING THE AD-SP™AIR DRYER
GENERAL OPERATIONAL STATEMENT
The AD-SP™system purge air dryer, operates differently
than integral purge air dryers such as theAD-9™air dryer.
The "System Purge", designation is used because this air
dryer uses a small portion of the supply and front axle
(secondary) reservoir air pressure to purge or dry the
desiccant material. During the Purge cycle, an
approximately 8 - 14 psi drop in air pressure will be noted
onthe frontaxle (secondary)service reservoirdashgauge.
The drop in pressure is the result of using a small amount
of air from the reservoir to purge the AD-SP™air dryer
desiccant.
TheSC-PR™valveprotects theairpressure inthe frontaxle
(secondary)service reservoir,intheevent ofa compressor,
supply or rear axle reservoir failure or malfunction of the
AD-SP™airdryer purgecontrolvalving.
TESTING
Beforeplacing the vehiclein service, performthe following
tests:
1. Closeall reservoirdraincocks.
2. Build up system pressure to governor cut-out while
observing that both the front axle (secondary) and rear
axle service reservoir dash gauges rise equally in
pressure from 0 psi to governor cut-out. Note: When
building up brake system pressure to governor cutout
duringtesting, the engine/compressorshould berun at
approximately 1,800 rpm to simulate normal operation
ofthe vehicle.
Ifeither gaugefailsto displaythis condition,stoptesting
and check the installation of the SC-PR™valve. Note
thattheAD-SP™airdryerpurges withanaudible escape
ofair whengovernor cut-outpressure isreached.
3. Note that the front axle (secondary) service reservoir
pressure drops approximately 8 - 14 psi and that the
rearaxle servicereservoir losesno airpressure.
4. "Fan"the service brakesto reducesystem air pressure
togovernorcut-in.Notethatthesystemonceagainbuilds
to full pressure and is followed by a purge at the
AD-SP™air dryer exhaust.
5. Test theoperationof theSC-PR™valve.Buildsystem air
pressure to governor cut-out and turn the ignition off.
Drainthe supplyreservoir and notethat pressurein the
front axle (secondary) service reservoir does not drop
below 90 psi.
6. Itis recommendedthat thefollowing itemsbe testedfor
leakage to assure that the AD-SP™air dryer will not
cycle excessively:
(A) Totalair system leakage(See Bendix publication
BW-5057"Air Brake Handbook").
(B) Compressorunloader mechanism.
(C) Governor.
(D) Drain cock and safety valve in first (supply)
reservoir.
(E) All air connections leading to and from the first
(supply)reservoir.

16
AD-SP™AIR DRYER TROUBLESHOOTING CHART
SYMPTOMS
1. Dryer is constantly
“cycling”or purging.
Dryerpurges frequently
(every 4 minutes or less
whilevehicle is idling).
A. If leakage IS SHOWN on gauges test for
excessiveservice brake system leakage.
Allowableleakage:
Singlevehicle - 1 psi/minuteeither service
reservoir.
Tractortrailer - 3 psi/minuteeither service
reservoir. Repairandretestas required.
A. Excessive system
leakage.
IMPORTANT: Notewhether
air pressure loss is shown
ondash gauge(s). Pressure
loss shown on gauges is
causedby service brake
system or component
leakage.Pressureloss NOT
SHOWN on gauges is
caused by supply system or
componentleakage.
CAUSE REMEDY
B. If leakage is NOT SHOWN on gauges test for
excessive supply system leakage.
Removedrain cockor valvein supplyreservoir (wet
tank) and install air gauge. Build system pressure,
allowair dryer topurge and observeair gauge in
supplyreservoir.Pressure drop shouldnotexceed 1
psi per minute. Perform tests 1 to 5 in the order
presented.

17
1. Test fittings, hoses, lines and connections.Apply
soap solution to detect excessive leakage.
Tightenor replace as neededthen repeat theair
dryercharge-purge cycleand observethegauge
installed in the supply reservoir. If leakage is
withinlimits removegauge fromreservoir and
replacedrain cock orvalve. Ifexcessiveleakage
is detected, continue testing.
2. Test accessoriesconnected to supply reservoir.
Drain all air pressure from system, disconnect all
air lines leading to accessories (fan clutch,
wipers, air seats, etc.) and plug the reservoir at
disconnection point. Build air system pressure
untilair dryer purgesandobserve supply
reservoirgauge. If leakageis nolonger
excessive,repairor replaceleaking accessory. If
excessive leakage is detected, continue testing.
3. Test governorleakage. Build systempressureto
governorcut-out, turnoffengine andapply soap
solutionto governor exhaustport andaround
cap. Leakage should not exceed a 1" bubble in 5
seconds. Reduce system pressure to 80 psi or
less, and re-apply soap solution. Leakage should
not exceed a 1" bubble in 5 seconds. If
excessive leakage is detected in either test,
repairorreplace governor.
4. Testcompressor unloader leakage.Drain all air
pressurefrom systemand removethe governor
fromthe compressor.Temporarily plugthe
governorunloader port orair line thatmated with,
or connected to, the compressor. Build air
system pressure until air dryer purges then
IMMEDIATELYSHUTOFFTHEENGINE.
Observethe air gaugein thesupply reservoir. If
leakage is within limits, replace the compressor
unloaders.Re-connect thegovernorto the
compressor(after removing pluginstalled in
governor)and retestwhile observingsupply
reservoirgauge. If excessiveleakage isdetected,
continuetesting.
5. Testair dryerpurgevalveandoutlet (delivery)
checkvalve.Drain all air pressurefrom system,
remove the control line connection at the air
dryer and plug the end of the air line leading to
thegovernor (not the airdryer control port).Build
systempressure to governorcut-out andobserve
airgauge. If little orno pressure dropis observed
replacethe air dryercheck valve. Ifpressure drop
continues, apply soap solution to air dryer purge
exhaustand purge control port(where the control
linewas removed). Leakageshould not exceed a
1" bubble in 5 seconds. If leakage is excessive
repairorreplace purgevalve assembly.
AD-SP™AIR DRYER TROUBLESHOOTING CHART (Continued)
SYMPTOMS CAUSE REMEDY

18
AD-SP™AIR DRYER TROUBLESHOOTING CHART (Continued)
SYMPTOMS CAUSE REMEDY
B. Locatethe SC-PR™valve onthe front axle
service(secondary) reservoirand replace.
C. Minimumsetting required forAD-SP™air dryer
installation 100 cut in and 120 cut out. Test
operationof governor.Repairorreplace as
necessary.
D. Withgauge installed at RESport of governor,
pressureshould not dropbelow"Cut In"
pressure at the onset of the compressor
"Unloaded" cycle. If pressure drops, check for
"kinks" or restrictions in line connected to RES
port.Line connected to RESport on governor
mustbe same diameter, or preferablylarger
than, lines connected to UNL port(s) on
governor.
E. Eliminate all leakage possibilities in 1A -
ReplaceAD-SP™airdryer.
F. Refer to the "VehicleApplication
Requirements" section of this manual and
verifyapplication.
B. Leaking(internal or
external)SC-PR™single
checkprotection valve.
C. Incorrectgovernorsetting
ormalfunctioning
governor.
D. Rapid cycling of the
governordue toair
starvationatthe RES
portofthegovernor.
E. Leakingpurge control
mechanismor delivery
checkvalve inAD-SP™
airdryer.
F. High airusage - Vehicle
application.
2. Water and/or Oil in
Supplyor Service
Reservoir.
A. Improperdischarge line
lengthor improperline
material.Maximum air
dryerinlettemperature is
exceeded.
B. Air system charged from
outsideair source
(outsideairnot passing
throughair dryer).
C. Airdryer not purging
(see Symptom #5).
A. Refer to section entitled Connecting the Air Lines
as well asAppendix A, TableAcolumns 1 & 2
then and check line size and length.
B. If system must have outside air fill provision,
outside air should pass through air dryer. This
practice should be minimized.
C. See Symptom #5.
D. Purge(air exhaust) time
insufficientdue to
excessive system
leakage(see causes for
Symptom #1).
D. Check causes and remedies for Symptom #1.
E. Excessive air usage,
duty cycle too high - Air
dryernot compatible
with vehicle air system
requirement(Improperair
dryer/vehicle
application).
E. SeeAppendixA, TableA, column 1, for
recommendedcompressor sizes. If the
compressoris “too small” forthe vehicle vocation
(forexample, where avehicle’s vocationhas
changedor service conditions exceedthe
originalvehicle or engine OEspec’s) then
upgradethecompressor. Note:The costs
incurred (e.g. installing a larger capacity
compressor, etc.)are notcoveredunder original
compressorwarranty.

19
AD-SP™AIR DRYER TROUBLESHOOTING CHART (Continued)
SYMPTOMS CAUSE REMEDY
NOTE: Duty Cycle is the
ratio of time the compressor
spends building air to total
enginerunning time.Air
compressorsare designed
tobuild air (run“loaded”) up
to 25% of the time. Higher
duty cycles cause
conditions that affect air
brakecharging system
performancewhich may
requireadditional
maintenance. Factors that
add to the duty cycle are: air
suspension,additional air
accessories, use of an
undersizedcompressor,
frequentstops, excessive
leakagefrom fittings,
connections, lines,
chambersor valves,etc.
Charge Cycle Time - TheAD-SP™air dryer is
designedto provide clean, dryair for thebrake
system. When a vehicle’s air system is used to
operate non-brake air accessories it is
necessary to determine that; during normal,
dailyoperation the compressorshould recover
fromgovernor “cut-in”togovernor “cut-out”
(usually 100 psi to 120 psi) in 90 seconds or
less at engine RPM’s commensurate with the
vehiclevocation. If therecovery time consistently
exceeds this limit, it may be necessary to
“bypass” the air accessory responsible for the
high air usage.An example of where a by-pass
system would be required is when the
compressor is used to pressurize a tank trailer
forpurposes ofoff-loading product. Consultyour
local authorized Bendix parts outlet or sales
representativefor additionalinformation.
PurgeCycle Time- During normalvehicle
operation, the air compressor must remain
unloaded for a minimum of 30 seconds. This
minimum purge time is required to ensure
completeregeneration of the desiccantmaterial.
If the purge time is consistently less than the
minimum, an accessory by-pass system must
be installed. Consult your local authorized
Bendixparts outlet or salesrepresentative for
additionalinformation.
Air Compressor Size -Although theAD-SP™air
dryer can be used in conjunction with larger
compressors, it was designed primarily for units
rated for up to 30 CFM. It is recommended that
when using theAD-SP™air dryer with a
compressor which has a rated displacement
exceeding 30 CFM that an authorized Bendix
partsoutlet or Bendixmarketing representative
be contacted for assistance.
F. Restricted discharge line. SeeAppendixA, Table
A, column 1 & 2 for recommended sizes. If
discharge line is restricted or more than 1/16"
carbonbuildup is found,replace the discharge
line. Replace as necessary.
DischargeLine Freeze-Up: Thedischarge line must
maintain a constant slope down from the
compressor to the air dryer inlet fitting to avoid low
points where ice may form and block the flow. If,
instead, ice blockages occur at the air dryer inlet,
insulation may be added here, or if the inlet fitting is
a typical 90 degree fitting, it may be changed to a
straightor 45 degree fitting.For more informationon
howto help preventdischarge line freeze-ups,see
BendixBulletins TCH-08-21andTCH-08-22.Shorter
dischargelinelengths or insulationmay be required
in cold climates.
F. Air compressor
dischargeand/or air
dryerinlet temperature
too high.

20
AD-SP™AIR DRYER TROUBLESHOOTING CHART (Continued)
SYMPTOMS CAUSE REMEDY
Insufficientcoolant flow throughcompressor.Inspect
coolant line. Replace as necessary (I.D. is 1/2"
min.). Inspect the coolant lines for kinks and
restrictions and fittings for restrictions. Replace as
necessary. Verify coolant lines go from engine block
to compressor and back to the water pump. Repair
as necessary.
Restricted air inlet (not enough air to compressor).
Check compressor air inlet line for restrictions,
brittleness, soft or sagging hose conditions etc.
Repair as necessary. Inlet line size is 3/4 ID.
Maximumrestrictionrequirement for compressorsis
25 inches of water. Check the engine air filter and
service if necessary (if possible, check the air filter
usageindicator).
Poorly filtered inlet air (poor air quality to
compressor).Check for leaking,damaged or
malfunctioningcompressor air inletcomponents
(e.g. induction line, fittings, gaskets, filter bodies,
etc.). Repair inlet components as needed. Note: Dirt
ingestion will damage compressor and is not
coveredunderwarranty.
Ifyoufound excessive oilpresent in the service
reservoirand you did notfind any issuesabove, the
compressor may be passing oil.
Replacecompressor.If still underwarranty, follow
normalwarranty process.
G. If you foundexcessive oil presentin the service
reservoirand you did notfind any issuesabove,
the compressor may be passing oil. Test the
compressor using the BASIC cup method as
describedinthe Bendix compressorservice
manual and referred to inAppendixA,TableA,
column 5.
Replacecompressor.If still underwarranty, follow
normalwarranty process.
H. When replacing the desiccant cartridge, make
sure desiccant cartridge assembly is properly
installed and sealing rings are in place on
mountingsurface of desiccant cartridge.
I. Replace desiccant cartridge assembly. Refer to
AppendixA, TableAcolumns 3 & 4 for
recommendedintervals.
G. Compressor malfunction.
H. Air by-passes desiccant
cartridgeassembly.
I. Desiccantrequires
replacement.