BENDIX AD-9 AIR DRYER User manual

1
CONTROL
PORT
SUPPLY
PORT
SD-08-2412
Bendix®AD-9™Air Dryer
EXTENDED PURGE AD-9™AIR DRYER STANDARD AD-9™AIR DRYER
OUTER
SHELL
WIRING HARNESS
CONNECTION
DELIVERY PORT
DESCRIPTION
ThefunctionoftheAD-9™airdryeristocollectandremove
airsystemcontaminantsinsolid,liquidandvaporformbefore
theyenterthebrakesystem.It provides clean, dry airtothe
componentsofthebrakesystem which increases thelifeof
the system and reduces maintenance costs. Daily manual
drainingofthereservoirsiseliminated.
TheAD-9™airdryerconsistsofadesiccantcartridgeanda
die cast aluminum end cover secured to a cylindrical steel
outer shell with eight cap screws and nuts. The end cover
contains a check valve assembly, a safety valve, three
threaded air connections and the purge valve housing
assembly. The removable purge valve housing assembly
incorporatesapurgevalve mechanism andaturbocharger
cut-off feature that is designed to prevent loss of engine
“turbo”boostpressure during the purge cycle of theAD-9™
airdryer.Forease of serviceability,the desiccant cartridge
anddischargecheck valve assemblyarescrewin type.The
purge valve housing assembly, which includes the heater
and thermostat assembly, and the discharge check valve
assembly, is serviceable from the exterior of the air dryer,
while servicing the screw-in desiccant cartridge requires
removaloftheairdryerassemblyfromthevehicle.
The AD-9™air dryer has three female pipe thread air
connections and each is identified as follows:
Port l.D. Function/Connection
CON 4............... ControlPort
(purgevalvecontrol andturbocut-off).
SUP 11 ............. Supply Port (air in).
DEL 2 ............... DeliveryPort(airout).
OUTER
SHELL
SUPPLY
PORT
WIRING HARNESS
CONNECTION
DELIVERY PORT
CHECK
VALVE
ASSEMBLY
END COVER
CHECK
VALVE
ASSEMBLY
END COVER
CONTROL
PORT
FIGURE 1 - AD-9™AIR DRYER MODELS

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ORIFICE
PURGE
VOLUME
DELIVERY
PORT
HEATER
ELEMENT
SUMP
EXHAUST
PURGE
VALVE
RESERVOIR
SUPPLY
PORT
COMPRESSORGOVERNOR
ENGINE
TURBO
CONTROL
PORT
OIL
SEPARATOR
DESICCANT
BED
DESICCANT
CARTRIDGE
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CHECK
VALVE
OPERATION OF THEAD-9™AIR DRYER
The AD-9™air dryer alternates between two operational
modes or “cycles” during operation: the charge cycle and
the purge cycle. The following description of operation is
separatedintothese“cycles”ofoperation.
CHARGE CYCLE (refer to Figure 2)
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
supplyportoftheairdryerendcover.As air travels through
theendcoverassembly,itsdirectionof flowchangesseveral
times, reducing the temperature, causing contaminants to
condense and drop to the bottom or sump of the air dryer
endcover.
After exiting the end cover, the air flows into the desiccant
cartridge. Once in the desiccant cartridge air first flows
throughanoilseparatorwhich removes water inliquidform
as well as oil and solid contaminants.
Air exits the oil separator and enters the desiccant drying
bed.Air flowing through the column of desiccant becomes
FIGURE 2 - AD-9™AIR DRYER CHARGE CYCLE
progressivelydrieraswater vapor adheres to thedesiccant
materialinaprocessknown as “adsorption”. The desiccant
cartridge using the adsorption process typically removes
95%ofthewatervaporfromthepressurized air.
Themajorityofdryairexitsthedesiccantcartridgethrough
itsintegralsinglecheckvalvetofillthepurgevolumebetween
the desiccant cartridge and outer shell. Some air will also
exitthedesiccantcartridgethroughthepurgeorificeadjacent
tothecheckvalve.
Dry air flows out of the purge volume through the single
check valve assembly and out the delivery port to the first
(supply)reservoiroftheairsystem.
The air dryer will remain in the charge cycle until air brake
system pressure builds to the governor cutout setting.
PURGE CYCLE (refer to Figure 3)
Whenairbrakesystempressure reaches thecutoutsetting
of the governor, the compressor unloads (air compression
stopped)andthepurgecycleoftheairdryerbegins.When
the governor unloads the compressor, it pressurizes the
compressor unloader mechanism and line connecting the
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CHECK
VALVE
ASSEMBLY
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vaporadheringtoit.Generally15-30secondsarerequired
fortheentirepurgevolumeofastandardAD-9™air dryer to
flowthroughthedesiccantdryingbed.
The end cover single check valve assembly prevents air
pressureinthebrakesystemfromreturningtotheairdryer
during the purge cycle.After the 30 second purge cycle is
complete,theairdryerisreadyforthenext charge cycle to
begin.
The purge valve will remain open after the purge cycle is
completeandwillnotclose until air brake system pressure
is reduced and the governor signals the compressor to
charge.
TURBO CUT-OFF FEATURE (Refer to Figure 4)
Theprimary function of the turbocut-off valve is to prevent
lossofengineturbochargerair pressure through theAD-9™
air dryer in systems where the compressor intake is
connectedtotheengineturbocharger.Theturbocut-offvalve
alsoreducesthe“puffing”ofairouttheopenexhaustwhen
anaturallyaspirated,singlecylindercompressorequipped
with an inlet check valve is in use.
CHECK
VALVE ORIFICE
PURGE
VOLUME
DELIVERY
PORT
HEATER
ELEMENT
SUMP
EXHAUST
PURGE
VALVE
RESERVOIR
SUPPLY
PORT
COMPRESSORGOVERNOR
ENGINE
TURBO
CONTROL
PORT
OIL
SEPARATOR
DESICCANT
BED
DESICCANT
CARTRIDGE
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TURBO
CUTOFF
PISTON
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CHECK
VALVE
ASSEMBLY
FIGURE 3 - AD-9™AIR DRYER PURGE CYCLE
governorunloaderporttotheAD-9™airdryerendcovercontrol
port. The purge piston moves in response to air pressure
causingthepurgevalvetoopentoatmosphereand(partially)
closingoffthe supplyofairfromthecompressor,thiswill be
further discussed in the section covering the turbo cut-off
feature. Contaminants in the end cover sump are expelled
immediately when the purge valve opens. Also, air which
wasflowingthroughthedesiccantcartridgechangesdirection
andbeginstoflowtowardtheopenpurgevalve.Oil andsolid
contaminantscollectedbythe oil separator areremovedby
airflowingfromthedesiccantdryingbedtotheopenpurge
valve.
Theinitialpurgeanddesiccantcartridgedecompressionlasts
onlyafewsecondsandisevidencedbyanaudibleburstof
air at theAD-9™air dryer exhaust.
The actual reactivation of the desiccant drying bed begins
asdryairflowsfromthepurgevolumethroughthedesiccant
cartridge purge orifice and into the desiccant drying bed.
Pressurizedairfromthepurgevolumeexpandsafterpassing
through the purge orifice; its pressure is lowered and its
volumeincreased.The flowofdryair throughthedryingbed
reactivates the desiccant material by removing the water
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FIGURE 4 - AD-9™AIR DRYER TURBO CUTOFF
At the onset of the purge cycle, the downward travel of the
purgepiston isstoppedwhentheturbocut-offvalve(tapered
portion of purge piston) contacts its mating metal seat in
thepurgevalvehousing. Withtheturbocut-offvalve seated
(closed position), air in the discharge line and AD-9™air
dryerinletport is restrictedfromenteringthe airdryer. While
the turbo cut-off effectively prevents loss of turbo charger
boostpressureto theengine,some“seepage”of airmaybe
detectedundercertainconditionsofcompressorengineand
turbo charger operation, even so there will always be low
pressuretrappedinthedischargeline.
PREVENTIVE MAINTENANCE
Important: Review the warranty policy before performing
anyintrusivemaintenanceprocedures.Anextendedwarranty
maybevoidedif intrusive maintenance isperformedduring
thisperiod. Note: Itisacceptablefor the purge valve to be
maintained as necessary, i.e., the installation of a purge
valvemaintenancekit,without voiding thewarranty.
Becausenotwovehiclesoperateunder identicalconditions,
maintenanceandmaintenanceintervalswillvary.Experience
is a valuable guide in determining the best maintenance
intervalforanyone particular operation.
Every900 operatinghoursor 25,000miles orevery three
(3)months:
1. Check for moisture in the air brake system by opening
reservoirs, drain cocks, or valves and checking for
presenceofwater.Ifmoistureis present, the desiccant
may require replacement; however, the following
conditions can also cause water accumulation and
shouldbeconsideredbeforereplacingthedesiccant:
UPPER
BRACKET
CHECK
VALVE
ASSEMBLY
SUPPLY
PORT
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UPPER
BRACKET
STRAP
DESICCANT
CARTRIDGE
LOWER
BRACKET
HOUSING
CHECK
VALVE
ASSEMBLY
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DISCHARGE
LINE
TURBO
CUTOFF
PISTON EXHAUST
PURGE
VALVE
TURBO
CUTOFF
PISTON
A. An outside air source has been used to charge the
system. This air did not pass through the drying bed.
B. Airusage is exceptionally high and not normal for a
highway vehicle. This may be due to accessory air
demandsorsomeunusualairrequirement thatdoes
not allow the compressor to load and unload
(compressing and non-compressing cycle) in a
normal fashion. Check for high air system leakage.
If the vehicle vocation has changed it may be
necessarytoupgradethe compressorsize.Referto
AppendixA,TableAandthecolumnentitledVehicle
Vocation.
C. The air dryer has been installed in a system that
has been previously used without an air dryer.This
type of system will be saturated with moisture and
severalweeksofoperationmay be required to dryit
out.
D. Location of the air dryer is too close to the air
compressor. Refer to Locating AD-9™Air Dryer On
Vehicle section andAppendixA, TableA, column 2
fordischargelinelength.
E. In areas where more than a 30 degree range of
temperature occurs in one day, small amounts of
water can accumulate in the air brake system due
to condensation. Under these conditions, the
presence of small amounts of moisture is normal
PURGE VALVE
HOUSING
ASSEMBLY PURGE
VALVE DISCHARGE
PORT
FIGURE 5 - AD-9™AIR DRYER SECTIONAL VIEW
DESICCANT
BED
OIL
SEPARATOR
CONTROL
PORT
SUPPLY
PORT

5
and should not be considered as an indication that
thedryerisnotperformingproperly.
Note:Asmallamountof oilinthesystem maybenormal
and should not, in itself, be considered a reason to
replacethedesiccant; oil staineddesiccantcanfunction
adequately.
2. Check mounting bolts for tightness. Retorque to 270-
385inchpounds.
3. Perform the Operation & Leakage Tests listed in this
publication.
Every 10,800 hours; 300,000 miles or 36 months:
1. Rebuildthe airdryerincludingthedesiccantcartridge.
Note: Thedesiccantchangeintervalmay vary from vehicle
to vehicle.Although typical desiccant cartridge life is three
years, many will perform adequately for a longer period of
time.Inordertotakemaximumadvantageofdesiccantlife
andassurethatreplacementoccursonlywhennecessary,
itisimportantthatOperation&Leakage Testsbe performed.
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
1. Test the outlet port check valve assembly by building
the air system to governor cut-out and observing a test
air gauge installed in the #1 reservoir. A rapid loss of
pressurecouldindicateafailedoutletportcheckvalve.
This can be confirmed by bleeding the system down,
removingthecheckvalve assemblyfromtheendcover,
subjectairpressure totheunitand applyasoapsolution
tothecheck valveside.Leakageshouldnot exceeda1”
bubble in 1 second.
2. Check for excessive leakage around the purge valve.
Withthecompressorin loadedmode(compressingair),
apply a soap solution to the purge valve housing
assembly exhaust port and observe that leakage does
not exceed a 1” bubble in 1 second. If the leakage
exceedsthe maximumspecified,servicethepurge valve
housingassembly.
3. Closeallreservoirdraincocks. Buildupsystempressure
togovernorcut-out andnotethatAD-9™airdryerpurges
with an audible escape of air. “Fan” the service brakes
to reduce system air pressure to governor cut-in. Note
thatthesystemonceagain builds to full pressureandis
followedbyanAD-9™air dryer purge.
LOWER
MOUNTING
BRACKET
AD-9™
AIR DRYER
AD-9™
END COVER FEMALE
CONNECTOR
MALE
CONNECTOR
LATCH MUST BE
INSERTED UNTIL
IT SNAPS OVER
TAB ON MATING
CONNECTOR
SIDE VIEW END VIEW
A two lead, 12 inch, wire harness with attached weather
resistant connector is supplied with all retrofit and
replacement AD-9™air dryers. Connect one of the two
leads of the wire harness to the engine kill or ignition
switch. The remaining lead of the wire harness must be
connected to a good vehicle ground. A fuse should be
installed in the power carrying wire; install a 10 amp fuse
for 12 volt heaters and a 5 amp fuse for a 24 volt heater.
Use 14 AWG wire if it is necessary to lengthen the wire
harness provided.
Make certain all wire splices are waterproofed.
Tie wrap or support all electrical wire leading to the
AD-9™air dryer.
FIGURE 6 - HEATER AND THERMOSTAT CONNECTOR
4. Check the operation of the safety valve by pulling the
exposed stem while the compressor is loaded
(compressingair).There mustbeanexhaustofairwhile
the stem is held and the valve should re-seat when the
stem is released.
5. Check all lines and fittings leading to and from the air
dryerforleakageandintegrity.
6. Check the operation of the end cover heater and
thermostat assembly during cold weather operation as
follows:
A. Electric Power to the Dryer
With the ignition or engine kill switch in the ON
position, check for voltage to the heater and
thermostatassemblyusingavoltmeterortestlight.
Unplug the electrical connector at the air 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,brokenwires,orcorrosion in thevehiclewiring
harness.Checktoseeifagoodgroundpathexists.

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B. ThermostatandHeaterOperation
Turn off the ignition switch and cool the end cover
assemblytobelow 40degreesFahrenheit.Using an
ohmmeter, check the resistance between the
electricalpinsinthefemaleconnector.Theresistance
should be 1.5 to 3.0 ohms for the 12 volt heater
assemblyand6.8to9.0ohmsforthe24voltheater
assembly. Note: Some early models of the AD-9™
air dryer will have resistance readings of 1.0 to 2.5
ohmsforthe12voltheaterassemblyand4.8to7.2
ohms for the 24 volt heater assembly. If the
resistance is higher than the maximum stated,
replace the purge valve housing assembly, which
includes the heater and thermostat assembly.
Warm the end cover assembly to over 90 degrees
Fahrenheit and again check the resistance. The
resistance should exceed 1000 ohms. If the
resistance values obtained are within the stated
limits, the thermostat and heater assembly is
operatingproperly.Iftheresistance valuesobtained
areoutsidethe stated limits,replacethepurge valve
housing assembly, which includes the heater and
thermostat assembly.
REBUILDING THE AD-9™AIR DRYER
GENERAL
If,aftercompletingtheroutineoperation and leakage tests,
ithasbeendetermined that one ormorecomponentsofthe
airdryerrequiresreplacementormaintenance,refertothe
followinglisttofindthe appropriate kit(s).
When rebuilding or replacing components of the air dryer
use only genuine Bendix parts. For ease in servicing the
AD-9™air dryer desiccant cartridge assembly, it is
recommendedthattheairdryerberemovedfromthevehicle.
MAINTENANCE KITS AVAILABLE:
5005037 HardSeatPurgeValveHousingMaintenanceKit
5005893 Soft SeatPurgeValve Housing MaintenanceKit
Thesekitscontainthepartsnecessarytorebuild
the air portion of the purge valve housing and do
notincludetheheaterand thermostat.
107796 Remanufactured Desiccant Cartridge
ReplacementKit
This kit contains the parts necessary to change
the desiccant cartridge only.
107794 DesiccantCartridgeReplacementKit
This kit contains the parts necessary to change
the desiccant cartridge only.
107799 EndCoverCheckValveAssemblyReplacement
3/4 inch thread size.
107800 EndCoverCheckValveAssemblyReplacement
1/2 inch thread size.
800405 ServiceNew PurgeValveHousingAssembly-
SoftSeat (w/heaterandthermo.)12volt
system.
5004341 RemanufacturedExchangePurgeValve
HousingAssembly - Soft Seat (w/heater and
thermo.) 12 volt system.
5004479 ServiceNewPurgeValveHousingAssembly-
HardSeat
(w/heaterandthermo.)12voltsystem.
5004339 ServiceNewPurgeValveHousingAssembly-
DLU(w/heaterandthermo.)12voltsystem.
5004338 ServiceNewPurgeValveHousingAssembly-Soft
Seat(w/heaterandthermo.)24 volt system.
5004342 RemanufacturedExchange PurgeValveHousing
Assembly - Soft Seat (w/heater and thermo.) 24
volt system.
5004480 ServiceNew ValveHousingAssembly-HardSeat
(w/heaterandthermo.)24voltsystem.
5004340 ServiceNewPurgeValveHousingAssembly-DLU
(w/heaterand thermo.) 24 volt system.
107695 CompleteMounting Bracket Kit
Thiskitcontainstheupperand lower brackets as
well as the necessary hardware items to mount
them.
GENERAL SAFETY GUIDELINES
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
engine bein operation, EXTREMECAUTIONshould
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. Useonlythe proper tools andobserve
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,make certaintodrain theair 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.

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FIGURE 7 - AD-9™AIR DRYER ASSEMBLY
7
4
3
9
13
14
10
11
2
18
5
15
17
20
17
1
6
16
12
23
21
22
END
COVER
25
26
24
19
17
8
28
27
ITEM DESCRIPTION
1 O-RING
2 PURGE VALVE GUIDE
3 1/4" TAPPING SCREW
4 SHOULDER BOLT
5 O-RING
6 O-RING - (NOT USED ON DLU MODELS)
7 O-RING
8 PURGE VALVE ASSEMBLY (COMPLETE)
9 PURGE VALVE HOUSING
10 HARD SEAT PURGE PISTON
11 PURGE VALVE
12 SAFETY VALVE
13 SPRING
14 QUAD-RING
15 DELIVERY CHECK VALVE ASSEMBLY
16 3/8" CAP SCREW
17 3/8" WASHER
18 3/8" CAP SCREW (LONG)
19 LOCKNUT
20 LOWER MOUNTING BRACKET
21 O-RING
22 DESICCANT CARTRIDGE ASSEMBLY (COMPLETE)
23 O-RING
24 OUTER HOUSING
25 5/16" X 4-1/2" UPPER BRACKET CAP SCREW
26 UPPER MOUNTING BRACKET STRAP
27 UPPER MOUNTING BRACKET SADDLE
28 SLEEVE NUT

8
5. Following the vehicle manufacturer’s
recommendedprocedures,deactivate theelectrical
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
certain all components and systems are restored
to their proper operating condition.
11. For vehicles with Antilock Traction Control (ATC),
the ATC function must be disabled (ATC indicator
lampshouldbe ON) prior toperformingany vehicle
maintenance where one or more wheels on a drive
axle are lifted off the ground and moving.
AD-9™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 and disconnect the three air lines from the end
coverandnote the positionofendcover portsrelativeto
thevehicle.
4. Unplug the vehicle wiring harness from the heater and
thermostat assembly connector on the purge valve
housingassembly.
5. Loosen the 5/16" X 4-1/2" hex cap screw (25) securing
theuppermountingstrap(26).
6. Remove, retain and mark the two 3/8" end cover cap
screws (18), lock nuts (19) and four special washers
(17) that retain the lower mounting bracket (20) to the
end cover, also mark these two holes of the end cover.
(Theseboltsare longer than the other 6 bolts.)
7. RemovetheAD-9™air dryer from itsmountingbrackets
onthevehicle.
DISASSEMBLY
The following disassembly and assembly procedure is
presented for reference purposes and presupposes that a
major rebuild of the AD-9™air dryer is being undertaken.
Severalreplacementpartsandmaintenancekitsareavailable
which do not require full disassembly. The instructions
providedwiththesepartsand kits shouldbefollowedinlieu
oftheinstructionspresentedhere.RefertoFigure7during
disassembly.
Caution: While performing service on the AD-9™air
dryer, it is not recommended that a clamping device
(vise, C-clamp, etc.) be used to hold any die cast
aluminum component as damage may result. To hold
the end cover, install a pipe nipple in the supply port
and clamp the nipple into a vise.
1. Usingan adjustablewrenchoran 1-3/4"socket,remove
the delivery check valve assembly (15) and o-ring (1).
Removetheo-ring(1)from the check valve assembly.
2. Removethethree1/4"selftappingscrews(3)thatsecure
the purge valve housing assembly to the end cover
assembly. Pullthepurgevalvehousing assembly (8)out
oftheendcoverassembly.Removetheo-rings(5,6 &7)
from the exterior of the purge valve housing assembly.
(O-ring item 6 is not included in DLU models.) Note: the
o-rings may be lodged in the end cover bores, if so, they
mustberemoved.
3. PurgeValve(8)Disassembly:
Note: Removalof thepistonfromthepurgevalvehousing
assembly requires a tool to hold the head of the purge
piston while unscrewing the purge valve shoulder bolt
(4). If an extended type exhaust cover is in use to
accommodate the attachment of an exhaust hose, the
exhaustcovermustbecarefullypeeledoffofthepurge
valve housing (9). Use a thin flat blade to pry the
exhaust cover off, taking care not to damage the
potting material (RTV sealant) under the cover. To
remove the piston (10) from the purge valve housing
assembly (9)(9) use a twelve point 1/4" socket to hold
theheadoftheshoulderbolt(4).
A. Removetheshoulderbolt(4)fromthe bottom of the
purgevalvehousingassembly(8)while securingthe
top of the purge piston (10) using the two opposing
castindentationsandatool. Removethepurgeguide
(2)andpurgevalve(11)fromthepurgevalvehousing.
B. Removethepurgepiston(10) and return spring (13)
from the opposite end of the purge valve housing.
Removethequadring(14)fromthepurgepiston(10).
C. Heater and Thermostat Assembly Replacement.
Caution: Do not attempt to remove this assembly,
as it will be damaged during the removal process
andisnot available as a service part.Iftheheater
andthermostataredefective,replacetheentirepurge
valvehousingassembly whichincludestheseitems.

9
4. Remove the remaining six 3/8" cap screws (16), lock
nuts (19) and twelve special washers (17) that secure
theendcovertothehousing(24).Separatetheendcover
anddesiccantcartridge(22)fromthehousing(24).
5. Removethe end cover toouterhousingo-ring(23).
6. Donot remove the safety valve (12) from the end cover
unless it has been proven defective. If replacement is
required, apply thread sealant or Teflon®tape on the
threadsofthereplacement valve andtorqueto120-400
in. Ibs.
7. Place a strap or chain wrench around the desiccant
cartridge(22)so thatitis approximately2-3inchesaway
fromtheendcover.Rotatethecartridgecounterclockwise
until it completely separates from the end cover. Note:
Asubstantialtorque(upto50lb.ft.)mayberequiredto
perform this disassembly.
8. Removethe desiccantcartridgeo-ring(21) fromtheend
cover.
CLEANING & INSPECTION
1. Usingmineral spirits oranequivalentsolvent, clean and
thoroughly dry all metal parts.
2. Inspect the interior and exterior of all metal parts that
will be reused for severe corrosion, pitting and cracks.
Superficialcorrosionand/orpittingontheexteriorportion
oftheupperandlowerbodyhalvesisacceptable.
3. Inspect the bores of both the end cover and the purge
valvehousingfor deepscuffingorgouges.
4. Makecertain that allpurgevalvehousing andendcover
passagesareopenandfreeofobstructions.
5. Inspectthepipethreadsintheendcover.Makecertain
theyarecleanandfreeofthreadsealant.
6. Inspect the purge valve housing bore and seats for
excessivewearandscuffing.
7. Inspectthe purge valve piston seat forexcessivewear.
8. Inspect all air line fittings for corrosion. Clean all old
threadsealantfromthepipethreads.
9. All o-rings removed should be discarded and replaced
withnewo-ringsprovidedin appropriate kit(s).
Any component exhibiting a condition described in step 1
to 8 should be replaced.
ASSEMBLY
Priortoassembly,coatallo-rings,o-ringgrooves,and bores
with a generous amount of the lubricant included in the
maintenancekit. RefertoFigure7duringassembly unless
otherwiseadvised.
1. PurgeValveHousingAssembly
A. Installthequad-ring(14)initsgrooveon the O.D. of
thepurgepiston(10).Place the return spring (13)in
theboreof thepurgevalvehousing.Insert thepurge
piston (10) into the I.D. of the return spring. Place
the purge valve guide (2) onto the shoulder bolt (4)
followedbythepurgevalve(11). Usingaratchetor
wrench,screwthepurgevalve,purgevalveguideand
shoulderboltintothepurge housing until it bottoms.
This will require a tool to hold the top of the purge
pistonfrom rotating as the shoulder bolt is screwed
into the bottom of the purge piston to complete the
purgevalveassembly(8). Torque the shoulder bolt
to 60-90 in. lbs.
B. Install the o-rings (5, 6 and 7) on the purge valve
housingplacingeachinitsappropriatelocation.Note
o-ring(6)isnot used on DLUmodels. Iftheexhaust
coverwasremovedduringdisassembly,installiton
thepurgevalvehousingassembly(8)makingcertain
the“bubble”portionispositionedoverthethermostat.
Installtheassembledpurgevalvehousing (8) in the
end cover making certain to orient both parts such
that the connector is approximately 10 degrees
clockwisefromthesupply port,whilemakingcertain
the purge valve housing is fully seated against the
end cover. Secure the purge valve housing to the
end cover using the three 1/4" self-tapping screws
(3).Startallthreescrews by hand thentorqueto50-
80 in. Ibs.
2. Install the o-ring (1) on the check valve assembly (15),
then install the assembly in the end cover.
4
FIGURE 8 - END COVER TO HOUSING TORQUE PATTERN
78
3
5
62
1&9

10
3. Installthe desiccant cartridge o-ring (21)initsgroovein
theendcover.Usinga light coatoflubricant(includedin
kit), lubricate the bottom of the desiccant cartridge in
the area that will contact the o-ring (21) and end cover.
Screw the desiccant cartridge into the end cover until
contactismadebetween it andtheo-ring.Usingastrap
or chain wrench positioned 2-3" from the bottom of the
cartridge, turn the desiccant cartridge clockwise 180-
225 degrees beyond the position where initial contact
wasmadebetweenthecartridge and end cover o-ring.
Torque should not exceed 50 ft. Ibs.
4. Install the end cover outer housing o-ring (23) on the
shoulder in the end cover. Place the housing (24) over
the desiccant cartridge and align the holes. Install the
six3/8"capscrews(16),locknuts(19)andtwelvespecial
washers (17) making certain they are in the proper
positionasmarkedduringdisassembly.The two longer
3/8" cap screws (18) will be used to secure the AD-9™
air dryer to its mounting bracket. Tighten the six cap
screws and nuts in a star pattern in a fashion similar to
Figure 8; depending on lower bracket location. Torque
to 270-385 in. Ibs. (Refer to Fig. 8.) Note: The two
remaining bolt holes in the end cover and two 3/8" cap
screws must be the ones marked during disassembly
to assure proper orientation of the ports and adequate
length of the cap screws.
INSTALLATION
1. Install the assembled AD-9™air dryer back onto the
vehicle by slipping it into the upper mounting bracket.
Align the two unused holes in the end cover with the
bottom mounting bracket such that the bottom bracket
supports the air dryer. The AD-9™air dryer end cover
should rest on the bracket. Using the remaining two 3/
8" cap screws (18), four special washers (17), and two
locknuts(19),securetheairdryertothelowerbracket.
Tighten, then torque the two remaining cap screws to
270-385in.Ibs.
2. Tighten the 5/16" X 4-1/2" hex cap screw (25) and nut
(28)ontheuppermountingbracketsaddle(27)andstrap
(26).Torqueto80-120in. Ibs.
3. Reconnect the three air lines to the proper ports on the
endcover(identifiedduring disassembly).
4. Reconnect the vehicle wiring harness to theAD-9™air
dryer heater and thermostat assembly connector by
plugging it into the air dryer connector until its lock tab
snaps in place.
5. Before placing vehicle back into service, perform the
Operation and Leakage Tests stated elsewhere in this
manual.
RETROFITTING THE AD-9™AIR DRYER
GENERAL
Thefollowingretrofitinstructionsare presentedforreference
purposes only since Bendix aftermarket retrofit and
replacement air dryers are packaged with the most up-to-
dateinstallationinstructions.Theinstructionspackagedwith
the AD-9™air dryer should be followed in lieu of those
presentedhere.
Theprecedingportionof this manual dealswith“in-service”
repairand/orreplacementoftheAD-9™airdryer.Theportion
of the manual that follows is concerned with installing an
AD-9™air dryer on a vehicle not previously equipped with
one.
VEHICLE APPLICATION REQUIREMENTS
Thebasicapplication requirementspresentedhereapplyto
a standard air dryer installation. The majority of highway
vehicles in use today will meet these basic requirements
however,somemaynot.Examples of vehiclesthatmaynot
meet the requirements include, bulk trailer unloading
operationsandotherhighairconsumption/continuousflow
systems. While the AD-9™air dryer can be used on these
vehicles the standard installation procedure presented in
this manual may require modification to assure proper
operation and service life. Consult your local authorized
Bendix parts outlet or sales representative for additional
information.
1. ChargeCycleTime-TheAD-9™air dryerisdesignedto
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,dailyoperationthecompressorshouldrecover
fromgovernor“cut-in”to governor“cut-out”(usually100
psi to 120 psi) in 90 seconds or less at engine RPMs
commensuratewiththevehicle vocation.Iftherecovery
time consistently exceeds this limit, it may be
necessaryto“bypass”theair accessory responsible for
thehighair usage. Consultyourlocalauthorized Bendix
parts outlet or sales representative for additional
information.
2. PurgeCycleTime-Duringnormalvehicleoperation,the
aircompressormust remainunloadedfor aminimum
of 20 seconds for the standard AD-9™air dryer or 30
seconds for the Extended Purge model. These
minimum purge times are required to ensure complete
regenerationofthedesiccantmaterial. If the purgetime
is occasionally shorter than the times specified, no
permanentilleffectshould 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 - Brake systems that
incorporate compressors without integral unloading

11
LOCATING AD-9™AIR DRYER ON VEHICLE
1. TheAD-9™air dryer must be mounted vertically (purge
exhaust toward road surface) outside the engine
compartmentinanarea of air flowwhilethevehicleisin
motion. The AD-9™air dryer must not be exposed to
direct wheel splash (located behind axle mud flap is
acceptable).
2. Locate theAD-9™air dryer as close to the first (supply)
reservoiraspossible.
3. Do not locate theAD-9™air dryer near heat producing
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-9™airdryeron vehiclesothat aminimum
of 11 inches (28 cm) clearance below the end cover is
availabletoallowservicing.Alternatively,provide access
to the bracket bolts so the unit may be removed for
servicing.
5. Whenchoosing the mounting location for theAD-9™air
dryer,notethedischargelinelengthrequirementsstated
undertheheadingConnecting the AirLines,elsewhere
in this instruction sheet.
ImportantNote:Undernormaloperatingconditions,the
maximuminletairtemperature for theAD-9™airdryeris
160degreesFahrenheit.
MOUNTING THE AD-9™AIR DRYER
1. To install the lower mounting bracket on theAD-9™air
dryer,itwill be necessary to remove and discard two of
the end cover bolts and lock nuts.To determine which
end cover bolts to utilize to attach the lower bracket,
takeintoconsiderationthepipingconnectionsrequired
toinstalltheAD-9™air dryer andusethosethatwillbest
MOUNTING
BRACKET
SADDLE
mechanismsand/orutilizeacompressor discharge line
unloadervalvehavespecialAD-9™air dryer installation
requirements.ConsultyourlocalauthorizedBendixparts
outletorsalesrepresentativefor additional information.
4. AirCompressorSize-AlthoughtheAD-9™airdryercan
be used in conjunction with larger compressors, it was
designedprimarilyforunitsrated for up to 17 CFM. It is
recommendedthatwhenusingtheAD-9™airdryerwith
acompressorwhichhasarateddisplacementexceeding
17CFMthat anauthorizedBendixparts outletorBendix
marketingrepresentativebecontactedforassistance.
5. Holset“EorQE”TypeAirCompressors-Inorder for the
AD-9™airdryertofunctionproperlywheninstalledwith
the Holset Type “E or QE” compressor, several
specialized Holset components are required. Consult
your local authorized Holset parts outlet or sales
representativeforadditional information.
6. Use of Standard or Extended Purge AD-9™Air Dryer -
Usethefollowingguidelines:
Total Vehicle Reservoir
Volume Requirement
Less than 9,000 cu. in. ..................StandardAD-9™Air Dryer
9,000-12,500 cu. in. ...........................ExtendedPurgeAD-9™Air
Dryer
Greater than 12,500 cu. in. ............Contact Bendix Rep. or
Bendix Engineering
VEHICLE PREPARATION
1. Parkthevehicleonalevelsurfaceandpreventmovement
by means other than the brakes.
2. Drain all reservoirs to 0 p.s.i. (0 kPa).
2-1/8"
END
COVER
LOWER
BRACKET
EXTRA
LONG
BRACKET
CAP SCREW
←←
←←
←
←←
←←
←
SPECIAL
WASHER
FIGURE 9 - LOWER BRACKET INSTALLATION
FIGURE 10 - UPPER MOUNTING BRACKET AND STRAP
5/16" CAP
SCREW
MOUNTING
BRACKET STRAP
SLEEVE NUT
Change Image

12
position the unit for ease of installation. Locate the
bracket such that it cradles the end cover as shown in
Figure 9. Utilizing the two 2-3/8" long cap screws, lock
nuts and special washers provided with the AD-9™air
dryerretrofitunit, attachthelowermountingbracket and
torqueto 270-385 in. lbs.
2. Assemble the mounting strap and upper mounting
bracket as illustrated in Figure 10, by utilizing the 5/16"
capscrew(25)andsleevenut(28).
3. Place the upper bracket assembly onto the shell of the
AD-9™air dryer and orient it so that it bears entirely on
the cylindrical surface and does not extend onto the
domed top. The slot spacing between the upper and
lowerbracketshouldbeaminimum of 5.5 inches apart.
Do not tighten strap onto the shell at this time.
4. MounttheAD-9™airdryeron thevehicleusing3/8" bolts
(grade 5 min.) and washers. Torque to 25 ft. Ibs. (300
inchpounds.)After positioning and mounting the upper
bracket assembly according to the installation
requirements, torque the 5/16" nut to 80-120 in. Ibs. to
tighten strap onto the shell.
CONNECTING THE AIR LINES
PURGE CONTROL LINE
1. Install a purge control air line having a minimum inside
diameter of 3/16 inches between the AD-9™air dryer
end cover control port and an unused unloader port on
thegovernor.The control linemustbeplumbeddirect to
thegovernorandnotinserieswithautomaticdrainvalves,
lubrication systems, etc.
2. Thecontrollineshouldslopedownward totheend cover
withoutformingpotentialwatertraps.
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-9™air dryer discharge
contaminantsawayfromvehiclecomponentsitmaybe
necessary to purchase a special exhaust cover for the
AD-9™air dryer (Pc. No. 5003838). A one inch (25.4
mm)I.D.hosecanbeclampedon the specialAD-9™air
dryerexhaustcover.
FIGURE 11 - AD-9™AIR DRYER CHARGE CYCLE
COMPRESSOR
10 AMP - 12V
5 AMP - 24V SUP
CON
14 GA WIRE
TO IGNITION
& GROUND
SAFETY VALVE
DEL TO RESERVOIR
#2
RESERVOIR
#1
GOVERNOR
UNLOADER
PORT DELIVERY
SUPPLY
CONTROL
(HIDDEN)
FUSE

13
WIRING THE HEATER/THERMOSTAT
1. Determine the vehicle’s electrical system voltage and
make certain that the AD-9™air dryer that is to be
installed contains the same voltage heater. Use the
AD-9™airdryerpartnumbertoconfirmthepropervoltage.
The AD-9™air dryer is available with either a 12 or 24
voltheaterwhichuses75wattsof power.
2. Atwo lead, 12inch,wireharnesswithattached weather
resistant connector is supplied with all retrofit and
replacementAD-9™air dryers. Connect one of the two
leads of the wire harness to the engine kill or ignition
switch.Theremainingleadofthewireharness must be
connectedtoagoodvehicleground(not to the air dryer
or its mounting bracket). A fuse should be installed in
thepowercarryingwire;install a 10 ampfusefor12volt
heatersanda 5 amp fuse for a 24 volt heater.
3. Use 14 GA wire if it is necessary to lengthen the wire
harnessprovidedwiththeAD-9™airdryer.Makecertain
allwiresplicesarewaterproofed.
4. Tie wrap or support all electrical wire leading to the
AD-9™air dryerat6-8inchintervals.Note:Wiresshould
havesufficient slack and not completely taught.
TESTING THE AD-9™AIR DRYER
Beforeplacingthevehicleinservice,perform the following
tests:
1. Closeall reservoir drain cocks.
2. Build up system pressure to governor cut-out and note
that theAD-9™air dryer purges with an audible escape
ofair.
3. “Fan”the servicebrakestoreducesystemairpressure
togovernorcut-in.Notethatthesystemonceagainbuilds
to full pressure and is followed by a purge at theAD-9™
airdryerexhaust.
4. Itis recommended that the following itemsbetestedfor
leakagetoassurethattheAD-9™air dryer will not cycle
excessively.
(A) Total air system leakage (See Bendix publication
BW-5057“AirBrakeHandbook”).
(B) Compressorunloadermechanism.
(C) Governor.
(D) Draincockandsafetyvalveinfirst(supply)reservoir.
(E) All air connections leading to and from the first
(supply)reservoir.

14
AD-9™AIR DRYER TROUBLESHOOTING CHART
SYMPTOMS
1. Dryer is constantly
“cycling”orpurging.
Dryerpurgesfrequently
(every4 minutes or less
whilevehicle is idling).
A. If leakage IS SHOWN on gauges test for
excessiveservice brake system leakage.
Allowableleakage:
Pre-121 vehicles, single vehicles - 2 psi/
minute.
Tractor trailer - 3 psi/minute.
121vehicles, single vehicle - 1 psi/minute per
servicereservoir.
Tractortrailer - 3 psi/minute per service
reservoir.Repairand retest as required.
If leakage is NOT SHOWN on gauges test for
excessive supply system leakage.
A. Excessive system
leakage.IMPORTANT:
Notewhetherair
pressure loss is shown
ondashgauge(s).
Pressure loss shown on
gauges is caused by
servicebrake system or
componentleakage.
Pressureloss NOT
SHOWN on gauges is
caused by supply
system or component
leakage.
CAUSE REMEDY
Removedraincockorvalveinsupply reservoir (wet
tank) and install air gauge. Build system pressure,
allowairdryer to purge and observe air gauge in
supplyreservoir. Pressure drop should not exceed 1
psi per minute. Perform tests 1 to 6 in the order
presented.

15
AD-9™AIR DRYER TROUBLESHOOTING CHART
SYMPTOMS CAUSE REMEDY
1. Test fittings, hoses, lines and connections.
Apply soap solution to detect excessive
leakage.Tightenor replace as needed then
repeatthe air dryer charge-purge cycle and
observethe gauge installed in the supply
reservoir.Ifleakageiswithinlimitsremovegauge
fromreservoirandreplacedraincockor valve. If
excessive leakage is detected, continue testing.
2. Test accessories connected 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
pressureuntilairdryerpurgesandobserve
supplyreservoirgauge.Ifleakageis no longer
excessive,repair or replace leaking accessory. If
excessive leakage is detected, continue testing.
3. Test governor leakage. Build system pressure
togovernorcut-outturnoffengineandapply
soapsolution to governor exhaust port and
around cap. Leakage should not exceed a 1"
bubble in 5 seconds. Reduce system pressure
to 80 psi or less, and reapply soap solution.
Leakage should not exceed a 1" bubble in 5
seconds. If excessive leakage is detected in
eithertest,repairor replace governor.
4. Test compressor unloader leakage. Drain all
airpressurefrom system and remove the
governorfromthecompressor.Temporarilyplug
thegovernorunloaderportor air line that mated
with, or connected to, the compressor. Build air
system pressure until air dryer purges then
IMMEDIATELYSHUTOFFTHE ENGINE.
Observe the airgauge in the supplyreservoir. If
leakage is within limits, replace the compressor
unloaders.Reconnectthegovernortothe
compressor(afterremovingpluginstalledin
governor)andretestwhileobserving supply
reservoirgauge.Ifexcessiveleakageis
detected, continue testing.
5. Test air dryer purge valve and outlet
(delivery) check valve. Drain all air pressure
from system, remove the control line connection
at the air dryer and plug the end of the air line
leadingtothe governor (not the air dryer control
port).Build system pressure to governor cut-out
andobserveair gauge. If little or no pressure
dropis observed replace the air dryer check
valve.Ifpressuredropcontinuesapplysoap

16
solution to air dryer purge exhaust and purge
control port (where the control line was
removed).Leakage should not exceed a 1"
bubble in 5 seconds. If leakage is excessive
repairor replace purge valveassembly.
6. Withgaugeinstalled at RES port of governor,
pressureshouldnotdropbelow“Cut-In”pressure
atthe onset of the compressor “Unloaded”
cycle. If pressure drops, check for “kinks” or
restrictions in line connected to RES port. Line
connected to RES port on governor must be
samediameter,orpreferably larger than, lines
connectedtoUNLport(s) on governor.
B. With the supply port open to atmosphere, apply
120 psi at the control port.Apply a soap solution
tothe supply port and exhaust port (purge valve
seat area). Permissible leakage - 1" bubble in 5
seconds.
C. Test the Holset E Compressor unloader system
withfeedbacklineandcheckvalveforproper
operation. Make certain Holset ECON is not in
use with the drop-in version of the air dryer, if so,
removeandretest.
When installing a Bendix Drop-In air dryer in a
system equipped with a Holset E or QE
compressor,removetheHolsetECONvalvealong
withits feed back and governor control line.
AD-9™AIR DRYER TROUBLESHOOTING CHART
SYMPTOMS CAUSE REMEDY
B. Leakingpurgevalve
housingassemblyand/or
o-rings inAD-9™air dryer
endcover.
C. Holset “E” type
compressor.
Typical Drop-InAir Dryer End Cover
Check Valve
Feed Back Line

17
2. Water in vehicle
reservoir. A. Desiccantrequires
replacement-excessive
contaminantsin
desiccantcartridge
assembly.
B. Improperdischargeline
lengthorimproperline
material.Maximum air
dryerinlet temperature is
exceeded.
B. Refer to section entitled “Connecting theAir
Lines” as well asAppendixA, TableA columns
1 & 2 then check line size and length.
C. If system must have outside air fill provision,
outside air should pass through air dryer.This
practice should be minimized.
D. See Symptom #5.
E. Check causes and remedies for Symptom #1.
F. SeeAppendixA, TableA, column 1, for
recommendedcompressor sizes. If the
compressoris “too small” for the vehicle vocation
(forexample,whereavehicle’svocationhas
changedorservice conditions exceed the original
vehicleor engine OE spec’s) then upgrade the
compressor. Note:The costs incurred (e.g.
installing a larger capacity compressor, etc.) are
notcoveredunderoriginalcompressorwarranty.
Charge Cycle Time -TheAD-9™air dryer is
designedto 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
todetermine that during normal, daily operation
thecompressorshouldrecover from governor
“cut-in”to governor “cut-out” (usually 100 psi to
120 psi) in 90 seconds or less at engine RPM’s
commensuratewiththevehiclevocation. If the
recovery time consistently exceeds this limit, it
may be necessary to “bypass” the air accessory
responsiblefor the high air usage.An example of
where a by-pass system would be required is
when the compressor is used to pressurize a
tanktrailerforpurposesofoff-loadingproduct.
Consult your local authorized Bendix parts outlet
orsalesrepresentativeforadditionalinformation.
A. Replacedesiccant cartridge.
E. Purge(air exhaust) time
insufficientdueto
excessive system
leakage(seecauses for
Symptom #1).
C. Air system charged from
outsideair source
(outsideair not passing
throughairdryer).
D. Airdryernotpurging
(see Symptom #5).
AD-9™AIR DRYER TROUBLESHOOTING CHART
SYMPTOMS CAUSE REMEDY
F. Excessive air usage,
duty cycle too high - Air
dryernotcompatible
with vehicle air system
requirement(Improperair
dryer/vehicle
application).
NOTE: Duty Cycle isthe
ratio of time the compressor
spends building air to total
enginerunningtime.Air
compressorsaredesigned
tobuildair(run “loaded”) up
to 25% of the time. Higher
duty cycles cause
conditions that affect air
brakecharging system
performancewhichmay
requireadditional
maintenance. Factors that
add to the duty cycle are: air
suspension,additional air
accessories, use of an
undersizedcompressor,
frequentstops, excessive
leakagefromfittings,
connections, lines,
chambersorvalves,etc.

18
G. Aircompressor
dischargeand/orair
dryerinlettemperature
too high.
AD-9™AIR DRYER TROUBLESHOOTING CHART
SYMPTOMS CAUSE REMEDY
PurgeCycleTime-Duringnormalvehicle
operation, the air compressor must remain
unloaded for a minimum of 20 seconds for
the standard AD-9™air dryer or 30 seconds
for the Extended Purge Model. These
minimumpurge times are required to ensure
completeregeneration of the desiccant material.
If the purge time is consistently less than the
minimum, an accessory by-pass system must
be installed. Consult your local authorized Bendix
partsoutletorsales representative for additional
information.
European Air Brake Systems - Brake systems
thatincorporatecompressors without integral
unloadingmechanisms and/or utilize a
compressordischargelineunloader valve have
specialair dryer installation requirements.
Consult your local authorized Bendix parts outlet
orsalesrepresentativeforadditionalinformation.
Air Compressor Size -Although theAD-9™air
dryer can be used in conjunction with larger
compressors, it was designed primarily for units
rated for up to 17 CFM. It is recommended that
when using theAD-9™air dryer with a
compressor which has a rated displacement
exceeding 17 CFM that an authorized Bendix
partsoutletorBendix marketing representative
be contacted for assistance.
G. Restricted discharge line. SeeAppendixA,
TableA, column 1 & 2 for recommended sizes. If
discharge line is restricted or more than 1/16"
carbonbuild up is found, replace the discharge
line. Replace as necessary.
Discharge Line Freeze-Up. The discharge 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 information on
howtohelppreventdischargelinefreeze-ups,see
BendixBulletinsTCH-08-21and TCH-08-22. Shorter
dischargeline lengths or insulation may be required
in cold climates.
Insufficient coolant flow through compressor.
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.

19
AD-9™AIR DRYER TROUBLESHOOTING CHART
SYMPTOMS CAUSE REMEDY
Restricted air inlet (not enough air to
compressor). Checkcompressorairinlet line for
restrictions, brittleness, soft or sagging hose
conditions, etc. Repair as necessary. Inlet line size
is3/4 ID. Maximum restriction requirement for
compressors is 25 inches of water. Check the
engineairfilter and service if necessary (if possible,
check the air filter usage indicator).
Poorly filtered inlet air (poor air quality to
compressor).Checkforleaking,damagedor
malfunctioningcompressorairinletcomponents
(e.g. induction line, fittings, gaskets, filter bodies,
etc.). Repair inlet components as needed. Note:
Dirt ingestion will damage compressor and is not
coveredunderwarranty.
Ifyoufoundexcessiveoilpresent in the service
reservoirandyoudid not findanyissuesabove,the
compressor may be passing oil.
Replacecompressor.Ifstillunderwarranty,follow
normalwarrantyprocess.
H. Ifyou found excessiveoilpresentintheservice
reservoirandyoudidnotfind anyissuesabove,
the compressor may be passing oil. Test the
compressor using the BASIC cup method as
describedintheBendix compressor service
manualand referred to in Appendix A, Table A,
column 5.
Replacecompressor.Ifstillunderwarranty,follow
normalwarrantyprocess.
I. If vehicle uses Holset compressor, inspect
feedbackcheckvalveforproperinstallationand
operation.
When replacing the desiccant cartridge, make sure
desiccant cartridge assembly is properly installed
andsealingringsareinplaceonmountingsurface
ofdesiccantcartridge.
H. Compressormalfunction.
I. Air by-passes desiccant
cartridgeassembly.
Typical Drop-InAir Dryer End Cover
Check Valve
Feed Back Line

20
E. Excessivepressure
pulsationsfrom
compressor.(Typical
single cylinder type).
F. Governormalfunction.
Missing or restricted
governorcontrolline
installation.
5. Constantexhaustofair
atairdryerpurgevalve
exhaust.(Charge
mode.)
A. Airdryerpurgevalve
leakingexcessively.
B. Compressorfailsto
unload(stop
compressingair)andair
dryerpurgeexhaust
makes“sputtering”or
“popping”sound.
AD-9™AIR DRYER TROUBLESHOOTING CHART
SYMPTOMS CAUSE REMEDY
3. Oil present at air dryer
purgeexhaustor
cartridgeduring
maintenance.
J. Replace desiccant cartridge assembly. Refer to
AppendixA,TableAcolumns 3 & 4 for
recommendedintervals.
A. Airdryersremovewaterand oil from theair
brake charging system. A small amount of oil is
normal.Checkthat regular maintenanceisbeing
performed and that the amount of oil in the air
tanks(reservoirs) iswithintheacceptablerange
shown on the BASIC cup (see also column 5 of
Appendix A, Table A.) Replace the air dryer
cartridgeasneededandreturn thevehicleto
service.
A. Check to determine if air is reaching supply
reservoir. Inspectfor kinked tubing or hose.
Checkfor undrilled or restricted hose or tubing
fittingsand repair or replace as needed.
B. Verifyreliefpressure isatvehicleor component
manufacturerspecifications.Replaceif
malfunctioning.
C. Refer to Appendix A Table A and column 3.
Checkcompressorfor excessive oil passing
and/orcorrectcompressorinstallation.Repairor
replace as necessary. Replace desiccant
cartridge.
D. Test to determine if air is passing through check
valve.Repairorreplace.
E. Increasevolumeindischargelinebyincreasing
length or diameter. Add a ping tank (small
reservoir).
F. Testgovernoroperationand/orinspectthe
controllineleadingfromthegovernorUNL
(unloader)porttotheairdryercontrol port.
A. With compressor loaded, apply soap solution on
purgevalveexhaust,totest forexcessive
leakage.Repairpurgevalveasnecessary.
B. Confirmfailuretounload byincreasing&
decreasingengineRPMandnoting changein
the rate of leakage and intensity of
accompanyingleakagesound.Repair/replace
compressorunloaders.
J. Desiccant requires
replacement.
A. Airbrakecharging
system is functioning
normally.
A. Restrictionbetweenair
dryerandsupply(first)
reservoir.
4. Safetyvalve on air dryer
“poppingoff”or
exhaustingair.
B. Airdryersafetyvalve
malfunction.
C. Desiccantcartridge
maintenancerequired.
D. Malfunctioningdefective
dischargecheckvalvein
endcoveroftheAD-9™
airdryer.