Carrier 68RF50 Neoplan-LA Operation manual

T-271
Bus Air
Conditioning
Unit
Model
68RF50
NEOPLAN-LA

OPERATION AND
SERVICE MANUAL
Carrier Transicold Division, Carrier Corporation, P.O. Box 4805, Syracuse, N.Y. 13221
Carrier Corporation 1996 DPrinted in U. S. A. 0496
BUS AIR CONDITIONING UNIT
MODEL
68RF50
NEOPLAN-LA

i
TABLE OF CONTENTS
Section Page
1 DESCRIPTION 1-1.........................................................
1.1 Introduction 1-1............................................................
1.2 Refrigeration System Component Specifications 1-5..............................
1.3 Electrical Specifications 1-6...................................................
1.4 Safety Devices 1-6...........................................................
1.5 System Operating Controls and Components 1-7.................................
1.6 Reheat Coolant Valve 1-9....................................................
1.7 Liquid Line Solenoid Valve 1-9................................................
1.8 Moisture/Liquid Indicator 1-9.................................................
1.9 Heater Coolant Flow Cycle 1-9................................................
1.10 Refrigeration Flow Cycle 1-10..................................................
2OPERATION 2-1...........................................................
2.1 Starting And Stopping Instructions 2-1.........................................
2.2 Pre-Trip Inspection 2-1.......................................................
2.3 Unit Operation 2-1..........................................................
2.3.1 Cooling (Air Conditioning) Cycle Operation - Cycling Clutch Control 2-1...
2.3.2 Cooling (Air Conditioning) Cycle Operation - Reheat Control 2-2..........
2.3.3 Heat Operation 2-3..................................................
3 TROUBLESHOOTING 3-1...................................................
3.1 Unit Will Not Cool 3-1.......................................................
3.2 Unit Runs But has Insufficient Cooling 3-1......................................
3.3 Abnormal Pressure 3-1.......................................................
3.4 Abnormal Noise and Vibrations 3-2............................................
3.4.1 Abnormal Noise 3-2..................................................
3.4.2 Abnormal Vibration 3-2...............................................
3.5 Temperature Controller Malfunction 3-2........................................
3.6 No Evaporator Air Flow or Restricted Air Flow 3-3..............................
3.7 Expansion Valve Malfunction 3-3..............................................
3.8 No Heating or Insufficient Heating 3-3.........................................
4SERVICE 4-1...............................................................
4.1 Maintenance Schedule 4-1....................................................
4.2 Suction and Discharge Service Valves 4-1.......................................
4.3 Manifold Gauge Set 4-1......................................................
4.4 System Pumpdown 4-2.......................................................
4.5 Removing Refrigerant Charge 4-2.............................................
4.6 Refrigerant Leak Check 4-3...................................................
4.7 Evacuation and Dehydration 4-3..............................................
4.8 Adding Refrigerant to System 4-5..............................................
4.9 Checking Refrigerant Charge 4-5..............................................
4.10 Filter-Drier Removal 4-6.....................................................
4.11 Checking Pressure Switches 4-6................................................
4.12 Thermostatic Expansion Valve 4-7.............................................
4.13 Removing the Heater Coil 4-8.................................................
4.14 Replacement of Evaporator Coil 4-8...........................................
4.15 Servicing the Reheat Coolant Valve 4-9.........................................
4.16 Servicing the Liquid Line Solenoid Valve 4-10....................................

ii
TABLE OF CONTENTS (CONT’D)
Section Page
4 SERVICE (CONT’D) 4-1.....................................................
4.17 Removing the Condenser Fan Motor 4-10........................................
4.18 Servicing the Evaporator Fan Blower Motor Assembly 4-11.........................
4.19 Replacing the Return Air Filters 4-11...........................................
4.20 Compressor 4-11.............................................................
4.20.1 Replacing the Compressor 4-11.........................................
4.20.2 Checking the Compressor Oil Level 4-12.................................
4.20.3 Adding Oil to the Installed Compressor 4-12..............................
4.20.4 Adding Oil to Service Replacement Compressor 4-13.......................
5ELECTRICAL
5.1 Introduction 5-1............................................................
LIST OF ILLUSTRATIONS
Figure Page
1-1 Evaporator Assembly - Top View 1-2..........................................
1-2 Condenser Assembly - Top View 1-3..........................................
1-3 Electrical Control Panel Components for Models with Rotron Brushless Motors 1-4..
1-4 Reheat Coolant Valve 1-9...................................................
1-5 Heater Coolant Flow Diagram 1-9............................................
1-6 Refrigeration Cycle Diagram 1-10.............................................
2-1 Temperature Controller Sequence During Cooling Mode 2-2.....................
2-2 Temperature Controller Sequence During Cooling with Reheat Mode 2-2..........
2-3 Temperature Controller Sequence During Heating Mode 2-3.....................
2-4 Cooling Cycle - High Speed Vent Mode Operation 2-4..........................
2-5 High Speed Unloaded (2-cylinder operation) Cool Mode Operation 2-5............
2-6 High Speed Semi-loaded (4-cylinder operation) Cool Mode Operation 2-6.........
2-7 High Speed Fully Loaded (6-cylinder operation) Cool Mode Operation 2-7.........
2-8 High Speed Unloaded (2-cylinder operation) Cool with Reheat Mode Operation 2-8.
2-9 Heating Cycle - Low Speed Heat Mode Operation 2-9...........................
4-1 Suction or Discharge Service Valve 4-1........................................
4-2 Gauge Manifold Set 4-2....................................................
4-3 Evacuation Manifold 4-4....................................................
4-4 Evacuation Set-Up 4-5......................................................
4-5 Filter Drier Removal 4-6....................................................
4-6 Checking High Pressure Switch 4-6...........................................
4-7 Thermostatic Expansion Valve 4-7............................................
4-8 Thermostatic Expansion Valve Bulb and Thermocouple 4-8......................
4-9 Reheat Coolant Valve Assembly 4-9..........................................
4-10 Liquid Line Solenoid Valve - Alco 4-10.........................................
4-11 Compressor Oil Charge Connections 4-13......................................
4-12 Compressor - Model O5G 4-13...............................................
5-1 Electrical Wiring Schematic Diagram (68RF50 with Rotron Brushless Motors),
Dwg. No. C-070-935, Rev C 5-2.............................................

iii/iv
LIST OF TABLES
Table Page
1-1 Model Chart 1-1...........................................................
1-2 Additional Support Manuals 1-1.............................................
1-3 Safety Devices 1-6.........................................................
4-1 Pressure Switch Continuity Check 4-7.........................................
4-2 R-134a Temperature - Pressure Chart 4-14......................................

1-1
SECTION 1
DESCRIPTION
1.1 INTRODUCTION
Thismanualcontainsoperatingdata,electricaldata,
and service instructions for the 68RF50 NEOPLAN-LA
air conditioning, heating and ventilation systems shown
in the model chart below.
The68RF50unitsaretwopiecesystemsconsistingof
condenser and evaporator assemblies. The units are
installedontheroofofthebus.Theseunitsinterfacewith
the bus’ compressor,floorheater, and pumpto provide a
full air conditioning, heating and ventilation system.
The 68RF50 units are equipped with R-134a
refrigerant.
All control systems are powered by 24-vdc supplied
by the bus battery and alternator or alternate source.
Operation of the 68RF50 units is controlled
automatically by the temperature controller which
maintains the vehicles interior temperature at the
desired setpoint.
The units are equipped with a reheat/cycling clutch
switch to give the operator the option between cooling
control actions. In the cycling clutch control operation,
the compressor cycles on and off to control vehicle
interior temperature. When the switch is in REHEAT
position, the coolant valve opens and closes on
thermostat command to control vehicle interior
temperature while the air conditioning mode continues
to operate.
Table 1-2 shows additional manuals available for
servicing the 68RF50 units.
Table 1-1. Model Chart
MODEL SERIES DESCRIPTION
68RF50 NEOPLAN-LA Roof Mounted Three Condenser Fan
Table 1-2. Additional Support Manuals
MANUAL/FORM NO. EQUIPMENT COVERED TYPE OF MANUAL
T-199 05G Bus Compressor Operation and Service
T-200 05G Bus Compressor Parts List

1-2
123
4
5
6
7
891011
18
1213
14
15
16
17
1. Liquid Line Solenoid Valve
2. Thermal Expansion Valves
3. Hot Water Valve
4. Condenser Fan Switch
5. Evaporator Blower
6. Evaporator Blower Motor
7. Evaporator Blower
8. Heater Coil
9. Evaporator Coil
10. Sight Glass
11. Return Air Opening
12. Evaporator Coil
13. Heater Coil
14. Evaporator Blower
15. Evaporator Blower Motor
16. Evaporator Blower
17. Unloader Pressure Switch
18. Electrical Control Panel
(See Figure 1-3.)
Figure 1-1. Evaporator Assembly --- Top View

1-3
1. Receiver
2. Fusible Plug
3. Condenser Coil
4. Condenser Fan and Motor
5. DischargeLineValve
6. Discharge Check Valve
7. Ambient Air Switch
8. Filter-Drier Outlet Valve
9. Filter-Drier
10. Receiver Outlet or Filter-
Drier Inlet Valve
11. Sight Glass
Figure 1-2. Condenser Assembly --- Top View
12 3
4
5
6
7
8
9
10
11

1-4
1. Booster Pump Relay (BPR)
2. A/C Relay (ACR)
3. Heat Relay (HR)
4. Heat Relay #2 (HR2)
5. Fault Relay (FR)
6. Clutch Relay (CR)
7. Terminal Block “C” (TC)
8. Hourmeter (ACHM)
9. Rectifier #1 (REC1)
10. Rectifier #2 (REC2)
11. A/C Stop Relay (ACSR)
12. Low Voltage Cutout Device (LVCO)
13. Temperature Selector
14. Reheat/Cycle Switch (RHCS)
15. Circuit Breaker (CB9) --- 40 Amp
16. Circuit Breaker (CB8) --- 40 Amp
17. Circuit Breaker (CB7) --- 40 Amp
18. Circuit Breaker (CB6) --- 10 Amp
19. Temperature Sensor
20. Run Control Switch #1 (RCS1)
21. Circuit Breaker (CB3) --- 40 Amp
22. Circuit Breaker (CB2) --- 40 Amp
23. Circuit Breaker (CB1) --- 15 Amp
24. Evaporator Fan Relay #1 (EFR1)
25. Power Terminal Block (PTB)
26. Resistor #1 --- Evaporator (RES1)
27. Run Control Switch #2 (RCS2)
28. Evaporator Speed Relay #1 (ESR1)
29. Evaporator Speed Relay #2 (ESR2)
30. Condenser Fan Relay #1 (CFR1)
31. Condenser Speed Relay #1 (CSR1)
32. Resistor #2 --- Evaporator (RES2)
33. Terminal Block “B” (TB)
34. Resistor #3 --- Condenser (RES3)
35. Freeze Thermostat Switch (FTS)
36. Thermostat Controller (TH)
2345678 1011 121392021221816 19 231514
1
262728303132333435 2936
17
24
25
Figure 1-3. Electrical Control Panel Components for Models with Rotron Brushless Motors

1-5
1.2 REFRIGERATION SYSTEM COMPONENT
SPECIFICATIONS
a. Refrigeration Charge
R-134a:16lb.(7.3 kg)
b. Compressor
Model: 05G
No. of Cylinder: 6
Weight (Dry): 165 lbs. (75 kg),
including clutch
Oil Charge: 6.75 pints (3.2 liters)
Oil Level:
Old Crankcase (before S/N 4994J):
Bottom to 1/4 of sight glass
New Crankcase (beginning S/N 4994J):
Between Min---Max marks on crankcase
Approved Compressor Oils:
R-134a Unit:
Castrol: Icematic SW68C
Mobil: EAL Artic 68
ICI: Emkarate RL68H
c. Thermostatic Expansion Valve
R-134a TXV:
Superheat Setting: 6_F (-14.4_C) to 16_F
(-8.9_C), at 40_F
(4.4_C) evap. temp.
MOP Setting: 53.9 4psig
(3.8 0.28 kg/cm@)
d. Low Pressure Switch (LPS)
R-134a Unit:
Opens at: 10 3psig
(0.70 0.21 kg/cm@)
Closes at: 25 3psig
(1.8 0.21 kg/cm@)
e. High Pressure Switch (HPS)
R-134a:
Opens at: 425 10 psig
(30 0.7 kg/cm@)
Closes at: 300 10 psig
(21 0.7 kg/cm@)
f. Unloader Pressure Switch #2 (UPS2)
R-134a Unit:
Opens at: 40 5psig
(2.8 0.35 kg/cm@)
Closes at: 23 3psig
(1.6 0.21 kg/cm@)
g. Condenser Fan Speed Switch (CFS)
R-134a Unit:
Opens for high speed: 250 10 psig
(17.6 0.7 kg/cm@)
Closes for low speed: 190 15 psig
(13.4 1kg/cm@)
h. Low Ambient Switch (LATH)
Opens at: 45 5_F
(7.20.35_C)
Closes at: 55 5_F
(12.8 0.35_C)
i. Reheat Coolant Valve
Coil Voltage 24- vdc
MOPD: 35
Capacity: 10-GPM @
3psigαP

1-6
1.3 ELECTRICAL SPECIFICATIONS
a. Evaporator Blower Motor
Evaporator Motor Brushless
Bearing Lubrication Factory Lubri-
cated (addi-
tional grease
not required)
Horsepower 0.6
Full Load Amps (FLA) 20
Operating Speed (RPM) 2200
Voltage 27-vdc
Dropping Resistor 0.6-ohms
300-watts
b. Condenser Fan Motor
Condenser Motor Brushless
Bearing Lubrication Factory Lubri-
cated (addi-
tional grease
not required)
Horsepower 0.6
Full Load Amps (FLA) 19
Operating Speed (RPM) 1800
Voltage 27-vdc
Dropping Resistor 0.25-ohms
300-watts
1.4 SAFETY DEVICES
Safety devices protect system components from
damage caused by unsafe operating conditions.
If the High Pressure Switch (HPS) or Low Pressure
Switch (LPS) opens due to unsafe operating conditions,
the A/C operation willautomatically stop. The A/C stop
light will illuminate to indicate an unsafe condition has
occurred. The evaporatorblower motorswill continue to
run to circulate air throughout the bus.
During any mode of operation (A/C, Vent or Heat),
the evaporator or condensermotorswillstop if excessive
current draw is sensed by the circuit breakers. All circuit
breakers, when opened, must be manually reset by
depressing the breaker button.
When the High Pressure Switch (HPS) or Low
Pressure Switch (LPS) opens and unit operation stops,
place the driver’s A/C switch to the OFF position and
back to the ONposition to reset the A/C Stop Relay and
de-energize the stop light.
Table 1-3. Safety Devices
Unsafe Condition Safety Device Device Setting
1. Excessive current draw by the Circuit Breaker --- CB1 Opens at 15 amps
boost pump motor. Manual Reset
2. Excessive current draw by Circuit Breaker --- CB2 Opens at 40 amps
evaporator blower motor no. 2. Manual Reset
3. Excessive current draw by Circuit Breaker --- CB3 Opens at 40 amps
evaporator blower motor no.1. Manual Reset
4. Excessive current draw by clutch. Circuit Breaker --- CB6 Opens at 10 amps
Manual Reset
5. Excessive current draw by Circuit Breaker --- CB7 Opens at 40 amps
condenser motor no.1. Manual Reset
6. Excessive current draw by Circuit Breaker --- CB8 Opens at 40 amps
condenser motor no. 2. Manual Reset
7. Excessive current draw by Circuit Breaker --- CB9 Opens at 40 amps
condenser motor no. 3. Manual Reset
8. High system pressure. High Pressure Switch (HPS) Opens at 425 10 psig
Automatic reset (30 0.7 kg/cm@)
9. Low system pressure Low Pressure Switch (LPS) Opens at 10 3psig
Automatic Reset (0.70 0.21 kg/cm@)

1-7
1.5 SYSTEM OPERATING CONTROLS AND
COMPONENTS
a. Temperature Controller (Thermostat)
The Temperature Controller is a thermostat that
senses and controls the vehicle interior air temperature.
The desired interior temperature, setpoint of the
controller is manually set with the temperature selector
which is located in the electrical control panel. (See
Figure 1-3.) The controller’s temperature sensor
monitors the bus’ interior temperature at the return air
sectionof theunitandcontrolstheoperatingfunctionof
the system to maintain setpoint.
The controller regulates the operation cycles of the
unit with four interior relays which activate the cool or
heatandunloadedorloadedfunctionsofthesystem
relative to deviations from the thermostat setpoint. One
relay controls the operation of Unloader Valve #1
(UV1). Another relay controls the function of Unloader
Valve #2 (UV2). Another activates the cool cycle and
another relay activatesthe heat cycle. Refer to Section 2
for description of operational control sequences for the
various operational modes of operation.
b. Manual Switches
A/C Switch (ACS)
The A/C Switch (ACS) selects the Cooling (Air
Conditioning)orHeatingmodeofoperation.Thisswitch
is located on the driver’s control panel. The switch is
placed in the COOL position to energize A/C Relay
(ACR) for cooling mode of operation and in the HEAT
position to energize the Heat Relay (HR) for heating
mode.IntheCOOLor HEATposition,andwiththeRun
Control Switches (RCS1 and RCS2) in the ON position,
24-voltsisalsosuppliedtoterminalboardTC,terminal
no. 8.
Reheat/Cycle Switch (RHCS)
TheReheat/CycleSwitch(RHCS)allowsoperatorto
selecteitherreheatorcyclingclutchcontrolaction.When
placed in the CYCLING position, the unit cycles in the
cooling mode of operation. When in the REHEAT
position, unit cycles from cooling only mode to cooling
with reheat mode.
Run Control Switch (RCS)
One Run Control Switch (RCS1) is located in the
electrical control panel in the return air opening of the
unit and the other (RCS2) is located on top of the
electricalpanel,whichisaccessedthroughtheevaporator
coveronthebusroof.Theseswitches,whenplacedinthe
OFF position, will prevent the unit from starting when
servicing the unit and when placed in the ON position,
allowspowertobeappliedtotheTerminalBlock(TC)for
operation of the control system for heating, cooling or
cooling with reheat modes of operation.
c. Thermal Switches
Low Ambient Thermostat (LATH)
TheLowAmbientThermostat(LATH)monitorsthe
vehicles outside temperature. The switch opens a set of
contacts at 45 5_F (7.2 0.35 _C) and closes at 55
5_F(12.80.35_C).Whentheoutsidetemperatureis
belowtheopensettingoftheswitch,theswitchopensthe
circuit to disengage the clutch and stop the compressor
andstopthecondenserfans.
d. Pressure Switches
Condenser Fan Speed Switch (CFS)
The Condenser Fan Speed Switch (CFS) senses
refrigerantdischargepressureandcontrolcondenserfan
speed. If refrigerant discharge pressure rises to the CFS
cutout setting, the switch will open to de-energize the
Condenser Speed Relay (CSR); this will close a set of
normallyclosedCSR1 contactsandcause theCondenser
FanMotors (CM1, CM2 and CM3)to run at highspeed.
When the pressure drops to the CFS cut-in setting, the
switch will close to energize CSR, which will open the
CSR1 contacts and cause the Condenser Fan Motors
(CM1, CM2 and CM3) to run at low speed. Refer to
paragraph 1.2 for switch settings.
Unloader Pressure Switch #2(UPS2)
The Unloader Pressure Switch #2 (UPS2) controls
unloader operation during the cooling mode of
operation. The switch closes on a drop in evaporator
suction pressure to energize Unloader Valve #1 (UV1).
Energizing UV1 will place the compressor in four
cylinder ( semi-loaded) operation. As pressure rises, the
switch will re-open. Refer to 1.2 for switch settings.
e. Relays
Fault Relay (FR)
The Fault Relay (FR) is located in the electrical
control panel. The FR relay is energized during initial
start-up,throughtheclosedcontactsoftheHighandLow
PressureSwitches(HPSandLPS),toactivatethecooling
circuit components. If the High or Low Pressure Switch
(HPS or LPS) opens during normal operation due to
unsafe operating conditions, the Fault Relay (FR) will
de-energize and open a set of normally open contacts to
deactivate the cooling circuit control components.
Another set of normally closed FR contacts will close to
energize the relay A/C Stop Relay (ACSR), which closes
a set of normally open contacts to light the stop light.
A/C Stop Relay (ACSR)
The A/C Stop Relay (ACSR) is located in the
electrical control panel. The ACSR is a time delay relay
which illuminates the stop light when energized by the
Fault Relay (FR).
Torestarttheunitandturnthestoplightoff,theA/C
Switch (ACS) must be toggled to OFF and then to
COOL.

1-8
Clutch Relay (CR)
The Clutch Relay (CR) is located in the electrical
control panel. When the CR relay is energized, a set of
internal contacts will close to engage the compressor
clutch (CL) to start the refrigerant cycle.
Air Conditioning Relay (ACR)
The Air Conditioning Relay (ACR) is located in the
electrical control panel. The ACR relay is energized
when the A/C Switch (ACS) is placed in the COOL
position. When the ACR relay is energized, a set of
normally open ACR contacts will close to allow the
ClutchRelay (CR) andCondenser Fan Relay (CFR1)to
energize.Whende-energized,theACRrelaywillprevent
the clutch and condenser fans from being activated
during the heating mode of operation.
Heat Relay (HR)
The Heat Relay (HR) is located in the electrical
controlpanel. This relay willenergize onlywhen theA/C
Switch (ACS) is in the HEAT position. When energized,
a set of normally open HR contacts will close to allow the
thermostattocontroloperationoftheBoostPumpRelay
(BPR) and Reheat Coolant Valve (RCV) during the
heating mode. When the thermostat calls for heating,
power is applied from thermostat plug J1, pin 1, through
theclosedHRcontactstoenergizetheBoostPumpRelay
(BPR) and Reheat Coolant Valve (RCV) and start the
flow of engine coolant for heating.
Heat Relay #2 (HR2)
TheHeatRelay#2(HR2)islocatedin theelectrical
control panel. This relay is energizedduring thecooling
cycle mode (when the thermostat is calling for cooling)
and during the cooling with reheat mode (when the
thermostat is calling for cooling only) to prevent the
heating circuit from being energized while in cooling
operation. The relay is de-energized during the cooling
with reheat mode to activate the heating control circuit
when the thermostat is not calling for cooling.
With the ACS switch in the COOL position andthe
RHCS switch in the CYCLE or REHEAT position, and
when the thermostat calls for cooling, power is applied
from the thermostat plug no. J1, pin no. 3, to energize
Heat Relay #2 (HR2). Energizing relay HR2 opens a set
of normally closed HR2 contacts to prevent activationof
theheatingcontrolcircuitwhileunitisinthecoolingcycle
mode.
With the ACS switch in the COOL position andthe
RHCS switch in the REHEAT position, and when the
thermostat is not calling for cooling, power is removed
from thermostat plug J1, pin no. 3, to de-energize Heat
Relay#2(HR2).De-energizingrelayHR2closesasetof
normally closed HR2 contacts to activate the heating
control circuit enabling the system to provide heating
during the cooling with reheat mode.
Evaporator Fan Relay #1 (EFR1)
Evaporator Fan Relay #1 (EFR1) is located in the
electrical control panel. When the Air Conditioning
Switch (ACS) is placed in either the COOL or HEAT
position,EFR1relay isenergized. Whenenergized, aset
of internalEFR1 contacts are closed to start Evaporator
Fan Motors (EM1 and EM2).
Evaporator Speed Relays #1 and #2 (ESR1 and ESR2)
TheEvaporatorSpeedRelays(ESR1andESR2)are
located in the electrical control panel. These relays will
onlyenergizewhentheA/CSwitch(ACS)isintheHEAT
position. When energized, normally closed ESR1 and
ESR2contactswillclosetostartlowspeedevaporatorfan
motor operation.
Condenser Fan Relay #1 (CFR1)
The Condenser Fan Relay #1 (CFR1) is located in
the electricalcontrolpanel. When theA/C Switch(ACS)
is placed in the COOL position, A/C Relay (ACR) is
energized closing a set of normally open ACR1 contacts.
And, when the thermostat calls for cooling, power is
applied to thermostat plug J1, pin no. 3, to energize
CFR1 relay through the closed ACR1 contacts. When
energized,a setof normally open CFR1contacts closeto
start the Condenser Fan Motors (CM1, CM2 andCM3).
The Low Ambient Thermostat (LATH) and Freeze
Thermostat Switches (FTS), if installed, must also be
closed to energize the Condenser Fan Relay.
Condenser Speed Relay (CSR)
TheCondenserSpeed Relay(CSR) islocated inthe
electrical control panel. This relay is energized at the
same moment the Condenser Fan Relay is energized
provided the Condenser Fan Speed Switch (CSR) is
closed.Whenenergized,the CSRrelay will opena set of
normally closed CSR1 contacts to operate condenser
fansonlowspeed. If thecondensercoilpressurereaches
theCFSswitchcutoutsetting,theCFSswitchwillopento
de-energize the Condenser Speed Relay (CSR).
De-energizing the CSR relay will close a set of normally
closed CSR1 contacts enabling the Condenser Fan
Motors(CM1,CM2andCM3)tooperateonhighspeed.
Boost Pump Relay (BPR)
The Boost Pump Relay (BPR) is located in the
electrical control panel. This relay is energized during
heating. When the Boost Pump Relay (BPR) is
energized,asetofnormalopenBPRcontactswillcloseto
activate the Boost Pump Motor (BPM).
Low Voltage Cutout (LVCO)
The Low Voltage Cutout (LTCO) is located in the
electrical control panel.If thisrelay detects a lowvoltage
condition, LVCO contacts will open to de-energize
Clutch Relay (CR), which disengages the clutch.

1-9
1.6 REHEAT COOLANT VALVE
The Reheat Coolant Valve (RCV) is located in the
evaporatorsectionoftheunitontheroofofthebus.(See
Figure1-1.)Thevalveisanelectrically operatedsolenoid
valve controlled by thermostat command. The RCV
controls the coolant flow to the heater coil during
heating.Thevalveisnormallyclosedandopenswhenthe
coilisenergized,andcloseswhenthecoilisde-energized.
Whenthe thermostat calls for heating, the RCV coil
is energized, the plunger is lifted and the pilot port is
opened to relieve the pressure on top of the diaphragm.
Now the valve inlet pressure will act on the bottom
portion of the diaphragm, lifting the diaphragm to open
the main port. Once the port is open, the diaphragm is
held off the seat by the pressure difference across the
port. When the coil is de-energized, the plunger drops
due to the kick-off spring and the pilot port closes. The
pressure above the diaphragmisno longervented to the
downstream side of the valve and the diaphragm drops,
closing the main port.
The valve’s Maximum Operating Pressure
Differential (MOPD) is 35. The MOPD is the maximum
pressure differential against which the solenoid will
open. The valve has a 10 gallon per minute minimum
capacity with a 3 psig pressure differential across the
valve.
1
2
3
4
5
6
7
8
910
11
12
1. Valve Body
2. Equalizer Port
3. O-Ring
4. Closing Spring
5. Plunger
6. Kick-Off Spring
7. Coil
8. Coil Housing
Assembly
9. Coil Retaining
Screw
10. Nameplate
11. Diaphragm
12. Pilot Port
Figure 1-4. Reheat Coolant Valve
INLET
PORT OUTLET
PORT
1.7 LIQUID LINE SOLENOID VALVE
The Liquid Line Solenoid Valve (LLS) is located in
the evaporator section of the unit on the roof of the bus
(SeeFigure 1-1.)Theelectricallyoperatedsolenoidvalve
is energized when the Clutch Relay (CR) is energized.
The liquid line solenoid valve controls the flow of the
refrigerant to the expansion valve during cooling (air
conditioning) mode. The valve is normally closed and
openswhenthecoilisenergize,andcloseswhenthecoilis
de-energized.
1.8 MOISTURE/LIQUID INDICATOR
The moisture indicator is located on the liquid line
betweentheliquidlinesolenoidandtheexpansionvalve.
The element in the indicator is highly sensitive to
moistureandwillgraduallychangecolorindirectrelation
to an increase ordecrease in the moisture content of the
system.Thedry-caution-wetsystemoperatingconditions
aretheneasilydeterminedbymatchingtheelementcolor
with the four colors displayed on the reference label.
Colors change as often as the system moisture content
changes.
1.9 HEATER COOLANT FLOW CYCLE
Heating is controlled by the thermostat which
controls the operation of the Reheat Coolant Valve
(RCV).Whenthecoolantvalvesolenoidisenergized,the
valve will open to allow engine coolant to flow through
the heater coil. Refer to section 2.3.3 for control
operation.
At the same time the coolant valve is energized, the
boost pump (customer supplied) isactivated to circulate
theenginecoolantthroughtheinlettubeandheader
hose to the heater coil. The coolant exits the coil and
flowsthroughthevalveinlethose.Withthecoolantvalve
opened, coolant flows through the valve outlet and
coolantoutlettubebacktotheengine.
1
3
42
1. Heater Coil
2. Reheat Coolant Valve
3. Coolant Inlet Tube
4.CoolantOutletTube
Figure 1-5. Heater Coolant Flow Diagram

1-10
1.10 REFRIGERATION FLOW CYCLE
Figure 1-6. Refrigeration Cycle Diagram
123
4
567 8
9
11
12
13
14
16
18
19
20
10
15
1. Evaporator Coils
2. Inline Sight Glass
3. Low Pressure Service Port
4. Expansion Valves
5. Filter-Drier Outlet Valve
6. Filter-Drier
7. Filter-Drier Inlet Valve
8. Receiver
9. Condenser Coils
10. Discharge Service Valve
11. Suction Service Valve
12. Discharge Check Valve
13. DischargeLineValve
14. Discharge Line
15. Suction Line
16. Unloader Pressure Port 2
17. Unloader Pressure Port 3
18. Condenser Fan Pressure Port
19. High Pressure Service Port
20. Liquid Line Solenoid Valve
21. Optional Suction Gas to
Liquid Line Heat Exchanger
21 OPTIONAL
17
The refrigeration system contains R-134a
refrigerant. The refrigeration cycle is the same for air
conditioning and heating (during reheat mode). The
refrigerantcycleisoffduringtheventonlymode,onlythe
evaporator blowers operate to circulate air throughout
the bus.
The refrigeration cycle begins when the compressor
clutch is engaged. The compressor raises the pressure
and the temperature of the refrigerant and forces itinto
the condenser tubes. The condenser fan circulates
surroundingair(whichisata lowertemperaturethanthe
refrigerant) over the outside of the condenser tubes.
Heat is transferred from the refrigerant (inside the
tubes) to the condenser air (flowingover the tubes). The
condenser tubes have fins designed to improve the
transfer of heat from the refrigerant gas to the air. This
removal of heat causes the refrigerant to liquefy. The
liquid refrigerant leaves the condenser and flows to the
receiver.
The receiver serves as a liquid refrigerant reservoir
so a constant supply of liquid is available to the
evaporator as needed and as a storage space when
pumpingdownthesystem.Thereceiverisequippedwith
a sight glass to check for the correct refrigerant level.
Therefrigerantleavesthereceiverandflowsthrough
thefilter-drierinletservicevalvetothefilter-drier,which
contains an absorbent for keeping the refrigerant clean
and dry. The refrigerant flow continues through a
filter-drier outlet service valve.
The liquid refrigerant then flowsthrough a normally
closed liquid line solenoid valve. When the compressor
clutchisengaged,24-voltsisalsoappliedtotheliquidline
solenoid valve coil opening the valve and allowing liquid
to flow.
The liquid refrigerant then flows through an
externally equalized thermostatic expansion valves,
whichreducesthepressureandtemperatureoftheliquid
and meters the flow of liquid refrigerant supplied to the
evaporator coil to maximum use of the evaporator heat
transfer surface.
Thelowpressure, lowtemperatureliquidrefrigerant
that flowsinto the evaporator tubesis colderthan the air
circulatingovertheoutsideoftheevaporatortubesbythe
evaporator blowers. Heat is transferred from the
evaporatoraircirculatingovertheoutside oftubestothe
liquid refrigerant flowing inside the tubes. The
evaporator tubes have aluminum fins to increase heat
transfer from the air to the refrigerant. The resultant
coolerairisthencirculatedthroughouttheinteriorofthe
bus.
The transfer of heat from the air to the low
temperature liquid refrigerant in the evaporator causes
the liquid to vaporize. This low temperature, low
pressurevaporpassesthroughthesuctionlinebacktothe
compressor where the cycle is repeated.

2-1
SECTION 2
OPERATION
2.1 STARTING AND STOPPING INSTRUCTIONS
a. Starting
1. Start the vehicle engine.
2. Switch the driver’s A/C Switch (ACS) to the
desired mode of operation (COOL or HEAT position).
NOTE
The Run Control Switches (RCS1 and RCS2),
one located in the return air opening and one
located on top of the evaporator section below
the lid, must be in the ON position to start unit
operation.
b. Stopping
1. Switch the driver’s A/C Switch (ACS) to the OFF
position. NOTE
Besureairconditioningunitis turnedoffbefore
stopping the engine.
2.2 PRE-TRIP INSPECTION
After starting unit, allow system to stabilize (10 to 15
minutes) and proceed as follows:
1. Listen for abnormal noises.
2. Check compressor oil level.
3. Check refrigerant level.
4. Check moisture-liquid indicator.
2.3 UNIT OPERATION
The desired COOL or HEAT position for cooling or
heating mode of operation is selected manually on the
A/C Switch (ACS) located on the driver’s switch panel.
The selection of CYCLING (Clutch) or REHEAT
cooling control is selected manually on theReheat/Cycle
Switch located on the unit’s controlpanel on the roof of
the vehicle. When a mode of operation is selected, the
Electronic Thermostat(TH) sensesthe vehicle’sinterior
temperature and automatically controls the system to
maintain the desired temperature setpoint.
The cycling clutch and reheat control actions are
functional only during operation of the cooling cycle
(when the A/C Switch is set to the COOL position).
When the A/C Switch is in the HEAT position, the A/C
Relay (ACR) is de-energized, opening the circuit to the
cooling control components.
Theunitcontrolcircuitoperateson24-volts supplied
by the bus battery or alternator.
2.3.1 Cooling (Air Conditioning) Cycle Operation ---
Cycling Clutch Control (See Figure 2-1.)
To operate in cycling clutch mode of operation, the
Reheat/Cycling Switch (RHCS) is placed in the CYCLE
position. In this position, the thermostat cycles the
compressor on and off to control vehicle interior
temperature.
When the driver’s A/C Switch (ACS) is placed in the
COOL position and the thermostat iscalling forcooling,
the air conditioning (cooling) circuit is activated. With
theswitchinthisposition,24-volts issuppliedtotheA/C
Relay (ACR), which closes a set of normally open
(ACR1) contacts to activate the cooling control circuit
components. Voltage is also applied to the Run Control
Switches (RCS1 and RCS2). With these switches in the
ON position, voltage is also applied to energize Fault
Relay (FR), Evaporator Fan Relay (EFR1) and Low
Voltage Cutout relay (LVCO). Energizing the
Evaporator Fan Relay closes normally open EFR1
contacts to start high speed evaporator fan operation
through the normally closed ESR1 and ESR2 contacts.
During the cooling mode, the evaporator fans always
operate on high speed. During the heating mode, the
evaporator fans always operate on low speed.
Energizing the Fault Relay closes a set of normally
open FR contacts to apply power to activate the cooling
control circuit and, provided there is no high or low
pressure refrigerant condition, opens the circuit to the
stop light. The Low Voltage Cutout Relay senses circuit
control voltage and de-energizes to open normally open
LVCO, contacts, which de-energizes the Clutch Relay
(CR) when a low voltage condition occurs. Voltage is
also applied to Electronic Thermostat (TH), pin no. 4,
and one REHEAT terminal of the Reheat/Control
Switch(RCHS).Applyingpowertothethermostatallows
it to automatically select heating or cooling and
unloaded, semi-loaded or fully loaded compressor
operation to maintain bus interior temperature.
When the vehicle’s interior temperature rises to
+1˚F above the thermostat setpoint, the thermostat
switches from high speed vent operation to high speed
unloaded (2-cylinder) cool operation. During the high
speed vent mode (See Figures 2-1 and 2-4.), the
thermostat de-activates the cooling circuit by removing
power from thermostat plug J1, pin no. 3. The
evaporator fans continue to operate on high speed to
circulate air within the bus.
In the high speed unloaded cool mode (See Figures
2-1 and 2-5.), the thermostat switches to the cool
position, applyingpowertothermostatplugJ1,pinno.3;
this energizes the Clutch Relay (CR), Condenser Speed
Relay(CSR) andCondenser FanRelay (CFR1) through
the closed ACR1 and LVCO contacts. Energizing the
Clutch Relay (CR) closes a set of normally open CR
contacts , which activates the refrigerant control circuit,
through the closed FR and ACSR contacts, to start the
refrigerant flow cycle. Energizing the Condenser Fan
Relay (CFR1) closes a set of normally open CFR1
contacts, which applies power to start Condenser Fan
Motors (CM1, CM2 and CM3). Energizing Condenser

2-2
Speed Relay (CSR) opens a set of normally closed
contacts toswitchtolowspeedcondenserfanoperation.
At this point, the thermostat also applies power to plug
J1,pinno.6 andpinno.5toenergize UnloaderValves#1
and #2 (UV1 and UV2), which unloads two banks of
compressor cylinders . The compressor now operates in
unloaded (2-cylinder) cool mode.
When the vehicle’s interior temperature rises to
+3˚F above the thermostat setpoint, the thermostat
switches from high speed unloaded (2-cylinder) cool
operation to high speed semi-loaded (4-cylinder) cool
operation.Inthesemi-loadedcoolmode(SeeFigures2-1
and 2-6.), the thermostat removes power from plug J1,
pin no. 6., whichde-energizes UnloaderValve #1(UV1)
to load two additional compressor cylinders. The
compressor now operates in semi-loaded (4-cylinder)
cool mode. However, Unloader Pressure Switch (UPS2)
can override the thermostat demand for semi-loaded
operation by closing a set of contacts to energize
Unloader Valve UV1, unloading a bank of compressor
cylinders when refrigerant suction pressure drops below
its setpoint.
When the vehicle interior temperature rises to +5˚F
above the thermostat setpoint, the thermostat switches
from high speed semi-loaded cool operation to high
speedfullyloadedcool operation.Inthe highspeed fully
loaded cool mode (See Figures 2-1 and 2-7), the
thermostat removes power from plug J1, pin no. 5,which
de-energizes Unloader Valve #2 (UV2) to load the two
remaining compressor cylinders. The compressor now
operates in fully loaded (6-cylinder) cool mode.
On a falling temperature, the controller sequence
changes in reverse to the above. See Figure 2-1 for
controller sequence on falling temperature.
2.3.2 Cooling (Air Conditioning) Cycle Operation --- Re-
heat Control (See Figure 2-2.)
When the vehicle interior temperature falls to -1˚F
below the thermostat setpoint and the Reheat/Cycle
Switch (RHCS) is set to the REHEAT position, the
thermostat switches from cooling only operation to
cooling with reheat. (See Figures 2-2 and 2-8.) Under
normalconditions (i.e.,withACR,LATH,FTS,CFSand
LVCO contacts closed), and with the ACS switch in the
COOL position and the RHCS switch in the REHEAT
position, the cooling circuit is always energized (i.e.,
clutch relay and condenser fans are energized). In this
mode, the thermostat cycles the reheatcontrolcircuit to
maintain vehicle interior temperature. When reheat is
required on a falling temperature, at -1˚Fbelowthe
setpoint,thethermostatremovespowerfrom plugJ1,pin
no. 3, which de-energizes Heat Relay #2 (HR2) to close
normally closed HR2 contacts and energize Reheat
Coolant Valve (RCV) solenoid and Boost Pump Relay
(BPR); this activates the reheat control circuit.
Energizing the Boost Pump Relay closes normally open
BPR contacts to start the Boost Pump Motor (BPM).
Energizing the reheat coolant valve solenoid coil opens
the valve allowing flow of engine coolant to the heater
coil for heating.
On a rising temperature to +1˚Fabovethe
thermostat setpoint, the thermostat switches from high
speed cool with reheat to high speed cool only mode.
Figure 2-1. Temperature Controller Sequence
During Cooling Mode
FALLING
TEMPERATURE
RISING
TEMPERATURE
1˚FABOVE
SETPOINT
SETPOINT SETPOINT
3˚FABOVE
SETPOINT
HIGH SPEED VENT
HIGH SPEED
FULLY LOADED
COOL 5˚FABOVE
SETPOINT
3˚FABOVE
SETPOINT
1˚FABOVE
SETPOINT
-1˚FBELOW
SETPOINT
HIGH SPEED,
SEMI-LOADED
COOL
HIGH SPEED
UNLOADED
COOL
Figure 2-2. Temperature Controller Sequence
During Cooling with Reheat Mode
FALLING
TEMPERATURE
1˚FABOVE
SETPOINT
SETPOINT SETPOINT
3˚FABOVE
SETPOINT
HIGH SPEED
FULLY LOADED
COOL 5˚FABOVE
SETPOINT
3˚FABOVE
SETPOINT
1˚FABOVE
SETPOINT
HIGH SPEED,
SEMI-LOADED
COOL
HIGH SPEED
UNLOADED
COOL
RISING
TEMPERATURE
HIGH SPEED
UNLOADED
COOL WITH
REHEAT
-1˚FBELOW
SETPOINT

2-3
2.3.3 Heat Operation (See Figure 2-3.)
Thedriver’sA/CSwitch(ACS)isplacedin theHEAT
position toactivate the heatingcycle. With this switchin
the HEAT position, 24-vdc is applied to energize Heat
Relay (HR) and Evaporator Speed Relays (ESR1 and
ESR2). Energizing the Heat Relay (HR) closes a set of
normallyopenHRcontacts,whichallows thethermostat
to energize Boost Pump Relay (BPR) and Reheat
Coolant Valve (RCV) upon a demand for heating.
Energizing Evaporator Speed Relays (ESR1 and ESR2)
opens normally open ESR1 and ESR2 contacts to start
lowspeedevaporatorfanoperationprovidedEvaporator
Fan Relay (EFR1) is energized. Energizing Boost Pump
Relay (BPR)closes normallyopenBPRcontactstostart
Boost Pump Motor (BPM). Energizing Reheat Coolant
Valve(RCV)opensthevalveandstartstheflowofengine
coolant through the heating coils for heating.
When the ACS switchis in the Heat position, power
isalsosuppliedtoRunControlSwitch(RCS1). WithRun
Control Switches (RCS1 and RCS2) in the ON position,
power is applied through the Run Control Switches to
energize Fault Relay (FR), Evaporator Fan Relay
(EFR1) and Low Voltage Cutout Relay (LVCO).
Energizing the Fault Relay closes a set of normally open
FR contacts in the cooling control circuit and, provided
there is no high or low pressure refrigerant condition,
opens the circuit to the stop light. The Low Voltage
Cutout Relay senses circuit control voltage and
de-energizes to open normally open LVCO contacts to
de-energize theClutchRelay(CR)duringcooling,when
a low voltage condition occurs.
When the vehicle interior temperature falls to -2˚F
below the thermostat setpoint, the thermostat switches
from low speed vent to low speed heat mode. (See
Figures2-3and2-9.)Inthismode,thethermostatapplies
powertoplugJ1,pinno.1,toenergizeBoostPumpRelay
(BPR) and Reheat Coolant Valve (RCV) through the
closed HR contacts. Energizing Boost Pump Relay
(BPR)closes normally open BPR contactsto start Boost
Pump Motor (BPM). Energizing Reheat Coolant Valve
opens the valve and starts the flow of engine coolant
through the heating coils. During the heating cycle, this
valve is opened and closed and the pump is started and
stopped on thermostat command to control vehicle
interior temperature.
When the vehicle interior temperature rises to the
setpoint,thethermostat switches fromlow speedheatto
low speed vent mode. In this mode, the thermostat
removes power from plug J1, pin no. 1, which
de-energizes the Reheat Coolant Valve (RCV) and
Boost Pump Relay (BPR) to stop the flow of coolant to
the heating coils. The evaporator fans will continue to
operate on low speed to circulate air throughout the
vehicle.
Figure 2-3. Temperature Controller Sequence
During Heating Mode
FALLING
TEMPERATURE
1˚FABOVE
SETPOINT
SETPOINT SETPOINT
3˚FABOVE
SETPOINT
LOW SPEED VENT
5˚FABOVE
SETPOINT
3˚FABOVE
SETPOINT
1˚FABOVE
SETPOINT
RISING
TEMPERATURE
LOW SPEED HEAT
-2˚FBELOW
SETPOINT

2-4
Figure 2-4. Cooling Cycle---High Speed Vent Mode Operation
Energized Circuit
De-energized Circuit

2-5
Figure 2-5. High Speed Unloaded (2-cylinder operation) Cool Mode Operation
Energized Circuit
De-energized Circuit