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
Be sure air conditioning unit is turned off before
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 the Reheat/Cycle
Switch located on the unit’s control panel on the roof of
the vehicle. When a mode of operation is selected, the
Electronic Thermostat (TH) senses the vehicle’s interior
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.
The unit control circuit operates on 24-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 is calling for cooling,
the air conditioning (cooling) circuit is activated. With
the switch in this position, 24-volts is supplied to the A/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). Applying power to the thermostat allows
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, applying power to thermostat plug J1, pin no. 3;
this energizes the Clutch Relay (CR), Condenser Speed
Relay (CSR) and Condenser Fan Relay (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
