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2.1
STARTING AND STOPPING INSTRUCTIONS
a. Starting
1. Start the vehicle engine.
2. Place the ACMS switch in the AUTO posi-
tion.
NOTE
The engine coolant must be warm enough
to close the engine coolant switch (if
installed) for unit operation to start.
b. Stopping
1. Place the ACMS switch in the OFF posi-
tion.
NOTE
Be sure air conditioning unit is turned off
before stopping the vehicle 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
When the ACMS switch is put in the AUTO
position, the control thermostat senses the
vehicle's interior temperature and automatically
controls the system to maintain the desired
temperature set point.
The unit control circuits and components operate
on 24-volt power supplied by the bus battery or
alternator.
2.3.1 Air Conditioning Auto/Reheat Mode of
Operation (See NO TAG.)
To operate in the Auto mode of operation, place
the ACMS switch in the AUTO position. The
thermostat will then determine at which points
cooling or heating are required to regulate vehicle
interior temperature.
With the ACMS switch in the AUTO position, 24
vdc is supplied to Evaporator Fan Relays (EFR1
and EFR2) and Electronic Thermostat (TH).
SECTION 2
OPERATION
During Auto/Reheat mode of operation, the
compressor
operation is only stopped when the outside
ambient temperature falls to 45
Ambient Thermostat (LATH) senses ambient
temperature outside the bus and opens a set of
contacts to interrupt the compressor clutch circuit
when the ambient temperature falls to 45
(7.2
_
C). Heat is then accomplished by cycling
Boost Pump Motor (BPM) and Reheat Coolant
Valve (RCV) to supply engine coolant to the heater
coil.
When the vehicle interior temperature falls to 3
(1.7
C) above the electronic thermostat setpoint,
_
the HEAT/COOL switch remains in the COOL
position. The HIGH/LOW switch remains in the
HIGH position. A signal from the thermostat
unloads the compressor down to semi-unloaded
(4-cylinder) operation. The system is now
operating in the COOL mode with high speed
evaporator fans and semi-unloaded compressor.
When the vehicle interior temperature falls to 1
(0.56_C) above the thermostat set point, the unit
remains in the COOL mode but the HIGH/LOW
switch switches to LOW position. The signal from
the thermostat continues to keep the compressor
in semi-unloaded (4-cylinder) operation. The
system is now operating in the semi-unloaded
COOL mode with low speed evaporator fan
operation.
When the vehicle interior temperature falls to 2
(1.12_C) below the thermostat set point, the
HEAT/COOL switch switches to the HEAT
position, which energizes Boost Pump Relay
(BPR), Water Pump Relay (WPR) and Reheat
Coolant Valve (RCV). The signal from the
thermostat continues to keep the compressor in
semi-unloaded (4-cylinder) operation.
system is now operating in the semi-unloaded
HEAT mode with low speed evaporator fan
operation and engine coolant flowing through the
heater coil to maintain temperature inside the bus.
When the vehicle interior temperature rises to the
thermostat set point, the HEAT/COOL switch
switches to the COOL position and the HIGH/LOW
switch remains in LOW. The signal from the
thermostat continues to keep the compressor in
semi-unloaded (4-cylinder) operation. Switching
to COOL, de-energizes the Boost Pump Relay
2-1
runs
continuously.
F (7.2C). The Low
_
Compressor
F
_
F
_
F
_
F
_
The
T-288
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