United Technologies Carrier TRANSICOLD 68RM35-604-20 Operation And Service page 19

(BPR), Water Pump Relay (WPR) and Reheat
Coolant Valve (RCV) stopping the flow of engine
coolant through the heater coil. The system is now
operating in semi-unloaded COOL mode with low
speed evaporator fan operation.
When the vehicle's interior temperature rises to
3 _ F above the thermostat set point, the
(1.7_C)
HEAT/COOL switch remains in the COOL position
but the HIGH/LOW switch switches to HIGH. The
signal from the thermostat continues to keep the
compressor in semi-unloaded (4-cylinder)
operation. The system is now operating in
semi-unloaded COOL mode with high speed
evaporator fan operation.
When the vehicle interior temperature rises to 5
above the thermostat set point, the
(2.8 _C)
HEAT/COOL switch remains in COOL and the
HIGH/LOW switch remains in the HIGH position.
The thermostat discontinues supplying the signal
to semi-unload the compressor and the
compressor becomes fully loaded. The system
now operates in the fully loaded (6-cylinder)
COOL mode with high speed fan operation.
T-288
3˚F ABOVE
SETPOINT
1˚F ABOVE
SETPOINT
SETPOINT
F
_
2˚F BELOW
SETPOINT
5˚F BELOW
SETPOINT
45˚F
AMBIENT
FALLING
TEMPERATURE
Figure 2-1. Thermostat Control Sequence
Auto Cool Mode with Reheat
2-2
RISING
TEMPERATURE
HIGH SPEED,
5˚F ABOVE
FULLY LOADED
SETPOINT
(6-CYL) COOL
HIGH SPEED,
3˚F ABOVE
SEMI-UNLOADED
SETPOINT
(4-CYL) COOL
LOW SPEED,
SEMI-UNLOADED
(4-CYL) COOL
LOW SPEED,
SEMI-UNLOADED
(4-CYL) COOL WITH
REHEAT
3˚F BELOW
SETPOINT
HIGH SPEED,
SEMI-UNLOADED
(4-CYL) COOL WITH
REHEAT
HIGH SPEED,
COMPRESSOR OFF
FULL HEAT
SETPOINT
55˚F
AMBIENT