Unit Description (Rev 1/99)
9
Heat (Optional)
The thermostat shifts the unit to heat at temperatures more
than 3 F (1.7 C) below the thermostat setpoint. The thermo-
stat keeps the unit running in heat until the temperature rises
to 2.4 F (1.3 C) above the thermostat setpoint. During
engine operation, the water pump and the evaporator fans
operate while the unit is in heat.
During electric operation, the evaporator heaters and the
evaporator fans operate while the unit is in heat.
Defrost
The defrost cycle can be initiated any time the evaporator
coil temperature is below 42 F (5.6 C). Defrost is initiated
automatically by the defrost timer, or manually by pressing
the Manual Defrost switch.
Initiating defrost energizes the defrost relay. This energizes
the hot gas solenoid to route hot gas to the evaporator, and
de-energizes the fan relay to stop the evaporator and con-
denser fans.
The unit runs in defrost until the evaporator coil tempera-
ture rises to 52 F (11.1 C), causing the defrost termination
switch to open. This de-energizes the defrost relay and ter-
minates defrost. If the defrost termination switch does not
open in less than 45 minutes, the defrost timer will termi-
nate the defrost cycle 45 minutes after is was started.
(1) Shifts from Null to Cool if not previously in Heat
(2) Shifts from Null to Heat if not previously in Cool
Thermostat Algorithm
UNIT FEATURES
• Digital Thermometer
• Electronic Thermostat
• Defrost Timer
• Hot Gas Defrost
• Defrost Termination Switch
• Liquid Injection System
0Setpoint
1 Temperature Drop
2 Temperature Rise
3Cool
4Null
5 Heat (Optional)
AGA329
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