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D-Compressor Controls
1- High Pressure Switches (S4, S7)
Compressor circuits are protected by a high pressure
switch which cuts out at 640 psig +
10 psig (4413 kPa
+
70 kPa).
2- Freezestats (S49, S50)
Switches de-energize compressors when indoor coil
temperature falls below 29F (-2C) to prevent coil
freeze-up. Switches reset when indoor coil
temperature reaches 58F (15C).
3- Crankcase Heater (HR1, HR2)
Compressors have belly band compressor oil heaters
which must be on 24 hours before running
compressors. Energize by setting thermostat so that
there is no cooling demand, to prevent compressor
from cycling, and apply power to unit.
4- Defrost Switches (S6, S9)
Defrost switches close to initiate defrost when liquid
line temperature falls to 35F (1.7C). The defrost
switch is located on the liquid line between the
outdoor expansion valve and the distributor
5- Defrost Termination Switches (S46, S104)
Defrost pressure switches open to terminate defrost
when vapor (discharge pressure during cooling and
defrost) pressure reaches 450 psig (3103 kPa).
6- Defrost Controls (CMC1)
Defrost is liquid line temperature initiated and
operates for 14 minutes unless terminated by vapor
line pressure drop.
When the liquid line temperature drops below 35°F,
the defrost switch closes and signals the defrost
control that a defrost cycle is needed. If the defrost
switch is still closed after 60 minutes (default), a
defrost cycle begins and operates for 14 minutes.
The defrost pressure switch can terminate the defrost
cycle before the 14 minutes elapses if vapor pressure
reaches 450 +
10 psi.
Electric heat is energized during defrost to maintain
discharge air temperature.
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