27KR Electrical Defrost Unit Coolers (PN E108318_S)
3.
The evaporator coil cools down approaching operating temperature.
4.
When the coil temperature reaches 25°F (approximately two to three minutes after defrost
termination), the fan delay thermostat closes thus allowing the fan motors to restart.
The unit is now back in operation.
NOTE: On systems where the room temperature is above +25°F, the fan delay thermostat
may not close for an extended period. If the fan delay time is too long, it is permissible to
install a jumper wire between terminals “F” and “B” at the unit. This allows the fans to turn
on immediately after the defrost period.
9.1
MODELS H - 3 PIPE HOT GAS WITH ELECTRIC PAN HEAT AND P - 2 PIPE
KOOL GAS WITH ELECTRIC PAN HEAT
Three pipe hot gas defrost system - Distribute compressor discharge gas through a separate
hot gas line, controlled by a solenoid valve, through a check valve to the refrigerant distributor
auxiliary side connection. Defrost condensate and gas vapor is evaporated in a re-evaporator
prior to returning to the compressor through the suction line.
Two pipe cool gas defrost system - Distribute compressor discharge gas through the suction
line during defrost. Defrost condensate flows through the refrigerant distributor auxiliary side
connection and a check valve, bypassing the expansion valve and the liquid line solenoid valve
into the liquid line which is reduced in pressure.
The defrost cycle is field controller initiated and terminated.
Step A
Power is supplied to the unit cooler continuously.
Step B
In Case of H, defrost hot gas is supplied to the unit via liquid line and in Case of P, defrost Kool
Gas is supplied to the suction line. A factory mounted thermostat (KP73) senses a rise in the
coil temperature. The SPDT control turns off the fan motors. If the unit has a drain pan heater,
the other portion of the SPDT control is now closed and the drain pan heater is energized.
Step C
When the defrost is complete, the hot gas supply is stopped. The liquid line solenoid is energized,
and the coil temperature begins to fall.
Step D
The factory mounted thermostat senses the drop in coil temperature. The SPDT thermostat
opens the circuit to the drain pan heater (when supplied) and closes the circuit to the fan motors.
Recommended (SPDT) fan delay/drain pan heater thermostat settings:
Room Temperature Range Differential
0°F to +35°F 45°F 15°F
Below 0°F 20°F 10°F
(Note: Fan delay set point = Range – Differential)
A separate SPDT thermostat (KP73) is provided in the coil which can provide a digital defrost termination
input.
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