MK/MV – Medium Profile Series Unit Coolers (E206993_M)
29
8
GAS DEFROST SEQUENCE OF OPERATION
The hot gas defrost cycle is time clock initiated and terminated.
8.1
HGE/HGG 3 PIPE HOT GAS DEFROST
Three pipe hot gas defrost systems 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 is evaporated in a liquid-line/suction-line heat exchanger, prior to
returning to the compressor through the suction line.
8.2
SEQUENCE OF OPERATION
1.
Upon initiation of the cycle, the timer contacts “1” and “4” opens thus de-energizing the liquid
solenoid valve and the fan motors. If the unit has electric drain pan heater, contacts “4” and “5”
close, thus energizing the drain pan heater. The compressor pumps the refrigerant out of the coil.
2.
The timer contacts “4” and “2” closes, thus energizing the hot gas solenoid valve and allows hot gas
to flow into the coil through a check valve and the refrigerant distributor auxiliary side connection.
3.
After the timer timeouts contacts “4” and “2” open, thus de-energizing the hot gas solenoid valve.
During this period the coil pressure will vent down to the compressor suction pressure.
4.
Upon termination of the vent down cycle the contacts between “4” and “
1” close, thus de-energizing the drain pan heater if the unit is equipped with one. The contacts
between “4” and “1” close, thus opening the liquid line solenoid valve and starts the fan motors.
Figure 16 (H) HGE - 3 PIPE HOT GAS COIL AND ELECTRIC DRAIN PAN DEFROST WIRING
T
(OPTIONAL)
HEATER
DRAIN PAN
FAN MOTORS
1 THRU 4
SOLENOID
LIQUID
T
1
T
2
L
1
T'STAT
ROOM
HOT GAS
SOLENOID
L
2
GRD
DEFROST TIMER
1
3
2
4
6
5
208/60/1 OR
EARTH GRD
230/60/1
L2
(BY OTHERS)
FUSED DISCONNECT
L1
GRN
