SYSTEM OPERATION
20
DEFROST CYCLE
The defrosting of the outdoor coil is jointly controlled by the
defrost control board and the defrost thermostat.
Solid State Defrost Control
During operation the power to the circuit board is controlled
by a temperature sensor, which is clamped to a feeder tube
entering the outdoor coil. Defrost timing periods of 30, 60, or
90 minutes may be selected by connecting the circuit board
jumper to 30, 60, or 90 respectively. Accumulation of time for
the timing period selected starts when the sensor closes
(approximately 31° F), and when the room thermostat calls
for heat. At the end of the timing period, the unit’s defrost
cycle will be initiated provided the sensor remains closed.
When the sensor opens (approximately 75° F), the defrost
cycle is terminated and the timing period is reset. If the
defrost cycle is not terminated due to the sensor tempera-
ture, a ten minute override interrupts the unit’s defrost period.
C
Y
W2
R
R DFT
TEST
DF1
DF2
JUMPER WIRE
90
60
30
A
HEATING CYCLE
The ASZ and SSZ model heat pumps use a different control
circuit than preceding heat pump models. These models do
not use a reversing relay to energize the reversing valve. Also,
many previous models energized the reversing valve off the
"B" terminal on the thermostat, and all previous models
energized the reversing valve in the heating cycle.
The reversing valve on the SSZ and ASZ models is energized
in the cooling cycle through the "O" terminal on the room
thermostat.
These models have a 24 volt reversing valve coil. When the
thermostat selector switch is set in the cooling position, the
"O" terminal on the thermostat is energized all the time.
Care must be taken when selecting a room thermostat. Refer
to the installation instructions shipped with the product for
approved thermostats.