Service Manual

TECHNICAL SUPPORT MANUAL Split System Heat Pump: (H,C,T)CH(6)
8 428 04 170100
The control board accumulates compressor run time. As the accumulated run time approaches the selected defrost
interval time, the control board monitors the coil temperature sensor for a defrost demand. If a defrost demand exists,
a defrost cycle will be initiated at the end of the selected time interval. A defrost demand exists when the coil temperat-
ure is at or below 32° F(0° C) for 4 minutes during the interval. The defrost cycle is terminated when the coil temperat-
ure reaches 65° F (18.33° C) or 10 minutes has passed. When OAT is >25° F(--3.9° C), defrost will occur in low or
high stage as demanded by the thermostat or Wall Control. If OAT is <25° F(--3.9° C), defrost will occur in high stage
only, regardless of thermostat or Wall Control demand, and will terminate at 50° F(10° C) coil temperature with a min-
imum of 2.5 minutes in defrost. If the coil temperature does not reach 32° F(0° C) within the interval, the interval timer
will be reset and start over. Upon initial power up the first defrost interval is defaulted to 30 minutes. Remaining inter-
vals are at selected times. Defrost is only allowed to occur below 50° F(10° C) outdoor ambient temperature. The out-
door fan output (ODF) will remain off for 20 seconds after termination. This delay will allow time for the system to cap-
ture the heat from the outdoor coil and reduce the “steam cloud” effect that may occur on transition from defrost to
heating cycle.
Defrost
Field initiated forced defrost
On a system with non--communicating (non--Observer) control, forced defrost can be initiated by manually shorting
the 2--pin header labeled FORCED DEFROST (see page 6) on the control board for 5 seconds then releasing. If
coil temperature is at defrost temperature of 32° F(0° C), and outdoor air temperature is below 50° F(10° C), a full
defrost sequence will occur. If coil temperature or outdoor air temperature does not meet the above requirements,
an abbreviated 30 s econd defrost will occur.