Charge Assist Feature All Models; Demand Defrost Cycle Heat Pump Models; Defrost Component Electrical Wiring - Trane ACONT900AC43UA Service Manual

•
Ambient Sensor fault (open) = Oil Return Mode
exits allowing Defrost Control to assume low tem-
perature below 6' F (Defrost every 3 hours)
•
Ambient Sensor fault (shorted) = Oil Return Mode
exits (Defrost does not function - same as today)
Err 67 on Comfort Control
5 flash from OD control Fault LED
•
Ambient Temperature sensor out of range:
Too low = possible unnecessary Oil
Return Mode initiation
Too high = possible failure to initiate Oil
Return Mode when required
•
Coil Sensor out of range:
Too low = Defrost cycle times out
(15 minutes max)
Too high = Defrost cycle exits prematurely

Charge Assist Feature All Models

The Integrated Control Board features advanced charg-
ing capability called Charge Assist. Refer to the Charge
Assist section of this book for details.

Demand Defrost Cycle Heat Pump Models

The defrost control board is a demand type defrost
control. The Integrated Control Board monitors the
outdoor air temperature and the outdoor coil tempera-
ture and initiates a defrost cycle upon demand.
During a defrost cycle the switchover valve is ener-
gized to cooling mode position, the compressor runs,
the outdoor fan motor is off and back up heat is ener-
gized. The system will run in defrost mode until either
the termination temperature or time over ride is reached.
When defrost terminates, the control board will initiate
a soft-switchover routine to minimize noise from the
refrigeration circuit.
Control Boards

Defrost Component Electrical Wiring

The Coil Sensor (see Figure 13) is a negative coeffi-
cient thermister that changes electrical resistance with
changes in outdoor coil temperature. The thermister
is mounted onto the outdoor coil and connects to the
control board on Plug J6.
Figure 13
The Ambient Temperature Sensor (see Figure 12) is
also a negative coefficient thermister that hangs near
the outdoor coil to sense the temperature of the out-
door air. The sensor is mounted to the control board
on Plug J7
Service Facts shipped with the outdoor unit contains
a table (see below) of resistance values versus sensor
temperatures.
HP - B 7