Trane ACONT900AC43UA Service Manual page 49

Communicating Air Conditioning and Heat Pump Systems
Section B
20 SEER Heat Pump Model Control Boards ...................................................................................... 2
Overview ......................................................................................................................................... 2
Sump Heater Control ...................................................................................................................... 2
Sump heater operation at power up ........................................................................................ 2
High Pressure Monitor Logic ............................................................................................................. 3
Low Pressure Monitor Logic .............................................................................................................. 3
Cool Mode LPCO Logic ...................................................................................................................... 4
Low Temp Lockout in Cool Mode ..................................................................................................... 4
Timing Logic for LPCO Open Events ................................................................................................ 4
Sensor and Control Voltage Fault Detection ..................................................................................... 5
Power Interruption Protection ............................................................................................................ 6
Oil Return Mode 20 Seer Heat Pump Models .................................................................................... 6
Ambient Temperature Sensor and Oil Return Mode ........................................................................ 6
Charge Assist Feature All Models ...................................................................................................... 7
Demand Defrost Cycle Heat Pump Models ........................................................................................ 7
Defrost Component Electrical Wiring .............................................................................................. 7
First Defrost Event .......................................................................................................................... 8
Terminate Temps ............................................................................................................................ 8
Diagnostic LED .............................................................................................................................. 8
Demand Defrost Control Checkout .................................................................................................. 9
Board Variations ................................................................................................................................. 9
Control Boards
HP - B 1