Trane 1100 heat pump

[BigAlf]

I have two Trane heat pumps. The older one has suddenly been going to 'auxillary heat' when heat is called for and switches to 'heat' once temps are reached. The fan is running and the gas side tubing is hot. The thermostat settings are only 2-3 degrees steps. Anyone with ideas, I will appreciate it.

[nomadpeo]

how's the weather * colder than normal *

does the unit only leave aux at the end of the cycle or does it continue to heat *

[BigAlf]

Testing post

[BigAlf]

The weather is warmer last few days than two previous weeks. Unit worked well during tht cold spell. I think. I just noticed a day or so ago when first thing in the morning the temp for that part of house was 6 deg below set. 'Aux heat ' stays on until nearly meeting setpoint then switches to 'heat'.

[nomadpeo]

if the unit is runs aux in two instances : the heat pump can't keep up and the heat strips are being used as 2nd stage heat, or aux heat is being called for by the defrost relay sending a signal from the outdoor unit. the latter happens when the system goes into defrost. does not sound like it is in defrost because the line is hot. it's normal for the hot gas to be routed to the indoor coil during normal heat pump operation. if aux is showing up at the beginning of the cycle, this could indicate a false signal from outsid, possibly a defective defrost board. verify operation outside at the beginning of the heat cycle (cold air discharging) and check aux signal from defrost relay. should not be present.