OT Heatpump ?

Back in Dec. the coils on the outside unit froze up. 2T Trane only a couple or 3 yrs old. BIL that has some background in HVAC come over and did some troubleshooting. Best we could come up with was that the thermocouple/thermister was bad. I replaced that and have not had anymore freeze ups.
But heres the problem. Double $$ electric bills.
We have a 2 story house and this unit is for the upstairs. This morning when I got up I thought it was a little warm, I felt the air from the register and it was warmer than your usual HP air. Checked thermostat and saw that the aux heat was on. Thermostat is set at 72 and inside temp was 72 but unit was still running.Dropped thermostat to 71 and Aux turned off. Same model Honeywell digital thermostats used upstairs and down.
Outside temp this morning was 38~.
I have also replaced the defrost board (with a used 1) but don't see any change.

Why is the unit using the Aux heat (or what tells it to come on)? At what point is the thermostat satisfied and will cut off the unit?

Thanks if anybody can help.
Oh buy the way I saw it was froze up while pushing snow with the 52 8N. (tractor link) :<))




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First thing is to make sure the heat pump is fully charged and working properly. The Honeywell thermostats can have the aux. heat programed for comfort or economy. In the comfort mode the thermostat will bring on aux. heat if it does not see a temperature rise within a few minutes. In the economy mode the aux. heat will not come on unless room temp drops 3 degrees below tstat setpoint. Most digital t stats will turn off at 1 degree above set point and back on 1 degree below setpoint. You may have a problem with outdoor unit and thermostat is using aux. heat to meet heat demand. DH

my Lennox system does same thing but backwards...heat strips turn off about 4* cooler than heat pump does...electric meter turns into a strobe when them strips are on...i added propane space heaters few years back...figure i save close to $75. a month plus i'm actually warm.

Your auxillary heat will come on when the outdoor unit goes into the defrost mode to maintain the temp inside the house.