I have a new Trane S9X2 furnace I purchased this winter. I want to make sure that everything is setup correctly now in the cooling season. I noticed that the furnace displays "HP1" when the AC is running. According to the manual, this is "Stage 1 Heat Pump" mode. As far as I know, my AC unit does not function as a heat pump. I expected it to display "CL1" for First Stage Cooling.

The AC appears to be working fine. Cold air is being blown out the vents so I'm reluctant to call the service company to take a look.

Is this even an issue? Or is there some minor wiring issue with my thermostat? I have an EcoBee thermostat if that helps.


  • 1
    Is this display somewhere on the furnace? Or is this on the thermostat? Jun 2, 2020 at 21:44
  • There is a small display on the furnace that shows the current cycles its running.
    – joerter
    Jun 3, 2020 at 3:10
  • Did you replace the air conditioner at the same time? Or just the furnace/air handler? Jun 3, 2020 at 3:10
  • I did not replace the air conditioner at the same time. Only the furnace.
    – joerter
    Jun 3, 2020 at 16:50
  • It is quite possible that the control board of the furnace simply triggers different things, including the air conditioner compressor, based on inputs from the thermostat. It is quite possible that the furnace control board could be wired up for any of: Heat Pump, Compressor, Fan Only, when the thermostat calls for "Cool", and the installer simply wired it up for "Heat Pump" - the difference (as far as the furnace) is likely just "which relay gets closed". Jun 3, 2020 at 17:43

1 Answer 1


The outside unit is a compressor , the difference between a heat pump in heating and cooling is the Direction of the refrigerant flow. So for a single fuel heat pump to cool it may well be running in stage 1 but a reversing valve has altered the flow. If you have a dual fuel system then in heating a choice is made based on the temp which one to run. Your thermostat probably doesn’t have all the functionality or was not fully programmed but to get cooling the outside unit needs to run and the reversing valves are set to cool. If it’s cooling everything is fine the thermostat is commanding the compressor on and it has the reversing valve in the correct position.

  • Thanks, so you are saying then that I'm likely good to go and don't have any issues?
    – joerter
    Jun 4, 2020 at 1:26
  • Yes when you select cooler temps and it cools correctly it is correct the heat pump is pumping cold inside and hot outside.
    – Ed Beal
    Feb 28, 2021 at 18:58

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