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heat pump won't run

I am dealing with a 2 ton Advanced Air heat pump. The outdoor unit will not run. It is getting high and low voltage. I pressed the contactor and the fan started. The led troubleshooting codes are telling me that everything is fine. The compressor does not hum. I am thinking that it is in the control board. I'm not sure if i'm right though. The indoor unit does run properly.


  • Coany
    Coany Member Posts: 91
    low or high pressure switch?

    blocked air filter will trip high pressure switch in the heating mode.

     you say its getting 24v but is it calling,, is there a pan switch, or an overflow switch on the condensate pump.

     look for any manual reset type switch on any pipe inside the condensing unit.
    " Do what you can, with what you have, where you are" Teddy Roosevelt
  • john0970
    john0970 Member Posts: 4

    there is no condensate pump....condensate is piped directly outside. The l.e.d lights on the outdoor unit do not show a high or low pressure problem.
  • Coany
    Coany Member Posts: 91
    edited January 2010
    check to be certain it is calling for heat

    by what your saying I'd be looking hard at that,

     make sure its not in the emergency heat mode

     does the board have an indicator  that it is indeed calling for heat
    " Do what you can, with what you have, where you are" Teddy Roosevelt
  • john0970
    john0970 Member Posts: 4
    no emergency heat

    unit does not have emergency heat. unit is 3 years old and the indoor unit comes on when it calls for heat.
  • sasman
    sasman Member Posts: 29
    h-p won't run

    just how far are you getting 24v?
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    Sounds like...

    If you have both line voltage and low voltage at the outdoor unit, it sounds like you have either an open pressure switch or a defective contactor coil.

    You mentioned that the outdoor fan operated when you manually pushed in the armature on the contactor, so your line voltage power circuit seems to be intact.

    You should take a voltage reading across the contactor coil on a call for heat and determine if you indeed have 24 volts at the coil. If you have low voltage at the coil, the coil is defective and the contactor needs to be replaced.

    If there is not voltage across the coil, it is likely that there is an open pressure switch. On many heat pump systems, the pressure switch is the only safety/operational device in series with the contactor coil at the outdoor unit. The common side of the coil often retrns to the indoor unit via a common terminal connection on the defrist control.

    Keep us posted.
  • john0970
    john0970 Member Posts: 4
    new contactor and reset low pressure

    i installed a new contactor and reset the low pressure switch. maybe it's not getting a call for heat. i checked all the low voltage connections in the indoor unit. maybe it's the t-stat?  this is driving me
  • Techman
    Techman Member Posts: 2,144
    Heat Pump

    What mfg makes this H.P.?At the outdoor unit ,with the system  calling 4 heat,do u have 24v on the common and heating{hot} wire? Is the 24v side of the xformer grounded?If yes, put 1 probe 2 ground and the other probe to the heating [hot] wire .You should have 24v.Then hopscotch thru the switches to the hot side of the contactor.Do u have 24v all the way?If yes, put the 2nd probe on the common side of the contactor,do u have 24v there?If yes then ur common leg is open somewhere, or both 24v legs are the same leg.
  • Empire_2
    Empire_2 Member Posts: 2,343

    Can you provide a wiring diagram?  I'm sure one of us can help you through it.  From what you are telling us, one of the safeties must be open.  Step back for a while and trouble shoot from the contactor back if you can.

    Mike T.
  • JStar
    JStar Member Posts: 2,752
    Have you...

    ....ohmed out the compressor to make sure it's still working? Does it work in cooling mode? 
This discussion has been closed.