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At a loss with a Bryant Heat Pump

Customer called outdoor unit not running only using E heat.  When the Thermostat calls for heat the display gets a weird and looks like it was just reset.  ( all the icons on the display show at once.)  then it looks normal and gos into E heat.  Sounded like a bad thermostat.  Replaced the thermostat and now I am not getting 24v out of the thermostat on the yellow wire.  Getting 3-17v.  Thought I might have a bad wire so I used on of the other wires there.  Whom ever installed the unit used 10 pair wire.  Tested the wire again and still only 3-17v.  Tested the transformer.  I am getting 28v.  Connected the wire I was using for the yellow to the red 24v.  Got 24v at the thermostat.  Re wired the stat and now nothing on the yellow again.  I measured where the wires enter the indoor unit and out at the outside unit.  Same readings.  There is no place for the voltage to go is there?  It comes out of the indoor unit on red to the thermostat.  Then out on the yellow to the outdoor unit.  The indoor unit is not even tied into the yellow.  


  • drhvac
    drhvac Member Posts: 190
    are you reading

    the 17 volts on the contactor relay? If so, take wires off, and see if you get the right voltage. If so, the relay coil may be bad, what they call shunted.
  • Mac_R
    Mac_R Member Posts: 117

    The low voltage wires go into the defrost board then to the contactor.  I pulled the wire harness off of the defrost board and tested yellow to blue (compressor to common.)  and I only get 3-17V.  I ran a new peace of thermostat wire to the outdoor unit and still no change.  Aruge.  
  • John Mills_5
    John Mills_5 Member Posts: 935

    seen some issues with the defrost boards having internal shorts causing a big voltage drop. Might take Y off the defrost board and straight to the contactor and see what happens. Or leave it unwired, call for compressor and see if you get 24v.

    I had one couple years ago where I thought the short was in the defrost board and it turned out to be 1 wire to the defrost thermostat nicked shorting a bit.
  • furnacefigher15
    furnacefigher15 Member Posts: 514
    Weak Transformer

    You read 24V with nothing loading the transformer, but once there is load, the voltage drops.

    Sometimes this happens when there is a short that was not bad enough to blow it completely.

    I would replace the control transformer as a test and see if the problem goes away.
  • Ironman
    Ironman Member Posts: 7,085

    What gauge wire is it? You said 10 pair; that sounds like phone wire which is 22 gauge.

    The wire should be 18 gauge T'stat cable.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
This discussion has been closed.