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Please help, new tech just out of school. Sent on no heat call today, heat pump with air handler. A/C running fine. house tstat said indoor temp was 70, I turned on heat and set at 73. I removed door on air handler and board is flashing once green. this is call for cooling, however tstat is saying heating. I go to outside unit push contactor in and it runs, let go and it stops. I removed power from the reversing valve and reapply and I can hear the reversing valve move. when its on a/c outside unit runs fine, I switched out t stat and still only one green flash call for cooling. white is for heating 2nd stage does this sound like a bad wire? I bump tstat up to 85 and electric heat kicks on . outside unit is still not running. air handler board still has one green light for cooling. Any suggestions.
 

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What brand and model thermostat?

How is the thermostat wired? As in what wires are where.
 

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Check and see if you are getting 24 VAC to the condenser , when the TSTAT is calling for heat ?

If you are getting 24 VAC to the condenser , check each limit / safety device in the contactor coil circuit to see which one of open / " off " .

If you are not getting 24 VAC to the condenser when the Tstat is calling for heat , check it at the the Tstat .

If 24 VAC is present on the heat terminal of the Tstat , I would suspect the wiring and / or splices going to the condenser .

If 24 VAC is not present on the heat terminal of the Tstat , I would suspect the Tstat . Jumper from the Red ( 24 VAC " Hot " ) to the heat terminal of the Tstat & see if that brings on the heat pump ?

God bless
Wyr
 

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The point here is you will get a Y signal for heat or cool, that is the 24v that starts the compressor. If AC is working but not heat we can rule out a lot of the things that were already mentioned (limits etc.)

It sounds like the thermostat is not setup to use as a heat pump system. What type of stat is it? Also what type of equipment is it? Once the compressor is running you will need to know if the reversing valve needs to be energized in cooling ("O") or heating ("B").....this could be menus or different terminals depending on the stat.

-Jason
SUREFIRE Mechanical- Long Island Air Conditioning Repair Experts
 
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