Heating, Air Conditioning, Fridge, HVAC/heil heat pump rev valve


Pump runs in heat mode only. Replaced t stat w/Honeywell unit. Followed wiring connections. Called Honeywell to double check wiring. 24 v to t stat. compressor runs. Blower fan runs. o/b terminal 24 volts out of t stat. reversing valve terminals only 6 volts. no cooling. does the rev valve need 24 volts? Why do I have such a voltage loss fromi t stat?

I do not know the exact operation of your unit as they are all a bit different between brands and years made.  I will give it my best guess here.

Most cond. units these days have a defrost board in them.  The 24v from the t-stat is wired to the defrost board and is a control signal to tell the defrost board what to do.  The defrost board gets 24v power directly from the transformer.  The rev. valve is controlled by the defrost board and needs 24v to the coil for it to work.  You need to check the defrost board's operation.


Heating, Air Conditioning, Fridge, HVAC

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Craig HVAC Expert


I have been in the HVAC field for the past 18 years. I can help with most HVAC questions. I work on commerical buildings for the most part, and have yet to find anything I could not troubleshoot and repair, when repairable. I work on small 1 ton units to a 2500 ton chiller. Troubleshoot air flow, elect, and control problems. I attend regular classes to keep up with the latest and greatest.


I work on commerical sites, hospitals, gov't buildings. I can troubleshoot just about anything in the HVAC business.

5 years trade school, VFD training classes, Liebert factory training, some York and Trane factory training.

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