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Heating, Air Conditioning, Fridge, HVAC/Aux heat (coils) always energized

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First let me say that I have no formal education on HVAC systems.  I attempt to self-educate on specific issues and probably know just enough to be dangerous (if that).  I have a Nordyne heat pump (Q5RD series) that's at least 10 years old.  The contactor that mounts onto the heat strip assembly died (burned out?), stunk up the place, and would no longer energize the heat strip when called for.  The coil on the back of the contactor was covered with rust, so I assume excess moisture may have caused this and ultimately caused it to fry.  I replaced the contactor and now the heat strip is constantly being supplied with power, even when the thermostat is off.  The only way to stop it is to kill the breaker to the unit.  Otherwise, everything else seems to be operating fine.  Unfortunately, I can't disconnect the power wires to the heat strip because the blower then will not run.  After talking to HVAC acquaintance over the phone about this, he told me it's probably the sequencer on the heat strip, so I replaced it but that didn't change anything.  He then said perhaps the control board had gone bad (he questioned why the contactor went bad in the first place and suggested a power surge that could have damaged other electrical parts. My unit is apparently so old that there is no fuse on the board so I'd have to buy a new board just to eliminate that possibility).  To me, this seems to be something simple that would require me replacing another part, but I don't want to go through the process of elimination and spend a lot of money I don't have with no guarantee that it will be fixed.  I'd appreciate any info you can provide.  Please let me know if you have any additional questions.

Thanks!

Answer
Based on what I read, it is not clear to me what the exact issue is.

Is the contactor coil energized for the heat strips?  If the coil is energized, then removing one wire from the coil  will stop the heat strips from coming on.  There is no need to disconnect the line voltage wires.  

Changing parts is not the way to figure out what the problem is.  You need a meter and know out to use it to determine what is causing the problem.

Craig
achelpguy@gmail.com  

Heating, Air Conditioning, Fridge, HVAC

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Craig HVAC Expert

Expertise

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.

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

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

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