Heat pump switches to heat mode randomly..

[roy25101]

Got a call from my wife. She said AC was blowing hot air. I assumed she meant non cold ambient air. Turns out it was actually heated air.

Tech was called by her and he also assumed it was non cold ambient air. He troubleshoots system and can't find anything definitive. He mentions the age, R22, a "sticking reversing valve", and that the system should be replaced.

I come home, pull the cover, test the voltage output to the reversing valve solenoid and it is constant.

Later that day the AC randomly switches to heat. I test the output to the solenoid and it is still constant. I shut the system down and cycle the solenoid a few dozen time, no problems.

I open the unit up and find that plug to the solenoid is sitting on the terminal making minimal contact. I plug it back in and all seems well now.

But.. folks on another site seem convinced perhaps the problem will re-arise due to a "simple problem" that they will give no indication of what it is.

Any ideas?

Low voltage to the coil?

Thanks for any input….

[hyperion]

Many of the heat pump systems energise the reversing valve for cooling. Therefore if you have an intermittent connection, the valve would then revert back to the heating mode.
Now that you have put the plug back in place, there should not be any problems until it vibrates loose again.

[install monkey]

had a daikin unit doin a server room- energise for cooling- occasionally going into heating- i diagnosed the solonoid coil being weak as fitting a coil lifter it ran ok for 3 days till new coil arrived- the maintenance eng (sparky thats been there and done that) wouldnt sign my worksheet as he said" theres no such thing as a weak coil- its either faulty or ok", tried telling him that due to the age of coil and breakdown of the insulation around the coil- fell on deaf ears- threw me sheet at him- lasted another 3 yrs till comp died