Very short version.
Our heat pump is stuck on and the house is overheating.
Very long version.
American Std. Old, 5 ton unit (21 years old)

We Moved here 2 years ago so I no further history with the unit than that

A year ago it quit working…. Am Std. dealer found the thermostat wire was shorted and replaced it.
At the same time the DC controller board for the DC air handler motor partially fried. Visible burnt stuff on the board. (the fan worked correctly until the wire short)

The fan still worked…. but we lost the soft ramp up feature and the fan will not turn completely off. It goes to a minimum speed between cycles, and even if turned off it still idles at that slow speed. Only turning the power off will completely stop it. The tech has double checked the thermostat wiring and says it is correct. We could live with that, and have, for the past year because the tech advised the board was hard to get and would be ~600 bucks! We decided to just ride it out until we had to replace the unit and requested an estimate. He never got back to us with an estimate and it was working so...

Fast forward a year.
AC functioned perfectly the last two summers, It will easily keep the house any temp you desire and only run 1/2 to 2/3 of the time. However, in heat mode the thing has always been flakey. I have had trouble regulating the heat. Sometimes it seems to stop heating… Fan on but blowing cool air. the house gets cool but turning the thermostat off / on or up / down seems to remedy the problem. Sometimes it gets too cold, sometimes it gets a little too warm, like the thermostat was a little lazy. I thought I might need to replace the old thermostat to maybe try fix the inconstant heat problem but…

...today it stuck on heating and had overheating the house by ~10° before I cut it off.
Now, even turning the thermostat to “OFF" doesn’t stop it, and neither does turning it to AC… It keeps running and blowing hot air until I kill the power to the unit at the switch box.

It’s old, and I don’t want to spend a bunch on it but if might be something simple like a flakey / now stuck relay I might attempt to fix it. I think the thermostat isn't just stuck because it's an old mercury tube type and you can see it work.

I’ll attach a couple photos.

Any thoughts would be appreciated before I call the man. I open it up tomorrow and have a look.

This message has been edited. Last edited by: cparktd,

Stuck contactor

It continues to operate with the front of the thermostat off?

If so, go pull the red wire from the air handler (package unit) to see if it stops running.

If it continues to run with the red wire disconnected, the contactor is stuck.

quote:

Originally posted by Excam_Man:
Stuck contactor

It continues to operate with the front of the thermostat off?

If so, go pull the red wire from the air handler (package unit) to see if it stops running.

If it continues to run with the red wire disconnected, the contactor is stuck.

Thank you sir!

Yes, runs with the T'stat front off.

Left it turned off last night, back on and letting the house warm back up now...

I will have a look shortly.

Got lucky and found the damaged board that had it limping along for the last year used on e-bay, looked for it at the suggestion of the local Am-Std. dealer. It's a used one. He said he probably couldn't get a new one, likely obsolete, and $$$$ even if he could.

Also got the main Contactor, and also found the coil was bad on one of the aux heat bank contactors preventing it from working.

She seems to be functioning perfect now. ~$65 in parts total. I'm pretty happy with that.

Just thought you (Excam_Man) deserved an update! Thanks!

The fried board... it worked this way for a year but the air handler did not function correctly. As near as I can tell it works as intended now. Including the variable speed ramp up function.


Fried coil from the larger of the two heat banks.

Thanks for the update, I almost asked how you made out the other day. It's not often that we hear 'the rest of the story'.

Glad you got it running properly. A great start for a new year.

Nice photos!

Your welcome!

Just got it all done, took a few days to get the parts. I still would like a digital thermostat I think...

Just in time. We are expecting 4 or 5 days in a row here with highs in the 20s and lows in the single digits. Pretty cold for us.

Maybe I can relegate the electric blanket back to the closet now!

Thanks for sharing your creative solutions. My system is 17 years old and maybe I will need to fix it like you. ExCam you are a HVAC whisperer.