Electric Central Heat unit won't turn off.

[1320stang]

I have a Goodman A36-20 heater that heats my house, but I have a tap for my garage. I have a Honeywell 7 day programmable thermostat in the hallway. It won't turn off even if I have the thermostat off or even unwired off the wall.

https://goo.io/nJwYmJ

There are two heating element modules, one is 5kW and the other is 15kW. The 15kW unit is made up from three 5kW strings. My first problem was that the middle string cracked a porcelain insulator and although it didn't burn through, every time the sequencer would call that string up, it would trip the breaker. My solution was to remove the jumper wire off the high limit. Then every time that string was called on to start, I wouldn't have any heat, but all I'd have to do is turn the thermostat off, then on and it would sequence to the next element.

Eventually that no longer worked, so I replaced the 15kW module ($70)and everything seemed fine, but it got cold and I had no heat every so often. Not sure if it ever worked right. I called a guy we do HVAC projects with and he said it was likely the sequencer, so $20 later and I'm good to go.

It all worked fine for a couple days, then the breakers started tripping again. What happened was that one of the female connectors that comes directly from the unit breaker was loose and had vibrated off the terminal on the module. This also had a wire jumpered onto it that lead to the 24v transformer. I figured the timer might be bad so I replaced it ($18)and I also replaced the transformer ($12), even thinking that wasn't it. (It wasn't) I also swapped out a high limit switch on that string with one from the old module.

Now I'm thinking it's either the sequencer of the thermostat, but again, if the thermostat is off, the unit still runs.

I'm going to pull the elements out again to give them another inspection but I'm at a loss. What I've spent so far is cheaper than a service call, but all I'm doing is throwing parts at it.

 

[bazar01]

"I have a Goodman A36-20 heater that heats my house, but I have a tap for my garage. I have a Honeywell 7 day programmable thermostat in the hallway. It won't turn off even if I have the thermostat off or even unwired off the wall."


You have a strange issue but not impossible.

Is the indoor fan running as well as the heat strips with the thermostat off or unwired off the wall?
If yes, then the fan relay and sequencer contacts are welded in closed position. Turn breaker OFF and check normally open contacts for continuity.

Or there is a 24VAC control voltage from transformer feeding the fan and sequencer relays. You will need a meter to check that.

Good luck.

 

[Milton Shaw]

The Tstat wiring could be shorted between the tstat and the unit. Unhook the wires from the unit and see if it turns off then. I have seen a lot of them with nail/screw through the low voltage wiring.

 

[jonathan75]

My blower unit would run randomly when my thermostat never even asked it to. I called the manufacture and spoke to tech support. They said it was simple, just replace the relay. I went down the road and picked up a relay for $20 and never had a problem since. This may not be your problem but it may be worth a shot to call the manufacture. Sometimes you can find someone that knows something any they may be happy to tell you what the common problems are.

 

[EOC_Jason]

Yeah, those old units there aren't too many parts and it's better than newer models with the circuit boards in them.

I would try what Milton said first since that's the easiest. Like he said a nail could be in your low voltage wire, or even a critter might have been gnawing at it.

Then I would try what bazar said.... My first thought too was the sequencer, and even though you said you replaced it they are cheap parts (and cheaply made) so you never know. Sometimes it's just a matter of using a meter and following the wiring diagram to diagnose what part is bad. Just be careful if you are working on that unit with the power on and the panel off.