[Mary919]

Hi. I'm in North Carolina, so it's been cold here but not cold like in other parts of the country. I mention that because I wouldn't say our heat has had a heavier load than normal.

A few weeks ago we noticed an electrical burning smell in the middle of the night. We turned the heat off, my husband went out and looked around the heat pump and shined a flashlight around the duct work in the cellar-- nothing. We went back to bed. In the morning the house was chilly and since we were up and could monitor it, we turned it back on-- no problems and no trouble since.

This morning it happened again-- we turned the system off and checked everything again. This time we noticed that the vent closest to the heat pump was very hot so that even with the system turned off residual heat was radiating out. It seems like something is overheating.

We haven't manually turned the emergency heat on, but I'm wondering if the system can do that itself and that that's what we're smelling and that there's an element right near that first vent. Could it be something as simple as that? It was colder last week than it was today, so I'm wondering why now?

Thanks for any help!

- Mary

[hvac1000]

This time we noticed that the vent closest to the heat pump was very hot so that even with the system turned off residual heat was radiating out. It seems like something is overheating.

You probably have a bad heat sequencer allowing the electric heaters to come on without the blower and that will create a situation like you are having. I suggest you call for a On Site service since most homeowners cannot repair this type of problem.

[KC13]

Another possibility is a blower motor that is failing. The auxiliary heaters will cycle via the limit controls, but the plenum will get pretty hot. Was the blower running when you observed this? Try this: set thermostat system selector to "off" and fan selector to "on". Does the motor run, or slow down and stop after a few minutes?

[Mary919]

Another possibility is a blower motor that is failing. The auxiliary heaters will cycle via the limit controls, but the plenum will get pretty hot. Was the blower running when you observed this? Try this: set thermostat system selector to "off" and fan selector to "on". Does the motor run, or slow down and stop after a few minutes?

You're right-- Since I posted the fan has stopped running altogether. That plenum heater (just looked that up!) seems stuck on-- the only way we've gotten it to turn off was to unplug the entire system. When we plugged it all back in the same situation remained-- no blower with the heat on/fan auto, heat on/fan on, heat off/fan on, even with the A/C on-- no blower and plenum heater on.

The house (1005 sf) is staying fairly warm-- is it dangerous to leave the plenum heater on with no blower? I'm thinking it might be! We're having it serviced tomorrow. THANKS!

[KC13]

Not only dangerous, but you would be risking further system damage.

[Mary919]

Not only dangerous, but you would be risking further system damage.

Alright-- we've unplugged it and are preparing to get pretty cold!

One last question and again, thank you very much for all your help-- why does the plenum heater stay on when the heat is turned off? Does this have to do with the outside temperature or does it mean we have some other problem there?

[KC13]

The other possibility, as hvac1000 suggested, is a faulty sequencer/heat relay that is not bringing on the blower and not turning off the electric elements. Whatever the case, this is not a candidate for DIY. Good luck and stay warm.

[Mary919]

You probably have a bad heat sequencer allowing the electric heaters to come on without the blower and that will create a situation like you are having. I suggest you call for a On Site service since most homeowners cannot repair this type of problem.

Wow. I completely missed this answer earlier-- and it answers both my concerns. Thank you! We're getting serviced tomorrow.