HVAC experts - Help!

[Masked Bandit]

So I have a gremlin in my furnace. He's shown up twice now in the past two years we've lived in our brand new house. Both times after running the furnace fan "on" for a couple of days (once in summer and once in the winter) the fan refused to turn off. After I had switched the thermostat to "off" for the fan, it would keep running. After an additional 24 hours of this I shut the switch off to the entire furnace and of course it stopped however as soon as I turned the furnace switch back on, the fan fired up again. Eventually after about another 24 hours it just stopped and resumed normal operation.

Now when this happened last summer I called the company that installed the furnace & air conditioner in the house (Central Aire) and they sent someone out. The problem was that he couldn't recreate the problem so he couldn't really find anything. He checked this and that but said to just call again if it happens. That call was free, but this time it's two years later and I don't think it would be. However again like last summer after a couple of days it just went back to normal.

Both times the furnace would function as usual if the thermostat would call for heat or AC but after it was done running it's cycle it would drop back to the fan running (at half speed, it's a dual stage motor).

What the hell?

[Supa Dexta]

I know nothing..

But... sounds like a relay sticking or something..

[JfuckinC]

Sounds like a stupid question, but do you have a light switch up stairs controlling it? When we moved into our house it took us a good fucking 6 months to figure out we did :rofl:

[Masked Bandit]

Originally posted by JfuckinC
Sounds like a stupid question, but do you have a light switch up stairs controlling it? When we moved into our house it took us a good fucking 6 months to figure out we did :rofl:

lol...nope, nothing like that. We also have a vent fan that will basically serve the same function but that has been crossed off the list.

[benyl]

When you turn on the ventilation switch, it turns on the bathroom fans to exhaust the air out of the house.

If you go upstairs and turn on the bathroom fan while the ventilation fan is on, it will stay on even when you turn off the ventilation fan down stairs.

Could that be the issue?

[JfuckinC]

Yah we have two switches, one controls the upstairs fan and another for the Furnace fan.. Sorry i couldn't help haha

[Masked Bandit]

Originally posted by benyl
When you turn on the ventilation switch, it turns on the bathroom fans to exhaust the air out of the house.

If you go upstairs and turn on the bathroom fan while the ventilation fan is on, it will stay on even when you turn off the ventilation fan down stairs.

Could that be the issue?


Nope, that can't be it. Our bathroom fans are some kind of crazy loud and they don't get turned on for any more than a couple minutes. If one was on (even in the basement) I would know.

[alloroc]

In our house there is a current sensor on some of the house electrical.

If any large amp draw items are running (120v) (microwave vacuume etc. the fan comes on.

[Ca_Silvia13]

Do you live in a new house?

What im getting at is in High Efficency furnances they have variable speed motors. They run 99% of the time at varing speeds. Its normal.

[Masked Bandit]

Originally posted by Ca_Silvia13
Do you live in a new house?

What im getting at is in High Efficency furnances they have variable speed motors. They run 99% of the time at varing speeds. Its normal.

The house was built new in 2008 but the furnace fan absolutely should not be running (at low speed or any speed) continuosly.

[captain134]

There is really only two things that would cause this IMO.

If the motor is not variable speed then there must be a contactor that starts the motor. Most likely the points are bad and its staying engaged. Also it could be the Furnace controller itself that is faulty and maybe it is sending Voltage to the contactor to keep it running when it shouldn't be.

Could you post the model of your Furnace please?

[Ca_Silvia13]

Originally posted by Masked Bandit


The house was built new in 2008 but the furnace fan absolutely should not be running (at low speed or any speed) continuosly.

I really think that your confused between the operation of an old low-mid effiecncy furnance and a high effiency. My high effiency furnace at home only turns off for 2mins to heat the heat exchanger then the fan fires right back up. Otherwise it constantly blows unheated air through the ducts ie. constantly running the fan.

I hope this helps, posting the furnace model will definitely help determine if it is in fact a high effiency furnace or not.

[Darell_n]

Originally posted by captain134

Could you post the model of your Furnace please?

And thermostat.

[Iqoair]

Originally posted by Masked Bandit
So I have a gremlin in my furnace. He's shown up twice now in the past two years we've lived in our brand new house. Both times after running the furnace fan "on" for a couple of days (once in summer and once in the winter) the fan refused to turn off. After I had switched the thermostat to "off" for the fan, it would keep running. After an additional 24 hours of this I shut the switch off to the entire furnace and of course it stopped however as soon as I turned the furnace switch back on, the fan fired up again. Eventually after about another 24 hours it just stopped and resumed normal operation.

Now when this happened last summer I called the company that installed the furnace & air conditioner in the house (Central Aire) and they sent someone out. The problem was that he couldn't recreate the problem so he couldn't really find anything. He checked this and that but said to just call again if it happens. That call was free, but this time it's two years later and I don't think it would be. However again like last summer after a couple of days it just went back to normal.

Both times the furnace would function as usual if the thermostat would call for heat or AC but after it was done running it's cycle it would drop back to the fan running (at half speed, it's a dual stage motor).

What the hell?


We had the same problem with ours, it ended up being a relay.

[Masked Bandit]

Well after a bit more research I don't know what the hell to think.

It turns out that the unit is a Lennox G51 which is in fact NOT a dual stage set up. I remember distinctly asking for a dual stage furnace so now I have to find my papers from the build and see what I actually paid Cardel for.

From what I can find, this particular model is supposed to have a continuos low-speed operation function available. This implies that you can either have that function on or off. Well I would have no idea how to activate or deactivate that so what are the chances I could do it BY ACCIDENT twice in two years from the thermostat? Highly unlikely. And if that is the case, why the hell didn't the service tech from Central Aire offer that as a possible cause?