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TrilliumLady 12-16-2010 09:06 AM

Is it my furnace or my thermostat? Blows cold and can't shut it off
Furnace is a GrandAire combo with AC. Thermostat is a Hunter weekday/weekend programmable digital thermostat installed last year. FWIW, I rent this house.

Started 3 days ago. Furnace was blowing nothing but cold air and I couldn't shut it (the furnace fan) off at the thermostat. I reset the thermostat. I put it on A/C -- I did everything that I could thing of. The only way that I could stop the fan from blowing was to trip the breaker. Called landlord who called the HVAC folks. They came out and reset the roll-out switch (at least I think that's the correct switch). Ran properly for about 30 minutes. Called back, they came back out and said the switch was bad -- so they bypassed it and would replace the switch the next day. Which they did.

Went out about 1; came home and it was blowing cold air again. Called them back, they came back out (they're very responsive!) and took the cover off. The man said that they blew out the evaporator coil and that should take care of things.

Now, I'm not an HVAC genius (but my husband has more than a passing familiarity -- his dad is RSCS and used to do this for a living, but they're 400 miles away), but ????? Evaporator coil? For heat? From a Furnace?

It's a "self-igniter" (I'm not certain what the proper term is) -- it's my understanding that the thermostat triggers the flow of propane, which causes the igniter to light setting the whole process in motion. Maybe the thermostat triggers the igniter which causes gas to flow. The igniter is lighting properly, something is either shutting it down or stopping the flow of gas. The landlord says that something is cutting the gas off stopping the burners. He says it's around 5 years old -- but I'm not so sure about that.

I can't shake the "feeling" that the thermostat is somehow involved. Why couldn't I make the fan stop at the thermostat even when in the off position?

I'm just not enamored of confidence with these guys -- 4 trips in 2 days. Searching for a Second Opinion from the Collective Mind here!


SKIP4661 12-16-2010 10:25 AM

The roll switch is doing it's job. I suspect the heat exchanger is bad, probably a crack or a popped crimp ring. Bypassing the roll switch puts you and your family at risk for carbon monoxide poisoning. Maybe you should find your own service tech, landlords don't always use the sharpest tool in the shed and hire who is cheapest. Anyone who would run a furnace with the safeties bypassed needs to have their license revoked. The thermostat is not the problem, may need a new furnace. Buy yourself a co detector for your own protection.:eek::furious:

TrilliumLady 12-16-2010 10:45 AM

They did replace the roll-out switch. He bypassed it because it was after 5 and getting dark. They were here about 9AM the next morning. I will, however, get a CO detector.

I kinda trust the landlord -- he owns this house (and he's my boss). But yeah, if the problem keeps up, I just might get a second opinion from somebody else here in town. This is a real rural area, so there's not a lot of options.


Marty S. 12-16-2010 05:09 PM

Sure it wasn't a limit switch? A dirty coil will overheat the furnace from lack of air flow and cause the limit to trip, which leaves the blower on.
On a side note safeties should NEVER be bypassed and left that way, not even for one hour let alone over night.

TrilliumLady 12-16-2010 06:36 PM

those were the two switches that he talked about -- and I wasn't smart enough to write them down.

the switch was on a U-shaped bracket. There was a brown "washer" with a vertical "rod" that was the switch. From the side it kinda looked like a curly brace.

I'll keep that in mind about the safety switches. Thanks!

Marty S. 12-16-2010 06:40 PM

That's a limit switch. A dirty coil could have been the cause. Make sure to change the filter monthly so it doesn't get that way again.

TrilliumLady 12-16-2010 06:51 PM

Thanks. My thermostat reminds me every 400 hours to change the filters. Besides, the Father-in-law would hurt me if I didn't change them!

I have no clue about the previous tennant!

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