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wavelength 10-08-2009 08:18 PM

blower won't turn on when heat is on, but will turn on when AC is on
I recognize I'm an idiot. I should have left the repairs to a professional. But, we have a two week old baby, and I was rear ended this morning, and my son threw up, and now we don't have heat and I'm about to go eat a banana peel.

SO. I have an April Aire model 600. Which is broken. I opened up my HVAC unit, and noticed the transformer was corroded. Bad. So I drove to some dark corner of the big city and found a place that would sell me a new transformer that goes with the April Aire 600.

After I replaced it, nothing happened. Big deal, I just found out it's under warranty and will be fixed tomorrow.

BUT, when I put stuff back together, I must have missed something. Not only do I now have a pain in my neck and arm, but the blower won't turn on when the heat is on. It's cold outside, and i don't feel comfortable going without heat. The blower turns on when it's on AC.

I'm wondering, did I rewire something wrong? There aren't a lot of options to plug back into. What information do I need to ask an intelligent question to fix this myself? I don't have the cash right now to fork over to a repair person. I will next week, but I can't go without heat that long.

If someone can provide me a web link to a user manual or repair guide that points out the electrical wiring and how the small motherboard on the system needs to bet set up to properly initiate the blower, that'd be fantastic.

Here is the info on the model that I know:

model number: GMP125-5
serial: 9604920844

just wondering where to start to figure out why the blower doesn't kick off during the heating. When I turn the heating on, it starts up, thinks for a minute, fires the burners, they go off, and start heating stuff up. Then no blower turns on. It continues to hum, and then it starts smelling bad up stairs, and the outgoing air duct is super hot to the touch.

Plumber101 10-08-2009 08:23 PM

What happens when you turn the thermostat fan control to ON instead of AUTO

Does the fan come on?

wavelength 10-08-2009 09:33 PM

same behavior
The exact same behavior occurs. i know the blower works, i just tried it on AC again.

Dennis1973 12-21-2009 07:31 AM

I'm having the same exact issue with my HVAC unit, i changed my blower motor this summer and it worked in AC mode.

I found out about two weeks ago it won't kick on with heat. My gas heat still kicks on with the T-stat, but i have to manually turn my blowers on (it still works if I turn it from auto to on)

Any ideas? Mine is a 1970's Janitrol unit but I figure it is a common issue.

Final Final 12-31-2009 09:38 AM

Sounds like you may have a bad stat or you may have accidently broke a wire or pulled one off when you were working on the humidifier.....

Did you try to jumper between R and G? the R terminal is 24 volts to power the low voltage and the G terminal starts the fan.

TJ_in_IL 12-31-2009 10:17 AM

Is the fan blower motor a multi-speed? The lead that powers the blower motor in heat mode may have dislodged when you were in there. There are usually two different speeds, one for cool, and one for heat. In the fan over-ride mode, the motor usually come on high, or the same as cool.
Check for a loose or disconnected wire.

Final Final 12-31-2009 04:06 PM

Good point for Dennis, wavelength,etc....if they changed the motor but did not install the proper one or like you said bumped one of the wires off the terminal they will have trouble.....also, if you are running the furnace in heat mode with the motor operating in the cooling mode speed you may encounter air flow issues....too much or not enough air.......and this can in the long run lead to heat exchanger issues of either rusting because you have too much air and are running a low temp rise, or if you have too little air flow you can overheat the heat exchanger and crack it because the temp rise is too high....
Just some random thoughts on air flow when you start talking motor speed, etc.


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