Furnace blower comes on and off and on...

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Old 04-30-10, 09:38 PM
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Furnace blower comes on and off and on...

Hi,
I have a Carrier Weathermaker 8000 that is acting up. When I turn the thermostat to heat, the blower goes on right away then in about 30 seconds the blower turns off. The furnace stays on full flame. Then about 30 seconds later the blower goes back on, then off again.

Sometimes it stays blowing for 5min. But it is taking a long time to heat the house this way.

My wife says she has seen the thermostat just go blank, it is electronic, but has no batteries.

I'd replace the thermostat, if I knew that was the problem. Is there any way to jumper the thermostat and see if the problem is in the thermostat or in the furnace?

Thanks,

Steve
 
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Old 05-01-10, 05:20 PM
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It sounds like a fan timer or other fan relay problem. Or possibly a loose wire connection at the board, or motor wiring issue, that acts up on a timely clock-like precision, due to heat, that breaks the connection, til it cools back down.

You could run the blower constantly, for now, until you get this resolved. Set your stat to fan ON setting.

You could test(with a voltmeter) to see if you lose power or not at your HEAT terminal on your board. That terminal is the hot wire hookup for the blower motor.
 
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Old 05-01-10, 08:28 PM
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Assuming you have single-stage heat, if you want to short the tstat to see if its the tstat or something else, connect the Red (source) with the Green (fan) and White (heat). That should simulate your tstat calling for heat and fan continuously.
 
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Old 05-02-10, 10:02 AM
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It is a 2 stage heat. How would I over ride the tstat ?

I pulled the front off yesterday and looked for obvious frayed, bent or loose wires, found nothing.

I guess I'll have to call in for service...

Thanks

S.
 
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Old 05-02-10, 01:52 PM
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Jumpering between R and W bypasses the stat. If you do this in the handler where the stat wires all hook to a terminal strip, you eliminate not only the stat as a culprit, but the wires that run between the stat and handler, as well.
 
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Old 05-02-10, 03:24 PM
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I jumpered red and W1 at the tstat to start my debugging. Much better. The furnace turned on, no blower for a little while, then the fan kicked in and stayed on.

I guess the tstat is flaky. Maybe time to get a programmable one. Thanks for the help. I can easily replace the tstat myself.

S.

Beer 4U2
 
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