Combustion blower & fan motor won't turn off


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Old 12-06-15, 02:39 PM
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Exclamation Combustion blower & fan motor won't turn off

Tempstar A/C & furnace unit PGME60G1507
Honeywell control board ST9120C 5005

A/C & furnace were not running for about 2 months.
Noticed fans (combustion blower & indoor air circulating fan) suddenly running with thermostat shut off. Removed power at main breaker but they restart after turning breaker back on.
Disconnected all thermostat wires, still runs.
There is 24v from transformer to control board but nothing coming out to thermostat.
Replaced control board but immediately running when I restored power.
I even tried a new thermostat. NG.
Will these fans run if my gas igniter or thermocoupler fail?
I have been running the gas logs in fireplace so I know I have gas.
Any help out there?
It's getting cold at night's even here in SC.
 
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Old 12-06-15, 02:53 PM
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Welcome to the forums.

It's getting cold at night's even here in SC.
It's certainly good you checked it now when you need it.

Is this a self contained packaged unit ?
If the inducer and blower fan is running without a call for heat then you may have an open safety switch.

You're going to need a voltmeter. If you don't have one you'll need to get one. Even a basic analog one from the Depot will be ok.
 
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Old 12-06-15, 06:15 PM
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PJmax,
Thanks for the reply.
It is a self contained package manufactured by ICP (International Comfort Products) for TempStar.
Yes I have a meter & know how to use it.
The only safety switches I see are what they list as a "Rollout Switch" & a "Main Limit" switch, one of which is located above the openings of the gas burner tubes. The other, wired in series, is somewhere inside the circulating fan housing/cabinet. I don't know which is which nor have I opened the cabinet to locate the switch in there.
I guess I need to hook the meter up to these tomorrow to see if they are any good.
 
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Old 12-06-15, 06:18 PM
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Right off the bat... check the transformer for 24vac.
 
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Old 12-06-15, 06:22 PM
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There is 24v from the transformer to the control board but nothing coming out on the Red wire/terminal to the thermostat.
 
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Old 12-07-15, 07:35 AM
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The link below should be the manual for your unit. There are several wiring diagrams in it which makes servicing a little confusing without being there. There will be an accurate wiring diagram posted somewhere on your unit. Usually on the back of one of the service doors.

I see one high limit stat which is self resetting and I see one rollout switch.

With your unit.... if the flame rollout switch is open.... the blower and inducer will run and the 24vac to the R terminal is interrupted. That safety switch is near the burner opening and has a red pushbutton on it. Try resetting that switch.

If that was tripped you will need to observe the burner process when it lights. You may have a flue/vent issue.

icp indexing/documents/086477/46208100100.pdf
 
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Old 12-07-15, 03:23 PM
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Pete, you are are a life saver. The Rollout switch was tripped & I didn't realize it was a manual reset. After resetting, the heat came on properly on demand. Found out most of the supply registers had been mysteriously closed (wife denies knowing how there got closed) & the return filters were clogged. Changed filters & opened all registers and I'm good to go.
Just wish I consulted this forum before spending $200 on new board & thermostat.(Now I need to put old board back in & list new one on eBay)
Thanks again for pointing me in the right direction & the link to the manual.
 
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Old 12-07-15, 03:55 PM
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A plugged up air circulation system such as you describe will commonly cause the high temperature limit switch open. It wont typically cause a flame rollout switch to open.


My suggestion is to carefully observe the burners and flames in the area surrounding the flame rollout switch and look for flames that are reaching out in front of the burners where they would come in contact with that flame rollout switch.

Flame rollout is most commonly caused by heat exchanger that are getting plugged with soot, or sometimes rust. So you can look for evidence of black soot that might be accumulating at the bottom of the heat exchangers or on top of the burners, too.
 
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Old 12-07-15, 04:17 PM
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In addition to the excellent advice from SP ..... since it's a packaged system it has its own flue vent hood. Be sure to check that for nests and other blockages.
 
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Old 12-07-15, 05:05 PM
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Good advise guys.
I'll check into those tomorrow after work.
Whats the best way to clean a partially plugged tube if that's what I find?
Can you gently blow into the burner tubes with compressed air to clean them or will that blow them out/up?
 
 

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