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Central air/heat blower stays running..
I have a central air/heating system and the blower will not turn off even with the thermostat in the OFF position. It is gas heat and electric air but I dont think that matters. Its dark now, but Ill go up and check it in the morning, but i ASSUME, that the thermostat sends signal/power to the blower, or a fan relay, where it then uses house power to run. It is an older system without any of the new electronics stuff the ones of today have. Sound right?
I think i read its a 24 volt system?? But I would think the fan runs on 120 typical house current, but something is 'telling' the fan to run, and it is, so i can eliminate the house power to the fan. I have located the source wire from the thermostat to the blower. What voltage range should i be checking for? 24 vdc? I would think if I have power there, then the thermostat is bad, but if not, then the blower relay is bad.. Anything to add? |
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12-01-2010, 07:07 PM
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Parrothead member
Join Date: Jul 2003
Location: Monmouth county, NJ USA
Posts: 13,831
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Bad thermal limit switch
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Vinny Red '86 944, 05 Ford Super Duty Dually '02 Ram 3500 Diesel 4x4 Dually, '07Jeep Wrangler '62 Mercury Meteor '90 Harley 1200 XL "Live your Life in such a way that the Westboro Baptist Church will want to picket your funeral." |
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12-01-2010, 07:13 PM
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Registered
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Quote:
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A nose heavy airplane flies poorly, a tail heavy plane flies once. |
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12-01-2010, 09:01 PM
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Registered
Join Date: May 2002
Location: St Louis
Posts: 4,211
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Is there a switch on the thermostat that says on-auto?
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Rick 88 Cab |
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12-01-2010, 09:12 PM
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Unconstitutional Patriot
Join Date: Apr 2000
Location: volunteer state
Posts: 5,620
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You can isolate the thermostat by removing the "red" wire. This supplies 24volt AC to the thermostat.
If the blower continues to run, it's being triggered by the circuit board. The circuit board may be telling the blower to run continuously if the limit switch is bad. |
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12-02-2010, 04:11 AM
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Unconstitutional Patriot
Join Date: Apr 2000
Location: volunteer state
Posts: 5,620
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Also, check for voltage at the transformer. Again, ~24 Volts AC. Also, check the circuit board for error codes.
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12-02-2010, 04:15 AM
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Unconstitutional Patriot
Join Date: Apr 2000
Location: volunteer state
Posts: 5,620
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Err, forgot you may not have a circuit board. Older furnaces have a mechanical switch in the furnace plenum. That may need adjustment or may be bad. You'll need to check for continuity.
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12-02-2010, 04:17 AM
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ok, got in there and looked around. Appears to be a bad circuit board. I can tap on the relay and the blower clicks on and off. The relay is made onto the circuit board. I got the part number called the local distributors and of course they wont sell to the public and the local companies all wanted @ $325 to come out and replace it. I told them I had the part off in my hand and they will not do it that way.
This is such CRAP.. anyway, found it all over the internet for $49.00 and it will be here tomorrow.. This is the old one. The new one is an updated part with more electronics on it.. 
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12-02-2010, 11:09 AM
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78 Porsche 911 Turbo
1972 porsche 72 rsr clone
1995 porsche 993
1995 porsche 993
1990 porsche C2 911
1966 porsche 911
1984 Porsche 911
2003 Porsche 996
1979 Porsche 911SC
