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(Help) Combustion air blower kicks on and off after furnace reaches set temp

(Help) Combustion air blower kicks on and off after furnace reaches set temp

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  #1  
Old 10-27-13, 03:58 AM
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(Help) Combustion air blower kicks on and off after furnace reaches set temp

Furnace & the Furious - Imgur

I have an Armstrong natural gas furnace with a electronic ignition (model guj075d10-1a) and a Honeywell digital thermostat (32002418-001 REV). The furnace was installed in 1994. It will start normally and complete a cycle without any problems. Once the set temperature is reached the burners turn off and the blower fan stays on for a while, as they should.

However, a couple seconds after the burners turn off the combustion air blower kicks on for 2-3 seconds then off for 2-3 seconds. The gas does not open (can't smell anything) and the ignition does not attempt to light (there is no clicking). The combustion air blower will continue to cycle on/off until the thermostat calls for heat again, due to either the house temperature dropping or by raising the set temperature.

Possibly relevant:
New thermostat installed by professional (previous thermostat and weird had been cut and removed when we purchased house). He checked operations w/o gas on (gas company hadn't been out yet).
There is a wire that appears loose/partially severed. It looks to be a ground for the combustion air blower.

Already tried:
Turning off, unplugging waiting 10+ min then turning back on.
Replacing filter.
Replacing thermo coupler.
Checking for loose wires.
Removing and clearing out hose between pressure sensor and motor. Also checked for leaks in hose.
General cleaning.

Do you have any idea what could cause this? If so how can i correct this issue. Any thoughts/advice is appreciated, thanks!
 
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  #2  
Old 10-27-13, 06:11 AM
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Since you mentioned a problem with the tstat wire I would have all new thermostat wire pulled. Any stretching or damage on a tstat wire can cause the wires to partially short out and cause ghost symptoms just as you describe. Usually takes only a few minutes to pull a new wire, that is where I would start on this. Cheap/Easy and a darn good chance of fixing the problem.
 
  #3  
Old 10-27-13, 11:06 AM
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Thanks for the suggestion, but the problem wire wasn't a tstat wire. It was within the unit, I provided a close up picture of it (green with yellow swirl). Would you still suggest replacing the tstat wire?
 
  #4  
Old 10-27-13, 11:48 AM
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That green ground wire lug should be cleaned up. I see a lot of rust in your unit. A loose/intermittent ground can cause many problems. Check the grounds screws around the control board too.

Here's another similar thread.

http://www.doityourself.com/forum/ga...at-called.html
 
  #5  
Old 10-27-13, 12:17 PM
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Thanks for the link, I'll clean up the grounds and try adding another relay as suggested in the other thread.
 
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