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Old 01-11-2012, 01:04 AM   #1
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Cold air from gas furnace. please help


I have a Gas furnace that blows cold air sometimes. The heater will work fine for a while and then cold air is coming out of the vents and the fan never shuts off. the thermostat is set to auto mode and if I turn the temp dial down below the room temp the fan shuts down, and if I raise it up again the fan comes on right away without the heater turning on at all and there is no flame when I look through the little flame window and cold air comes out of the vents. I can get it to work again by unplugging the furnace power plug for a few minutes and leaving the heater off. Then the heater comes on and I can see the flame through the window. It shuts off two to three times during the day or night. I replaced the filter and that didn't help either. I have included some photos.Please help
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Cold air from gas furnace. please help-dsc_0400.jpg   Cold air from gas furnace. please help-dsc_0401.jpg   Cold air from gas furnace. please help-dsc_0403.jpg   Cold air from gas furnace. please help-dsc_0402.jpg  

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Old 01-11-2012, 01:29 AM   #2
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Cold air from gas furnace. please help


LETS TRY REMOVING AND CLEANING THE FLAME SENSOR FIRST, if that don't work we will dive deeper into it......the flame sensor is the white porcelain base to the rear and right of the burner box on pic. #3, simply remove the screw, remove the sensor, clean it with sand paper or a scotch brite pad, put it back in and all should be well. We are starting with this coz this is the problem 90% of the time .also in picture #2 there is a black cap laying in the bottom of the furnace......it should be covering the hole to the left of were the flame sensor mounts.....


Last edited by harleyrider; 01-11-2012 at 01:31 AM.
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Old 01-11-2012, 08:47 AM   #3
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Cold air from gas furnace. please help


the reason your blower won't stop is because you have it in auto mode.
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Old 01-11-2012, 09:20 AM   #4
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Cold air from gas furnace. please help


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Originally Posted by harleyrider View Post
LETS TRY REMOVING AND CLEANING THE FLAME SENSOR FIRST, if that don't work we will dive deeper into it......the flame sensor is the white porcelain base to the rear and right of the burner box on pic. #3, simply remove the screw, remove the sensor, clean it with sand paper or a scotch brite pad, put it back in and all should be well. We are starting with this coz this is the problem 90% of the time .also in picture #2 there is a black cap laying in the bottom of the furnace......it should be covering the hole to the left of were the flame sensor mounts.....
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Old 01-11-2012, 09:22 AM   #5
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Cold air from gas furnace. please help


The blower runs continuously when the unit faults due to the dirty flame sensor. It has nothing to do with the thermostat fan switch
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Old 01-11-2012, 10:57 AM   #6
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Cold air from gas furnace. please help


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the reason your blower won't stop is because you have it in auto mode.
That makes absolutly no sense what so ever.
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Old 01-11-2012, 09:34 PM   #7
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Cold air from gas furnace. please help


I will clean the sensor and put the cap back on and let you all know if it worked in a couple of days. Thank you all very much for quick and response to my post.
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Old 01-11-2012, 10:09 PM   #8
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Cold air from gas furnace. please help


Quote:
Originally Posted by hvac5646 View Post
the reason your blower won't stop is because you have it in auto mode.
please tell me where you learned that....makes no sense at all ....sorry.. sorry harley didn"t see your post...

Last edited by ben's plumbing; 01-11-2012 at 10:11 PM. Reason: someone else posted the same...
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Old 01-11-2012, 10:25 PM   #9
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Cold air from gas furnace. please help


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Originally Posted by ben's plumbing View Post
please tell me where you learned that....makes no sense at all ....sorry.. sorry harley didn"t see your post...
not a problem...........just waiting for.hvac5646b to explain why a motor will continue to run in this instance............

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Old 01-12-2012, 01:34 AM   #10
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Cold air from gas furnace. please help


Harley is right about it most likely being the flame sensor but you also have an led light on your board that might be flashing a diagnostic code that says why your furnace is locking out. It should be visable through a door grill or inspection port. If it is only accessable behind a blower door with a kill switch then you might have to tape that switch closed so you can access the led without the power shutting it off. That same furnace door will have a legend on it telling you how to interpret that led code. Close the blower door, run the furnace till the next time it locks out, open the door and carefully count the blinking sequence off the led.
Let us know what the led does and what the legend says is the fault.
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Old 01-12-2012, 09:58 AM   #11
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Cold air from gas furnace. please help


Quote:
Originally Posted by harleyrider View Post
That makes absolutly no sense what so ever.
The op said the stat was set in the auto mode.

here it is: " Cold air from gas furnace. please help I have a Gas furnace that blows cold air sometimes. The heater will work fine for a while and then cold air is coming out of the vents and the fan never shuts off. the thermostat is set to auto mode".

He first asked why his fan never stopped. I was not addressing the lack heat problem at that point.

And I would appreciate a little civility from you , sir.

Last edited by hvac5646; 01-12-2012 at 10:01 AM.
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Old 01-12-2012, 10:48 AM   #12
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Cold air from gas furnace. please help


Quote:
Originally Posted by hvac5646
The op said the stat was set in the auto mode.

here it is: " Cold air from gas furnace. please help I have a Gas furnace that blows cold air sometimes. The heater will work fine for a while and then cold air is coming out of the vents and the fan never shuts off. the thermostat is set to auto mode".

He first asked why his fan never stopped. I was not addressing the lack heat problem at that point.

And I would appreciate a little civility from you , sir.
If the stat is in the 'auto' mode, the fan should only come on with a call for heat. You're confusing 'on' (fan) and 'auto'. Many newer furnaces run the fan when there is a problem.
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Old 01-12-2012, 12:36 PM   #13
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Cold air from gas furnace. please help


Quote:
Originally Posted by hvac benny View Post
If the stat is in the 'auto' mode, the fan should only come on with a call for heat. You're confusing 'on' (fan) and 'auto'. Many newer furnaces run the fan when there is a problem.
Ehe....my bad. My head is in the clouds to day.

Thanks for the set-straight.
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Old 01-12-2012, 02:01 PM   #14
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Cold air from gas furnace. please help


90% furnace could be any number of things, flame sensor not too likely if it fires up at all and stays on. Drain problem? Check and make sure the venting has slope on it back to the furnace. If pipe is filling with water it will lock out the furnace. Pressure switch? Make sure you don't have any blockages in the venting. That little black plug may be causing problems, it needs to be put into the air intake on the side not connected to the venting pipe. This furnace can be vented out either side. Could be going out on high limit, check that all return air vents are free and clear not covered with furniture or whatever. Best to check the LED codes and post back for a more accurate diagnosis.
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Old 01-12-2012, 04:11 PM   #15
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Cold air from gas furnace. please help


What he said.

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