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Old 12-26-2011, 10:26 AM   #1
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Heil furnace blows cold air


I have read about thrity posts on this ofrum about items that sound similar to my problem. Here are my details:
I don't know the model number. I can't find one anywhere ont eh furnace.
It is in my attic. The AC unit is outside.
I found numbers on two parts on the system.
The unit seems to have two sides.
On the left is the fresh air intake, with a large motor/fan. When I remove the cover panel, their is a safety switch on the bottom right.
This side houses a large circuit board.
On the right side, behind it's access panel are the burners, what I presume is a gas valve (Is this the 'smart valve' I have been reading about?) and an electronic module.
Here are the numbers I found related to these two items:
Code:
The 'valve' VR8204M 1075 (with a sideways 6 at the end)
Reg 3.5 ADJ
3-5 Range
24V 60 HZ
HQ1005597HW
9922 D4C2V

The electical box shows:
MPLS.MN55422
S8600M 1005(1)
Continuous Retry
HQ1011449HW
992A
Here is what I observe:
A small black wheel spins on the right acess panel side that seems to have what appears to be a brown vacum tube running to something above it.
To the left of it are a series of horizontal tubes that the flame burns iside of it.
After a period of about 30-40 seconds I here a loud clicking, the pilot light ignites, and then each of the horizontal burner tubes fills with a ble flame. This flame ignites after about 1 second from the sound of the click.
The flames burn for 3 seconds, then the flames turn off.
In the mean time the fan on the left side is still running (cold air comes out of the vents in teh house) and the small black round disk previously described continues to spin.
My guess is that the small round black disk that I spinning is some fan (inside) that drwas the blue flames through the burners, providing a direction draft for the flames.
The metal 'flue' or exhaust running up through my roof is warm to the touch, but not hot.

Any and all help is appreciated.
If useful, I can provide phot's or video of what is going on.
I would love to know ehere to find the model number.

Thank-you,
--Bruce

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Old 12-26-2011, 10:39 AM   #2
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Heil furnace blows cold air


You have a dirty flame sensor......its in with the pilot and the spark electrode, remove it and clean it with sand paper........should be all good after that.

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Old 12-26-2011, 10:52 AM   #3
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Heil furnace blows cold air


I will do this right now, and post my results Sir.
--Bruce
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Old 12-26-2011, 11:56 AM   #4
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Heil furnace blows cold air


I am not sure if I cleaned the right part.
I removed three sheet metal screws. Two held a bracket to the furnace, and one held the igniter assembly to the bracket.

The igniter assembly has a blue wire, a small gas line.
I see three parts to the igniter assembly.
My guess is:
Electrode, for creating the spark. Small thin 'wire'.
A v shaped bottom portion that I guess diverts the gas flow upwards from the gas line outlet towards the electrode.
A two pronged 'claw' that descends into what would be the flame.
It is 'pressed into the assembly.

I cleaned the claw portion, which frankly didn't seem to be dirty. I guess since it is natural gas 'dirty' would be a relative term. I used rough grit emery paper.

I could bring a dremel to it with a sand paper tube to get it cleaner. I thought I would post my results first, and make sure that I am cleaning the correct part.

I tried something else that had a result, though perhaps a meaningless one.
I read some posts about cleaning a rubber tube out.
I have one such (silicone?) tube coming from the small motor on the right side above, down to a small diaphragm below it. The reddish/brown colored tube is maybe 6 inches long. it is clean, no dry rot. It looks good.
I remove it from the top, and sucked on it gently. I heard a noise with an almost like a gurgle type sound. I tried it the other way to no effect.
I let the furnace start again. So long as I provided vacuum, it remained burning until maybe two minutes went by, and then it shut off. The vacuum did not remain rather I had to continually draw in with my mouth while breathing with my nose. It would say it allows the vacuum to dissipate. Either it is a leak, or it is by design. This diaphragm on the bottom has a blue ire that goes to the igniter assembly. I will assume that this diaphragm is what determines (at least in one way) whether to allow the igniter to function. Perhaps it is the way to determine if the motor is running that draws the gas into the three horizontal burn tubes.

--Bruce
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Old 12-26-2011, 12:07 PM   #5
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Heil furnace blows cold air


That is your draft inducer motor to pressure switch tube. Remove the tube completely and clear both ports where the tube connects to, one on the motor and one on the switch, with the use of a straightened paper clip.

You're problem is that the pressure switch is not remaining closed. It could be that the draft inducer is failing which does happen, it will work (turn on) but not produce enough suction to close the pressure switch, but 9 of 10 times it's sediment from condensation and the likes blocking those ports.

It happens frequently and the paper clip is the known and trusted tool in the field for the job.
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Old 12-26-2011, 12:26 PM   #6
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Heil furnace blows cold air


My Wife says to tell you that she loves you. :-)
On the diaphram side, it felt clean.
On the draft inducer side, I could niether draw nor blow air.
When I inserted the paper clip it only went in about 1/4 inch and stopped. It was completely blocked. I scraped around all sides inside the port until I felt no more residue. The blockage had the consistancy of a calcium deposit.
Thank you for your Christmas Present of sharing your knowlege.
This will now become a seasonal bit of maintenance for me.

--Bruce D. Meyer
Columbia, SC.
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Old 12-26-2011, 01:11 PM   #7
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Heil furnace blows cold air


The both of you are more than welcome.

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