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Discussion Starter · #1 · (Edited)
Hey guys
I have an 1982 counterflow gas furnace in the shop that i'm havind a problem with and hope someone could help me out on what might be.
First off let me say that i'm a remodeling contractor and have been kicking around the trades for about 26 years. That being said, i've had occasian to do minor repairs on furnaces, though I have an HVAC contractor for most of the large projects. Unfortunatly he's also out of down till the first of the year.
Anyhow, the problem.
On call for heat everything works as it should, electronic ignition is immediate and so is the pilot flame. Thermal sensor is working as the gas valve opens after 40 seconds or so and the burners fire up.
Problem is that the burners will stay lit for about 5 to 6 seconds and there is an audioable click and the gas shuts down. After another 40 seconds or so the cycle starts over with the same results.
The system is really simple on this unit, basically the gas valve, spark ignitor and the limit switch. I have looked at the electrical schematic thinking ther was a secondary 'no flame' sensor but there is not.
I'm in the midst of assembling 775 square feet of laminate tops and the no furnace in the Chicago region is not going to work.
Any help would be appreciated.

Thanks
 

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woodbutcher said:
Hey guys
I have an 1982 counterflow gas furnace in the shop that i'm havind a problem with and hope someone could help me out on what might be.
First off let me say that i'm a remodeling contractor and have been kicking around the trades for about 26 years. That being said, i've had occasian to do minor repairs on furnaces, though I have an HVAC contractor for most of the large projects. Unfortunatly he's also out of down till the first of the year.
Anyhow, the problem.
On call for heat everything works as it should, electronic ignition is immediate and so is the pilot flame. Thermal sensor is working as the gas valve opens after 40 seconds or so and the burners fire up.
Problem is that the burners will stay lit for about 5 to 6 seconds and there is an audioable click and the gas shuts down. After another 40 seconds or so the cycle starts over with the same results.
The system is really simple on this unit, basically the gas valve, spark ignitor and the limit switch. I have looked at the electrical schematic thinking ther was a secondary 'no flame' sensor but there is not.
I'm in the midst of assembling 775 square feet of laminate tops and the no furnace in the Chicago region is not going to work.
Any help would be appreciated.

Wood does this unit have a power venter attatched to it, or does it have an inducer motor on it IE 80% unit?

Try to remove the sensor and sand paper it with some emery cloth to clean it.

The ignition system sounds like a Honeywell S 86-U 24 Vlt, it may be bad, do you have a vent damper on this system? If so that also could be the problem.

Vent dampers open and make contact with the gas train, if they screw up they can shut a system down.

Check the roll out switch and down draft switch for open/close during the start up and shut down times.

Does the time increase at cold starts? if so try the above mention switchs as they pertain to flue problems.

Good Luck
Bernie

Thanks
 
G

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HVAC Contractor

Is it 3 wire pilot burner?
Then check if yellow or green wire looses power(24V)
If green looses power then replace the pilot burner( green wire confirms existence of
pilot flame), if problem with yellow then check limit switch ( its better to bypass it for
the time of troubleshooting, means short both terminals with jumper wire)
If there is no 24 V lost for all perid of time then replace the gas valve(also make sure
that 24 V is always present on gas valve).

Good luck
[email protected]
 

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As your pilot burns against the flame proving mechanism it sucks in air to breathe. Any dirt in the air will start clogging up the air inlet and the pilot orfice. This makes the pilot flame weak and it won't prove flame.
 

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On call for heat everything works as it should, electronic ignition is immediate and so is the pilot flame. Thermal sensor is working as the gas valve opens after 40 seconds or so and the burners fire up.
Problem is that the burners will stay lit for about 5 to 6 seconds and there is an audioable click and the gas shuts down. After another 40 seconds or so the cycle starts over with the same results.

Here's the dope woodbutcher;

Your flame senoer is dirty scrpae it off , note do not use sand paper -- scrpe it like with a knoef balde, and that puppy will run like new-- hey have a great day! But just a word of advice stay to carpentry all of us know about this-- it;s basic , hope this was not for a paying client!
 
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