Shop Heater Diffuglity

[Andy Hoyt]

My turn to ask the collective wisdom of the Creek a question about my shop furnace.

It's an old beat up propane fired forced air stand alone unit. Works great with minimal fuss - usually.

But it has now developed a cycling issue. The pilot light stays lit and the burner kicks in just fine; but the darn blower fan keeps cycling on and off. Normally, it kicks in and does its thing for a minute or so and shuts off. But now it starts up, blows for four or five seconds, and then shuts itself off. A minute later it repeats this and has been doing so all morning (and probably most of last night).

The shop is staying at the desired temp which leads me to guess that the burner is firing far more than it normally should/would; which leads me to further guess that I'm using up far more propane than I should.

I've blown all the dust off of and out of the unit (do that routinely) and this hasn't helped. My guess is that there's a relay thingie that has gone wonky, but I'm clueless as to know which one, where it is, how to fix it, or whatever else might be the problem. I'd hate to call the repair guy if this is something really simple. Yup - feel free to interpret that as me being cheap.

Help! Thanks, Andy

[Joe Pelonio]

My turn to ask the collective wisdom of the Creek a question about my shop furnace.

It's an old beat up propane fired forced air stand alone unit. Works great with minimal fuss - usually.

But it has now developed a cycling issue. The pilot light stays lit and the burner kicks in just fine; but the darn blower fan keeps cycling on and off. Normally, it kicks in and does its thing for a minute or so and shuts off. But now it starts up, blows for four or five seconds, and then shuts itself off. A minute later it repeats this and has been doing so all morning (and probably most of last night).


When my home furnace did that it was the regulator, it determines whether the burner is on, if not the fan stops. There was a sensor that sticks in the flame and tells the regulator that it's hot so there's a flame. If either that sensor is burned out or the regulator is bad, then it thinks there's no flame.
Yours may operate the same way, and if so, either the regulator or sensor or both together may be available from a parts supplier.

[Kyle Kraft]

Pilot lights up, burner lights and stays on, but the fan turns on and off? If the burner was cycling I'd guess a plugged air filter causing the heat exchanger to overheat and cut out the burner on the high limit.

[Al Willits]

Without knowing which furnace you have, I'll use generalities here.
The limit should cycle the burner.
A fan control will cycle the blower motor
This may be one unit or seperate.
Do you know what kind of fan control you have?
It may be possible to jumper this and see if its the fan control or the motor itself.
Al

[Andy Hoyt]

Thanks, guys. The three of you jogged a memory I had from a few years ago when I actually did spring for the guy to come out and jump start this thing.

I recall that he removed one of the tubes (maybe both, but I think the one I arrowed to in the first pic) sticking into the burner chamber and scratched the end of it up with some sandpaper, and everything worked okay after that.

I've got the beast turned off and cooling a bit right now and will attempt this shortly.

Oh, and it's a 22 year old Sears unit, which I guess means that it could have been built by anybody. But am hoping that parts are common enough.

Hope this helps some more.

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EDIT: Nope - that didn't work. Al - no idea as to the type of fan control I have. Not even sure what it would look like.

Andy - who sure wished he wasn't so stupid on this stuff.

[Al Willits]

Not stupid Andy, ya just don't know....
Can ya pan up a bit on the furnace, there any kinda controls up a bit??
To be clear, does the fan/blower cycle or does the burner??
Looks like a thermocouple style ignition system, so I don't know what he would have cleaned, maybe the sparker to ligh the pilot.
I'm not at work or I could maybe figure out who made it, whirlpool made a bunch for them back about then.
Al

[Andy Hoyt]

Thanks for coming back to this Al.

This first pic is the whole unit. Ignore the wierd shape - it's two pics stitched together.

The second pic is a close up of what's behind the unit's middle panel (all three are removed in the first pic). I found a label down in the bottom of the unit that speaks to something called a Thermocouple and I believe that this might be just that - if I understand the less than ideal wording on the label.

Hope this helps. Gotta step out now til about 10 PM. But I'll be sure to return. Thanks.

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[David G Baker]

Thanks for coming back to this Al.

This first pic is the whole unit. Ignore the wierd shape - it's two pics stitched together.

The second pic is a close up of what's behind the unit's middle panel (all three are removed in the first pic). I found a label down in the bottom of the unit that speaks to something called a Thermocouple and I believe that this might be just that - if I understand the less than ideal wording on the label.

Hope this helps. Gotta step out now til about 10 PM. But I'll be sure to return. Thanks.

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Andy,
If you can trace the wiring on that button you may find that it is connected to the fan motor. Don't remember what it is called but it looks like a temperature controlled switch. When the heat chamber reaches a certain temperature that button will turn on the fan. They do go bad once in a while. If you determine that this is the fan control you should be able to get a replacement at your local heating/air conditioning shop.
If it is not the fan motor control then it is a switch that will shut the unit down if the heat chamber over heats.
Let us know how it turns out.
David B

[Al Willits]

There called clix-ons or probably more correct snap action limit/controls, clix-on is probably a brand name.
Can you read the white part of the control?
This almost looks like a limit/fan control together.
As suggested, can you find the wiring diagram?
If we can figure out which is the fan control, ya can jumper it out for temp useage.
But ya definitely don't wanna jumper the limit.

Al

[Andy Hoyt]

I'm back.

Lemme go look

[Andy Hoyt]

Okay – I hope this pic makes sense to you. It shows where all the wires from the thing (thermocouple?) in the middle of the unit lead to.

The data imprinted on that thing is as follows:


312350
T-D-D 60T11
HQ507847TD
8714
L205 3QF


Having trouble uploading the pic - please stand by

[Al Willits]

L205 would be the limit part, picture of wiring diagram might help
Al

oh...is there another one of them round things?
Maybe follow the wires from the blower motor

[Andy Hoyt]

One more time

[Mike Sheppard]

Andy
To fan is controled by a limit switch in the heat exchanger, it should be about 1 1/2 x 3 x 1 1/2". Remove the cover and you will see dials with #s. Pull it out and it will have a coiled tube going into the unit. Take it with you to a furnace shop to be sure you get the right one (I think the last one I bought was about $12). If it was the thermocouple the burner would not come on.
Mike

[Andy Hoyt]

Thanks to all who pitched in with their advice. The shop is toasty warm again and the furnace is now behaving properly.

I ended up swapping a few PMs with Al and he guided me through the troubleshooting and repair process.

Yup - it was the fan control limit switch and it cost me a whopping $7.29 to replace it.

I imagine that Al's consulting bill will be slightly more.

I owe ya one, Al. Not sure how, when, or where - but it'll happen.

Thanks.

[Al Willits]

Ahhhhhh Andy, remember that drum sander I was talking about in my other post......:D :D
Just kidding, glad to help.
Al