Skamper Duo-therm Furnace WAS working, now the pilot wont stay lit

[BRWHUNTER]

I have an 88 Skamper 082s that I purchased last month. Ive taken it out a few times so far and the 66117 furnace has been working nicely. But today in the garage I couldnt get the furnace to work. I now cannot keep the pilot lit when I release the pilot gas valve button. FYI I did just change out the thermostat, when the new thermostat is turned on the fan come on but i cannot get the gas valve selector button from Pilot to On without the pilot going out. I am getting a millivolt reading out of the thermocouple. The little temperature bulb on the inside of the furnace wall (temp limit switch?) reads an ohm so it is closed at room temp which i assume is correct.

Any ideas what im missing or what i need to check next? I guess I could put the old thermostat back on (it turns the furnace on but doesnt control the temp around the set temp, instead i use it only as on/off control) but i dont think that is the problem. Please help, up here in alaska a furnace is really important

 

[uriedog]

Is the pilot strong? or a weak fissle. Could be a clogged up feed or regulator.

You can also ensure the sail switch is making when the fan turns on. it does not take much of a blockage in the air flow to stop it

 

[dwh]

How many millivolts from the thermocouple? Should be around (IIRC) 20mv. Also the tip that screws into the valve can get oxidized, making a crappy connection.

 

[BRWHUNTER]

Ok. The pilot is strong. I haven't checked the sail switch yet, would it keep the pilot from staying lit? I was thinking it would just keep the main burner from lighting.

I held up a lighter to the thermocouple for a short time and it got to 10mV but I see now that that wasn't enough time for a thorough check. I thought that if it was bad I wouldn't see any voltage.

 

[dwh]

Dunno, I'm an old electrician, not an old HVAC guy, but I don't think it's strictly "works or it doesn't". Seems to me they can get weak and/or intermittent.

 

[BRWHUNTER]

Thanks guys. I just found a YouTube that indicates that thermocouples can die slowly and do not necessarily die completely (unless one of the wire breaks of course). I also think dwh is correct is thinking that corrosion is making my connection worse. When I get home I will reinstall the old thermocouple after cleaning it's connection cap (sorry don't know the name? But I'm talking about the part that plugs into the gas valve assembly not the pilot reading portion) then I will probably buy a new one this weekend.

Thanks for the help. And I'll post my results later

 

[BRWHUNTER]

Update. Pulled the thermocouple back out but left it installed next to the pilot. This time I checked the max mV produced from the pilot... 12mV almost 13. This is significantly less than the 18-30 necessary to actuate the pilot solenoid . There wasn't any corrosion on the thermocouple. I think this is great news! Contingent upon being able to find a replacement thermocouple. Any advice on replacement? Right now I'm thinking a normal 24v universal replacement may work even though the thermocouple heat sensing probe is usually twice as long as the original. It looks like a longer probe will clear every that could be in the way. What do you guys think?

 

[dwh]

"24v universal replacement"? What? You mean 24"?

I'd imagine anything that would actually fit would work. Even with a big bulb, it's not like a pilot flame would heat the entire bulb surface anyway.



According to this:

http://www.ntpdistribution.com/pdf/via/41-duothermqkchart1of2.pdf

If you wanted an exact replacement, you'd need a 41-0645, which can be found here:

http://www.rvshop.com/Duo-Therm-T-Couple_p_68680.html

 

[BRWHUNTER]

Replaced the thermocouple. No change. I cannot hear the automatic pilot solenoid valve actuate, and I did not listen for it when it was working. Should I be able to hear it?

 

[dwh]

Automatic pilot? I thought is was manual?

Don't have time today to suss out a manual for it and look it over. Is yours a 66117-what? 006? 007?

 

[BRWHUNTER]

The furnace is a 66117-009.

Manual pilot. In a manual I found they described the solenoid as "automatic"

Today I fully removed the furnace. Pulled out the solenoid and put the torch to the thermocouple while it was connected to the solenoid. At 20mV (closed circuit not open) the solenoid did NOT pop open by itself as I had assumed but when I pushed the valve open with my finger it opened and stayed open due to the tiny electromagnet the thermocouple powered. Now my assumption is that a combination of pressure from the gas and the pressure applied by the gas push button selector switch supplies the force necessary to bring the solenoid valve close enough to the magnet to make the connection that keeps it open when energized.

My assumption now is that the gas pressure is too little to help the solenoid open,

Or the push button gas selector switch and pilot override button does not compress far enough to make the solenoid connection

Or my pilot is not producing the necessary milliVolts to power the electromagnet and keep the solenoid valve open against the fail close spring force.

Thanks again for the help guys I've been having a blast troubleshooting this furnace. Really would like to get this thing working by the weekend though. Hoping to get some more halibut shore casting and king salmon trolling in this weekend from the comfort of a warm camper

 

[brian90744]

Go back to square one.... remove the new thermostat and check if it stays lit????=brian

 

[BRWHUNTER]

Just got the pilot to stay lit. New thermocouple installed, furnace on my kitchen counter, propane hooked up from bottle through regulator then directly to furnace.

I think what's going on is first that the thermocouple was weak and intermittent

Second that when the solenoid was properly energized yesterday with the new thermocouple installed that I did not press the gas selector switch deeply enough.

Third, I think my LP tank feels lighter today and the connection from the regulator to the camper propane header did not feel tight enough so I think there may have been a small propane leak after the regulator which could have dropped usable pressure.

 

[dwh]

So the furnace works. Yay. Nice job!

Just an offhand question...Is the regulator you're using on the test bench the same regulator that is in the camper?

 

[BRWHUNTER]

Ok furnace is reinstalled in the camper and is cycling on and off nicely with the new thermostat.

My bench regulator was the same one the camper uses. I replaced it when I bought the camper because the old one's spring had rusted out.

I am pretty sure the problem was originally the thermocouple... Then I hadn't had enough time to play with the combination gas valve switch/button and it was rough making it difficult to depress. Now that I've tinkered with it it depresses nicely and I can feel the solenoid pick up the valve (and I can hear it drop the valve when it gets too cold)! Awesome. Thanks guys. I'll come back to this thread with a fishing pic for you guys later.