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| Re: [GMCnet] Help. 30 degrees out with snow. Furnace not lighting. [message #275585 is a reply to message #275550] |
Fri, 10 April 2015 16:16   |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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If the gas is turned on and present at the furnace and you can see a spark in the short time it is trying to light. The most likely cause is a faulty gas valve . They can have a burnt out coil or be stuck closed. I would vote for the latter. Connect a voltmeter to the coil and if there is 12 volts present at the coil when the igniter is sparking the valve is defective or stuck closed.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: [GMCnet] Help. 30 degrees out with snow. Furnace not lighting. [message #275606 is a reply to message #275550] |
Fri, 10 April 2015 20:45 |
Steve
Messages: 506
Registered: September 2013
Location: East Greenville, Pa
Karma: 1
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Bob,
Check each of the connections at the circuit board in the furnace. I was having similar issues and since I removed the circuit board and cleaned all of the connections it has worked correctly since.
1978 GMC Royal
Eastern Pennslyvania
1968 Chevrolet C20 396 Camper Special
1969 Chevrolet C20 Camper Special
1985 Buick Electra Park Avenue
1992 Camaro 25th Anniversary Heretage Edition Black
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| Re: [GMCnet] Help. 30 degrees out with snow. Furnace not lighting. [message #275912 is a reply to message #275587] |
Wed, 15 April 2015 11:48 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Senior Member |
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BobDunahugh wrote on Fri, 10 April 2015 15:18
I have 12.686 volts at the furnace when the blower is running. I also see spark for ignition. Sail switch is new. Now the furnace is out of it's own case. Plugged the 12 volt plug back in. Turned the thermostat up so the furnace came on. 8.52 volts to gas valve. Turned furnace off. Unplugged wires to gas valve. Gas valve had 36 OHM's. Hooked a 9 volt battery to gas valve. Nice solid click. Now what? Thanks. Bob
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Bob if the furnace didn't fire with the ignition sparking and a noticible click at the gas valve it either has no gas pressure at the valve or the valve is stuck closed.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: [GMCnet] Help. 30 degrees out with snow. Furnace not lighting. [message #275921 is a reply to message #275550] |
Wed, 15 April 2015 13:39 |
77Royale
Messages: 461
Registered: June 2014
Location: Mid Michigan
Karma: 6
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Had kind of a similar issue with my Royale and Suburban furnace back in Dec. Had gas, had spark, had power, NO burn. (I did clean the burner out and such prior to this which is a good idea anyway, Ran a standard hacksaw blade across all the burner slots and it cleaned up very well) I ran the furnace all winter here without any further issues after replacing the limit or hi limit switch. I hope this helps. for 20 bucks its worth a shot. and it sounds like you will be pulling the furnace anyway to clean it so the switch will go in no problem.
For those interested, This was a suburban NT 30M.
The limit switch part number is 230496. 20 bucks or so sourced locally at an RV place. I dont know if my old switch was ever replaced but the stampings on the back were the same as the new one I put in in December of 2014.
77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies, Patterson carb and dizzy.
Mid Michigan
[Updated on: Wed, 15 April 2015 13:41] Report message to a moderator |
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| Re: [GMCnet] Help. 30 degrees out with snow. Furnace not lighting. [message #275926 is a reply to message #275912] |
Wed, 15 April 2015 14:29 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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roy1 wrote on Wed, 15 April 2015 10:48BobDunahugh wrote on Fri, 10 April 2015 15:18
I have 12.686 volts at the furnace when the blower is running. I also see spark for ignition. Sail switch is new. Now the furnace is out of it's own case. Plugged the 12 volt plug back in. Turned the thermostat up so the furnace came on. 8.52 volts to gas valve. Turned furnace off. Unplugged wires to gas valve. Gas valve had 36 OHM's. Hooked a 9 volt battery to gas valve. Nice solid click. Now what? Thanks. Bob
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Bob if the furnace didn't fire with the ignition sparking and a noticible click at the gas valve it either has no gas pressure at the valve or the valve is stuck closed.
You have to follow the initial cycle closely. Mine started with the fan cycle, then the click, and then a momentary ignition. The thermocouple had to be cleaned and adjusted so that it recognized that it ignited and let it stay on. Sometimes you can hear if it lights, but it's better if you have the viewing window to watch if there ever is an initial flame.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] Help. 30 degrees out with snow. Furnace not lighting. [message #275969 is a reply to message #275550] |
Thu, 16 April 2015 10:41 |
Chris Tyler
Messages: 458
Registered: September 2013
Location: Odessa FL
Karma: 7
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Senior Member |
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Have you made sure there is no air in the line?
In start cycle they don't release that much LP so it can take a long time to bleed off.
Can you see a good blue spark when the igniter fires through the sight glass?
Does the range light /burn OK?
Have you checked the LP pressure with a manometer [~11 "WC]
Have you made sure no critters are blocking the vents outside?
76 Glenbrook
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