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Old 01-09-2010, 04:08 PM   #1
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Need help with thermocouple replacement on MC furnace


Typical problem, pilot light burns as long as I hold the valve's "knob" down, but no matter how long I hold it down the pilot light goes out soon as I release it. Sounds like the thermocouple to me. Just to be sure, I did replace the electrical switch that routes 120V power to the furnace, thinking perhaps the control valve had no power, so that ought to be OK.

It's a Magic Chef, Model G82-75D2C3.5-10

Serial No. A25216F9B (might be A25216F98, I can't see the last letter/digit very well).

Stamping # 31268D11

Input 75,000 BTU/bonnet 60,000 BTU

I'd sure be grateful if anyone can tell me how to get that thermocouple out. The unit is a horizontal central furnace sitting on the attic floor. There are two "vents", one on each side of the furnace, to allow in fresh air for the combustion chamber, but neither is large enough to get both hands in. I can get one hand in and can touch and actually wiggle the top of the thermocouple, right next to the pilot light's "hood", but can't seem to get it loose.

Any takers? It looks to me like the entire cabinet has to be disassembled to gain access to the thermocouple, I can't imagine ANY self-respecting company, much less Magic Chef, would design a furnace that required that level of effort to replace a such frequently replaced part.

Google was no help .....

There must be something I'm overlooking......please help!

I can post photos if that will help any......

Thanks SO MUCH for any assistance you can offer!!!!

Dugly

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Old 01-09-2010, 06:56 PM   #2
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Need help with thermocouple replacement on MC furnace


Pics would help

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Old 01-09-2010, 07:13 PM   #3
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Need help with thermocouple replacement on MC furnace


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Pics would help
Thanks, John.....check back tomorrow, I need batteries for the camera. I'll get the photos up in the morning.

Dugly
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Old 01-09-2010, 07:46 PM   #4
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Need help with thermocouple replacement on MC furnace


If I am picturing your furnace right, that whole burner tray slides back and comes out through the opening. It requires being disconnected from the gas pipe and the wires on the valve need disconnected. You also need to take the screws out on both sides of the tray.
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Old 01-11-2010, 04:34 PM   #5
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Need help with thermocouple replacement on MC furnace


Quote:
Originally Posted by JohnH1 View Post
Pics would help
Hope these will suffice:

Here's a photo of the front of the unit (all grilles/guards have been removed so that I could see inside--that was before I gave up and asked for advice):



Here's the end of the gas manifold on the "front" of the cabinet, capped off b/c the control valve is on the rear of the furnace:



Here is a shot of the rear of the stove, you can see where the gas line for the pilot light and the thermocouple tube go in (again, the "grille" is removed):



In this photo you can sort of see the hood over the pilot light and the tip of the thermocouple to it's right:



Quote:
Originally Posted by SKIP4661 View Post
If I am picturing your furnace right, that whole burner tray slides back and comes out through the opening. It requires being disconnected from the gas pipe and the wires on the valve need disconnected. You also need to take the screws out on both sides of the tray.
OK, Skip, I think I now see what you are talking about. I didn't notice these 'till I was up there taking photos, but here are two shots of what I think are the brackets that hold the tray inside the body of the furnace, one on the front and one on the back:





If you are correct, I suspect you have not only solved my problem with access, but provided me with a way to get in there and clean out a couple of decades worth of crapola that is all over the bottom of the cabinet. The thermocouple is closer to the rear of the stove, but if I can get this whole tray out the front it would make it easier to get in there with a vacuum to clean out the cabinet. I know that would require removing the gas valve from the heater's manifold, but as long as I am careful to get it back on right and check the junctions for leaks with some soapy water once I've pressured up the system I ought to be OK, right? It would have been so much easier if the relays/gas valve had just been installed on the front of the cabinet, but oh, noooooo.....

I hope these have been of some assistance, if not please let me know what else you want to see and I'll crawl back up there and take more photos.

Oh, yeah, other than cleaning out all that crap on the bottom of the cabinet, is there anything else I ought to be doing to be proactive--paint up rusty parts, whatever.....I'll do pretty much anything that I can do to help this furnace last a while longer.

I really appreciate all your help, fellows.....I was ready to give up and call the repair shop, and the last time I did that the bill was over $150 for about half an hour's work......that just me if I can do it for myself!!

Thanks, again!

Dugly
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Old 10-09-2010, 01:56 PM   #6
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Need help with thermocouple replacement on MC furnace


I just started trying to replace my thermocouple as well. For the sake of the search engines I thought I would mention that the pics here and advice appear to apply to at least one other model of Magic chef furnace

G8a100DC48-10

There might be others - the design of the unit looks almost identical to mine.

I'll see about taking some pictures of the swap in case it helps anyone else. It would be really nice if you could find an owner's manual for these things!!


P
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Old 03-04-2011, 01:28 PM   #7
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Need help with thermocouple replacement on MC furnace


After 3 hours of trying to get to my pilot & thermocouple, I gave up & called a repairman, but then found your pictures & saw it looked very similar to my furnace--fortunately the repairman did not show up, so I investigated more and found your posting.
Thank you sooooo much for your pictures. I too tried to get to my blind thermocouple (to an old Johnson Corp furnace) by attacking all the screws I could find on the panels & still could not see the @#$% thing. Then I found this site & saw that you probably found the solution, but I wasn't sure it was successful until I was able to pull my burner assembly out to expose the secretive pilot & thermocouple. The solution was to simply remove the front & back grilles (vents), then remove the 1 ft. long metal angle iron bracket (shown at the bottom of your 1st pic) that holds down the entire burner assembly, and then the entire assembly slid out so everything was accessible. No wires or lines to disconnect. Most of my time was involved in putting all the screws back on the panels that did not need to be removed. Replacing the thermocouple was a snap!!!
In the photo below, the angle iron bracket is marked by the small elipse. The burner assembly is marked by the larger elipse. All of this is behind the grille/vents on the front & back of the furnace.
I hope this helps someone else who has an old furnace and wants to save a couple hundred dollars. Thermocouple costs between $10 to $15 and can be found at Home Depot or tool supply company (I used Grainger in Houston TX).
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Need help with thermocouple replacement on MC furnace-furnace.jpg  

Last edited by gvalka; 03-04-2011 at 02:03 PM.
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Old 03-04-2011, 05:56 PM   #8
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Need help with thermocouple replacement on MC furnace


Many pilot electromagnets in gas valves can get a bit sticky. After you've lit the pilot, kept it burning for at least a minute, try taking a pair of pliers and wrap it a few times on the metal of the gas valve the way you'd normally knock on someones front door while you are still pushing down on the gas valve control. If it goes out when you let off the gas valve control then do it all again right away. If it goes out a second time then its back to repacing the thermocoupler again.
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Old 01-13-2012, 07:24 PM   #9
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Need help with thermocouple replacement on MC furnace


GREAT conversation guys. Thanks for the help. My Magic Chef G83-100D2c3.5-5 furnace pilot light would not stay lit. After seeing the photos and reading the posts, I was ready to disassemble the existing thermocoupler and buy and install a new one. It made sense about the alignment of the thermocoupler and potential debris from possible rust falling into the pilot, so, for one last try with this new information, I took off the grill, tried to lightly squeeze the pilot light and coupler closer together and then lightly tapped and ran my fingers all around the pilot light. I tried to light it again and noticed the flame was brighter this time as I held the pilot button for 30 seconds...knowing it would work this time, and it did. I'mm thinking that rust may have dropped into the pilot from the rusting metal above. My tapping may have knocked it out or at least reconfigured it such to allow more gas to exit and therefore burn.

If the thermocoupler goes out, however, I'll be ready to replace it.

Thanks!!

Steve

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