H.V.A.C Techs, Anyone want to help a guy out with his old garage furnace?

Frankenytro

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Hey guys and gals,

I am having an issue with my garage furnace that I would love to have rectified but I am in a bit over my head. I am tech savvy and do own a meter and all diag equipment for automotive/heavy duty repair so I am not a total noob (you can still call me one though) lol.

What I have is an old ITT Grinnell EXCELLO shop furnace that is having a hard time running the fan long enough. I can hear the thermostat tell the burner to ignite and then the burner does ignite and start to burn which will continue for a very long time. This could be 10-15 minutes probably. During this period of time the fan will cut in periodically for approximately 15-20 seconds and then cut out while the burner continues to run. This will happen again in 3-4-5 minutes but again the burner never stops (due to the thermostat commanding for heat in my thought process) and the cycle continues until the temperature is met and the thermostat is satisfied.

There are two snap disks on the unit, one has 3 wires and has no visible temp stamp on it, the other has 4 wires (one of the 4 is piggy backed on to the first switch) and has 135*F stamped onto it.

I called in and talked to a gentleman who was older and very experienced at Sinclair Supply and he told me to come in and he would set me up with some components to install to rectify the issues. He has sold me a fixed setting snap disk fan control with 130*F close and 115*F open (P/N L36-111) as well as a fan / heat sequencer (P/N 24A34-29).

I am looking at these parts and I am at a loss as to how to install them.

Are any of you fine folks possibly able and willing to spend some time talking a guy through this repair? I know there’s still life left in this furnace and I am trying to not have to replace it all together, but it is shockingly hard to find techs willing to come and just repair and ancient shop furnace lol.

Thank you all in advance!
 

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JMCX

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Is there a wiring diagram on the back of the cover?
 

Frankenytro

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Sadly the cover is not attached to the furnace this is how it looked when I bought the place.
 

Frankenytro

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My problem is not knowing how to wire in with the gas valve and such as I am not sure what any of that end does
 

JMCX

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Try just changing the simple switch. The fan control. It only has two sides.
 

Frankenytro

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That’s not a bad idea. I will just change the switch out tonight.

I am also trying to understand what the second piece is as the guy from Sinclair was saying that I really should have both installed which would have 3 switches in place.

Either way, I will throw the new 2 pole switch in and see how it goes I suppose. Parts till it starts lol.
 

moyiesledhead

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One of them (lower temp) is the fan switch. That's your likely problem. The other is the high limit, shuts off the gas valve if heat exchanger temp gets too high. From the pic I cant tell you which is which. They're both old, so just direct replace them both.
 

Frankenytro

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Thanks for the help guys.

I will try to change to 2 pole switch tomorrow. I forgot to grab a piggy back spade terminal from the shop today.

The 4 pole switch sounds like it is less than desirable to find which is why the gentleman at Sinclair Supply wanted to implement this 3 switch set up. Or that’s what I took from the conversation lol.

I would have been happy to just purchase both new switches and make her run like new again. Unfortunately I have sadly found that it just isn’t the case for likely 40-50 year old shop furnaces.
 
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