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gotoman for ac
gotoman for ac, HVAC Technician
Category: HVAC
Satisfied Customers: 5205
Experience:  51 years of experience install design and repair of all makes and models of AC
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Tempstar DC90 Model # NUGMO75EGB1 My furnace stopped heating.

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Tempstar DC90 Model # XXXXX

My furnace stopped heating. It was working fine and then at the end of its normal cycle, after it purged any remaining heat, it continued to run without heat. I turned the switch on the thermostat to off, but it still blew cold air. I had to then turn off the switch located on the furnace itself. Any ideas? Perhaps a sensor or solenoid?

Do you have doagnostic lights on your furnace? It should be in blower compartment. You will see LED lights count flashes and look on chart it willl us problem area. Check this and while you are looking get me gas valve model number please. Rus

Customer: replied 7 years ago.
I far as I can tell I have no diagnostic lights. I'm no expert, but if I understand your request the blower compartment is accessed by removing the lower panel. Am I right? I see a main circuit-board, but no lights. But.. This could be because I have turned the power off because it keeps running.

The gas-valve model no. is SV9500M 2674.
Let check limot and rollout switches. Look near burner. Just above is a limit switch. It is square and has two wires coming out of it. Take off wires and put them together and retry furnace. Also check any rollout switches to see if they need reset. They are located on top of burner. They are about 1 inch round and has a button in the middle. Check your filters also to make sure they are clean. I will pull manual on your furnace. Rus
Customer: replied 7 years ago.
The burner (where ignition and flame is visible) is located at the top of my furnace. There are no switches above it. Just underneath it however, there is a square switch with two wires coming out. I took off the wires, put them together and turned on the furnace but nothing changes. I found the rollout switch on the right side of the burner. There is something like a button between the two connected wires. I tried to push the button (not very hard) but it didn't move. The filter is about 2 weeks old and in great condition.

Whar happens whe you kill power to furnace and restart it. Give me the sequence. Rus

Customer: replied 7 years ago.
That's just the strange part of this. I turn the power back on and the blower kicks in immediately and the the exhaust blower. Thsi is in exact reverse of its normal sequence.

Well just for posteritiy's sake, I went back downstairs to confirm what I just told you regarding the sequence to be sure before I sent my response. I turned the power on and now it works. It followed its proper sequence and ignited and is now blowing out heat. Can you tell me what might be causing this? It now seems evident that it has something to do with the wires and or switches you had me inspect.
Possible rollout switch may have needed reset. I would pull and clean that limit switch. There is a disk on the end of two probes when you take it loose. There is also a flame rod that proves flame inserted into burner. Use a piece of sand paper and clean this and you will be alright. Rus If you are satisfied with my answer please press accept. Good feedback is always welcome.
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Customer: replied 7 years ago.
Well, before I worked with you on this I had no heat and now I do. Thanks a million!!
Just keep in mind the things we checked and ou will be fine. At least it is not a 250.00 gas valve. Rus