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Scott
Scott, HVAC Technician
Category: HVAC
Satisfied Customers: 398
Experience:  30 yrs. experience as self-employed HVAC Service Technician. Universal EPA Certification, NATE Certified, Trane Service One, ACCA ACE Certified.
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I have a Ruud ugdg-12earjr furnace. The unit is not heating

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I have a Ruud ugdg-12earjr furnace. The unit is not heating (the ignition cycle does not occur). The blower is running continually as though the burners are running and will only shutoff if the power to the furnace is shut off (shutting the thermostat off does not have any effect). I read some information that air limit switch might be defective so I replaced it. This did not solve the problem. I am wondering what else might be the problem.

gurutech67 :

Does the Furnace heat at all?

Customer:

No. It just runs the blower as soon as power is applied

gurutech67 :

is the furnace an upflow or downflow

Customer:

I think up flow (the air filter is below the heating section)

gurutech67 :

ok the switch that u replaced was it in the middle of the furnace or in the blower section

Customer:

I guess it was the middle. It is in the compartment with the heating tubes, gas lines, and ignitor. There is also a fan in that section. The switch I replaced has 2 electrical wires connected to contacts on the switch labeled 'C' and 'NO' and a small rubber hose connected to a blower fan.

Customer:

The part number was 42-22682-02

gurutech67 :

The switch that you replaced is called the pressure switch, does the furnace you have, have a solid state circuit board in the Bottom of the furnace. also is it just the blower motor that runs constantly or is it bothe the inducer motor thats the little motor in the burner comartment run also.

gurutech67 :

is your filter dirty?

Customer:

There is a circuit board located in a metal box in the lower section of the furnance

Customer:

air filter was recently replaced

Customer:

looks clean

gurutech67 :

The Main Limit switch is located above the inducer motor it has two wires going to it but they aren't marked Com & N.O. stands for common and normally open. the purpose for this switch is to keep the furnace from over heating. There are also burner rollout switches that have a little button on them that may need to be reset.

Customer:

There is a small switch in the middle section that has 2 wires connected to it with a small red button that is sticking up

gurutech67 :

push on that button to see if it clicks

Customer:

ok

Customer:

Yes it clicked and now the blower is not running when the main power is applied

gurutech67 :

ok turn the thermostat up to see if it will run and light , by the way does your furnace vent out with plastic pipe or metal.

Customer:

I will try the thermostat and look at the connections, be right back

Customer:

The furnance is now running correctly, the ignition occurred and the burners and blower are running normally

gurutech67 :

Now just be sure it's getting as much air to it as it can get and no cold air returns are blocked, if the old filter was blocked it may have caused the switch to trip. by the way my name is Scott.

gurutech67 :

If you could give me a good rating I'd appreciate it.

Customer:

Thank you Scott! It is going to get very cold tonight (7-9 degrees) so having the heater running is great thing

Customer:

I will check the filter again, is there anything else that might cause that switch to pop?

gurutech67 :

where are you located? Im in Indiana, was the switch on the burners or on the metal back plate of furnace.

Customer:

I am in Denver. The switch was connected to the metal backplate

gurutech67 :

that is cold I hope it gets cold here soon as I own A heating Company it was the main limit so it would be only a lack of airflow that would cause it to trip. a roll out switch is a more serious problem needing a service call, but I think You'll be OK.

Customer:

Great, thank you for your help. I will definitely give you an excellent rating!

gurutech67 :

Thank You Very Much.

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