Furnace Expertise Help please!

Problems related to residential installations.

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Furnace Expertise Help please!

Post by jonathans » Thu Oct 03, 2013 5:50 pm

Our furnace is not working, to be honest we are pretty low on income right now and are trying to fix it ourselves... so any help would be greatly appreciated. Heres what we know or think we know. (My father added a few things that may be necessary or unnecessary, please forgive me if the information is not correct)

Rheem Imperial 80 Plus Furnace

The furnace has been set up to run the fan constantly at low speed, circulates the air in the house all the time. When the heat/cooling is active a separate exhaust fan in the exhaust pipe will come on and clean out any gas in the pipe, then the furnace fan will increase speed to move the air around the house, then again the exhaust fan will do its thing and the furnace fan will fall back to low speed ending the cycle.

Furnace was not working in air conditioning mode then stopped working. We did not notice when this happened, only discovered it when it got hot and tried to put the air conditioning on.

The furnace motor continued to run, tried to switch to heat with the same results, no heat but the fan continued to run.

There is a fan motor run capacitor (10 microfarad 370 volts plus-minus 5%) that starts the motor and I thought it might also control the fan speed changes when the heat/cooling actually came on. I replaced the capacitor with a 10 microfarad 440 volts plus-minus 5% (should be ok as a replacement?) but it made no difference at all.

TDLR Fan still runs but heat/cool wont work! Help!

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- Furnace Expertise Help please!

Post by Freon » Sun Oct 06, 2013 4:08 pm

Can you tell us how the furnace was set up to run the fan constantly? Was it using the thermostat or a DIP switch in the furnace control board.

You need to have the furnace back to factory default settings before we can really help you. The fan setting to always on adds a complication.

Also when you call for heat, the small blower (draft inducer) starts, then there should be either a spark ignition or a hot surface ignitor (it glows white hot) that starts and then the gas valve should open and a burner flame occur. In this sequence, where does your furnace stop?

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