Combo Furnace Issues

Problems related to residential installations.

Combo Furnace Issues

Postby ApolloX » Tue Sep 04, 2012 12:45 pm

New home owner with central air. Fan unit in the attic and two ACs outside. The problem we're having is with the furnace component in the basement, that I believe includes a fan used by the AC to circulate air.

First off, with the AC turned off on both thermostats, the furnace fan continues to operate and circulate air. Is this normal to have the furnace unit fan not controlled by the thermostats? Is there a good reason for doing so?

Second, the furnace is making a high pitch sound throughout the duct work, which to me sounds like the fan might be dying.

Finally, there is a small puddle of water around the unit which may or may not be released to fan sound. Also, the PVC pipe that vents air is full of water. I haven't lived at the house long enough to know if this kind of behavior is normal.
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- Combo Furnace Issues

Postby Freon » Tue Sep 04, 2012 1:42 pm

"First off, with the AC turned off on both thermostats, the furnace fan continues to operate and circulate air. Is this normal to have the furnace unit fan not controlled by the thermostats? "

Check the thermostat setting for FAN. Is it set to AUTO or ON? If it's set to ON, change it to AUTO. If that doesn't help you may have a fan control relay that is defective.

"Second, the furnace is making a high pitch sound throughout the duct work, which to me sounds like the fan might be dying."

It is possible the motor bearings are going bad. Only way to know is check the motor directly, once you stop it.

"Finally, there is a small puddle of water around the unit which may or may not be released to fan sound. Also, the PVC pipe that vents air is full of water. "

The symptoms are those of a clogged evaporator coil drip pan waste line. Find where that PVC pipe exits the house and using a shopvac try and suck any material out that could be preventing the water flowing from the drip pan.

Make and model number of all equipment is always helpful.
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- Combo Furnace Issues

Postby ApolloX » Tue Oct 02, 2012 5:07 pm

- I had someone come out and they replaced the motor, as they said it was definitely dying. The leaking was caused by a clogged drain pipe that has now been snaked.

The only issue that seems to randomly reappear is the blower fan always being on. It worked fine when I had a technician out in AUTO mode, but today started always being on. I even went so far as to power off the thermostat and pull out the wire green fan wire, and it was still on. Is there a wire fused somewhere or is it a function of the furnace to turn on under certain conditions, like when it is raining? It's a Ruud furnance.
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- Combo Furnace Issues

Postby ApolloX » Tue Oct 02, 2012 5:32 pm

I checked the wiring to the furnace, disconnecting the G wire directly on the furnace and it still kicks on. Based on readings on the internet, it sounds like a stuck relay?
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- Combo Furnace Issues

Postby ApolloX » Tue Oct 02, 2012 6:17 pm

The model is a Ruud UGRA-12ERAJS. On oddity is I can't seem to find the relay. There's a fan control circuit board behind a metal cover. Is the circuit board the equivalent of a relay switch for this model?
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- Combo Furnace Issues

Postby Freon » Wed Oct 03, 2012 3:50 pm

The relay may be mounted to the control board. Follow the wires from the motor back to where they connect to something... most likely the control board. That will tell you the realy is integrated into the board. You can try and replace just the relay but it may be more cost effective to get a new board.
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- Combo Furnace Issues

Postby ApolloX » Wed Oct 03, 2012 4:02 pm

There's no single wire to the circuit board, it uses a plug. Here's a -

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Put "e c r a t e r . c o m" in the **** above without spaces.
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- Combo Furnace Issues

Postby Freon » Tue Oct 09, 2012 2:42 pm

If all the blower motor wires plug directly to a plug mounted on the control board then I would say the relay is on that board and you need a new board.
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- Combo Furnace Issues

Postby ApolloX » Tue Oct 09, 2012 2:50 pm

After further testing, the board is definitely not working. New board it is. Wish the relay was separate, that would have been easier (and cheaper) to change.
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