Blower motor runs continuously


Old 01-14-03, 08:43 PM
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Blower motor runs continuously

I have a Rheem furnace that is approx. 25-30 years old. I just replaced the blower motor, fan limit switch, transformer/fan center, gas valve and thermostat. Burners seem to work fine and come on and off according to the upper limit of the fan limit switch. Problem is the blower runs continuously even when either of the wires on the fan side of the fan limit switch are disconnected and even when the system is turned off at the thermostat. The fan setting on the thermostat is on auto and the push button on the fan limit switch is in the auto position. I must have it wired incorrectly somewhere. Below is the wire routes I have.

Fan side of fan limit switch:
Load wire connects to red fan motor wire
Line wire connects to red transformer/fan center secondary wire

Limit side of fan limit switch:
Load wire connects to gas valve
Limit wire connects to transformer/fan center along with white thermostat wire.

Second gas valve wire connects to transformer/fan center along with white A/C wire and a hard wired transformer/fan center wire.

Transformer/fan center white primary wire connects to fan motor white wire and 110 white wire.

Transformer/fan center black primary wire connects to brown transformer/fan center secondary wire and 110 black wire.

Transformer/fan center black secondary wire connects to black fan motor wire.

Green thermostat wire connects to transformer/fan center along with a hard wired transformer wire.

Yellow thermostat wire connects to red A/C wire at the transformer/fan center.

Red thermostat connects to transformer/fan center.

Can you help me find my mistake?
Old 01-15-03, 05:06 AM
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Your post is rather confusing, but I would say your problem lies in the fan center primary(110v) wiring. The fan center relay has a normally open and a normally closed set of contacts. Most fan centers have three wires coming off this relay. One is power in, the normally closed side goes to the fan/limit switch then the low speed blower wire and the normally open goes to the high speed blower wire. Hope this helps.
Old 01-15-03, 07:50 PM
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I can't tell whether you have the wiring correct or not but there are two things that come to mind. If you take the low voltage wire off of the G terminal and the blower doesn't stop, I think you have a line voltage problem. As the previous reply stated, the fan relay has a normally open and a normally closed set of contacts. The wire color codes aren't always the same between brands so you will have to check closely. The low voltage wiring designations are standard. R is 24 volt power. W is heat Y is compressor C is 24 volt common and G is fan. A jumper from R to G should pull in the fan relay. It will make a loud click so you can verify that. Lift the wire from the G terminal first so you know it is not already pulled in. There is more than one way to wire a multi speed fan and the one I prefer uses both poles of the blower relay. After the power leaves the fan control (triggered by plenum temp) it passes through the normally closed contacts of the fan relay on its way to the fan motor medium speed. If the a/c was activated while the plenum was hot, the blower relay would activate high speed while disconnecting the power from the fan control. This prevents the one in 1000 chance that you power 2 speeds of the fan motor at once which is a no-no.

Yours does not sound like it is wired this way. If you look on the back of the fan relay, you will see the diagram of what each line voltage terminal is for.

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