blower fan won't cut off


Old 01-08-00, 09:04 PM
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We had a hvac (gas furnace) system installed to heat and cool our newly finished bonus room. When we installed the programmable thermostat and turned on the system's power, the fan came on and would not cut off. Adjusting the temperature, turn the fan switch on the thermastat to off or auto, even cutting the temperature control on the thermastat to off did not stop the fan. Only cutting the power to the unit works. How do we fix this??
Old 01-08-00, 11:08 PM
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Hello randmlewis:

I gather from your discription of this problem, that all was okay prior to installing the newer thermostat. <T-Stat>

Therefore, recheck those wiring connections behind the T-Stat. Refer to the instruction manual and also the back of the plate.

Notice on the backside of the plate the connection screws have tiny letters to indicate the color wire that should get connected there.

If the wires are connected correctly according to the colors, try these tricks.

Remove the T-Stat. Now there should be nothing but wires coming out of the wall. Plug in the furnace. If the fan comes on see #4 below.

Reinstall the old T-Stat and see if it corrects the problem. If so, check the wiring on the new T-Stat.

Re-install that newer T-Stat exactly as you had it and install the wall plug. If the fan blower turns on again, remove the furnaces front cover <assuming here that it's an upright installed in a closet> an look for a metal box about the size of a double electric wall plug box.

<It should be covered with a flat galvanized cover, with two or four screws, one in each corner.>

When you find that fan switch box, gently hit it with your hand clasped in a fist using the opposite side from the thumb. One good rap should stop the fan.

If so, the fan switch is sticking and will need to be replaced. If not, it's the wiring on the T-Stat.

Replacing a fan switch:

To remove the fan switch, unplug the heater FIRST! <Be aware that's full wall current behind that cover!> Now remove the cover and mark all the wires and there locations.

<TIP: Use masking tape around each wire and leave a tape tail to write on where the wire goes.>

Now remove the fan switch, head on over to your local heating or most any appliance parts store and buy a replacement.

Re-install the new fan switch exactly as you found and removed the defective one. Attach all wires <usually two> and double check everything to be positive it is all correctly installed as prior then close the box back up with the cover.

Install the furnaces wall plug and the fan should not be on. Test it for one cycle by turning on the heater at the T-Stat, set it up one or two degress and wait till it automatically cycles itself off.

Good Luck

TomBartco Enterprises.
Trade:Natural Gas Energy Consultant & Technician.
Appliance Service & Repairs Rep.
Vocation:Saw & Tool Sharpening and Small Engine Repairs.
Accurate Power Equipment Company.

Personal Quote: "Drive Safely. The Life You Save,
May Be Your Own."

Old 01-09-00, 09:27 AM
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Thanks for the info -- we'll try it. (By the way, the programmable thermostat is the first thermostat on this unit, not a replacement, so the problem has been there from the start.) Just to make sure we've got it right, which wire is RH and which is RC? We have a bright red wire and a brownish red one. (We also have a blue wire which is not connected at either end.) Thanks for your help!

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