Blower fan won't shut off


Old 12-19-01, 10:35 AM
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Blower fan won't shut off

I have a 10-yr old split Trane Heat Pump (800 series). The fan on the 'inside' blower unit will not shut off, no matter what I do, short of cutting off the unit's circuit breaker. I turn the thermostat fan control to 'Auto' and it never turns off. I turn the thermostat's mode switch to 'Off' (it's either 'Off', 'Cool', or 'Heat') and the fan still runs, no matter how long I wait.

I'm thinking either the thermostat's switch has gone bad, or there's a stuck relay somewhere in the blower, or a bad contact in the outside exchanger unit. ???

The kicker is that (I think) it has just started since the we had a repair guy here last week; the unit had not been heating/cooling, and he checked out the system and said all that was wrong was that it needed about 1.5lbs of refrigerant. He said the system's capacity is about 5lbs. Anyway, it's heating much better now. I'm thinking that when he did his checkup, he did something that messed up a relay or some wiring (?). Though it's always a possibility, I doubt he did it on purpose...there are far worse things he could've done, I suppose.

I wanted to know if there's something I can check myself and avoid a $50+ service call. I'm familiar with electronics (well, I can run a multimeter ) so I can do routine checks. I'll probably test the thermostat's switch, but much beyond that and I'm following my nose...

Any help/suggestions would be appreciated. Thanks.

(p.s. I know that some would say that a constantly running blower is a good thing, but since my ductwork is in the attic, it is a big source of heat loss)
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Old 12-19-01, 01:31 PM
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Arrow Fan Switch Stuck

Hello kwpoore and Welcome to the Heating and Cooling Appliance forum and our Do-It-Yourself Web Site.

Chances are very good the fan relay switch is stuck. Try hand rapping the unit when the fan will not shut off. The hand rap should jar the contacts of the relay switch and cause them to seperate.

In this case, the fan should shut off. If so, replacement of the switch is the only solution. Be sure to wait long enough b4 rapping the unit. Well past it's normal automatic turn off time to insure it is the relay switch causing the problem.

Below are Excerpts from several of my prior posting replies which may help you to resolve the problem your describing.

Without knowing which type of heating furnace you have, it's location, brand, model, year, etc. I have to assume it's a forced warm air furnace. Forced warm air meaning it has a fan motor which distributes the warm air produced by the burners through heating ducts and out through registers in the rooms.

The fan switch turns the blower fan on when the firebox {heat exchanger} reaches a preset temperature. When the fan motor continues to run continuously long after the heater burners turn off, the most likely problem is a fan switch has become stuck in the closed position.

The fan switch {often referred to as a fan relay} has either contact points that open and close or a bimetallic strip which allows electrical current to flow to the fan motor. When the switch wears out, the fan motor will not automatically turn off.

To resolve that problem, the fan switch needs to be replaced. One method to help with verifying if the switch is defective, when the fan motor fails to turn off after the burners turn off, firmly but gently wrap the fan switch cover or a solid part of the furnace frame near the switch with your hand, lightly closed fist or backend of a screwdriver.

This action should jar the fan switches contact points or bimetallic strip enough to turn off the blower fan. If this wrap does infact turn off the fan, the fan switch is defective and needs to be replaced.

Use CAUTION around the switch when attempting any type of test and or repairs. It uses full houseline AC electrical current to function. Be sure the furnace is unplugged or the electrical current is first turned off to the furnace prior to attempting any services.

Replacement of the switch is required. Attempting to adjust the existing set temperatures will not correct the problem. Altering or adjusting the preset temperatures in an attempt to correct the above mentioned problem, may do more harm the good.

When replacing the switch install an exact OEM replacement part available at your local appliance parts store listed in the phone directory or obtain one from a heating and air conditioning supply store, which are also listed in the phone book.

Safety Reminder:
Be sure to use caution. Turn off the power supply or pull out the electrical plug from the wall socket prior to removal. Also be sure to replace the existing wires to the replacement part exactly as the are currently connected on the existing fan switch or relay.

The do-it-yourself person can do electrical tests and continuity tests on several of the parts. However, bare in mind that neither of these tests will provide proof positive the part is actually functioning correctly. Therefore, do not rely solely upon either test.

The only positive proof any part is functioning correctly, is to carefully remove the part or parts you suspect to be the potential culprit, and have the local appliance parts store person test it or check it. Appliance parts dealers carry replacement parts for all appliances and are listed in the phone book under appliances.

Read the manufacturers online web site for product information, problem solving methods, disassembly, reassembly methods, repair proceedures and instructions, pictorials and schematics, which may be available online.

Check the ARCHIVES, within this forum, for other postings on the topic of your question and the replies posted.

Regards & Good Luck
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