Bad draft inducer motor?

Problems related to residential installations.

Bad draft inducer motor?

Postby hvachvac » Sun Dec 09, 2012 9:43 am

Hey guys. We just bought this house and the furnace runs differently than I am used to. From what I've read the draft inducer motor should run for about 30 sec. before the burners ignite? Mine is on for about 2-3 and then the furnace kicks on. but after a cycle and the burners shut off. the inducer motor will repeatedly kick on for about 3 sec. and shut off. It does this 10-20 times after every cycle. Does this sound right? Thanks for the help.
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- Bad draft inducer *

Postby Freon » Sun Dec 09, 2012 12:34 pm

When the burners shut off after the thermostat set temperature is satisfied, then the entire furnace should shut off except the main blower may continue to run for 30 more seconds. The behavior of the inducer isn't right.

The first question is are you certain the thermostat set temperature has been reached when the burners shut off?
If the answer is yes, then either the thermostat may be sending heat requests intermittently (not likely) or the control board is flaky. You can try the following test to determine a bad thermostat.

Turn off the power to the furnace. At the furnace control board disconnect the W wire and tape the bare end. Now with a short piece of insulated wire you're going to jumper the W and R terminals. First, you can connect one end of the wire to the W and then you will touch the other end to the R.

Now with the furnace power on, touch the jumper wire to the R terminal. There may be a small spark but hold the wire firmly... it's only 25 volts. The furnace will start as it always has. Let the furnace run and after the burners have been on for a minute and all seems stable, remove the wire you've been holding from the R terminal. The furnace will now shut off. If the inducer still behaves in that previously odd manner, carefully check the control board for any signs of heat damage or cold solder joints.

Be sure to turn off the furnace before reconnecting the W wire from the thermostat to the control board.
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