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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8274
Experience:  Furnace, A/C and heat pump specialist.
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What causes my furnace blower to run in the off position?

Customer Question

What causes my furnace blower to run in the off position?
Submitted: 1 year ago.
Category: HVAC
Expert:  airheatman replied 1 year ago.

Usually either an open limit switch or a bad fan relay. Does heat work normally other than fan not shutting off?

Customer: replied 1 year ago.
Heat will not come on, blower just runs when power switch is turned on.
Expert:  airheatman replied 1 year ago.

You most likely have a limit open. Can you take a picture of the wiring and furnace components and post it here using the paperclip icon? And do you have a meter for troubleshooting?

Customer: replied 1 year ago.
I have attached pictures and I do have a volt ohm test meter.
Expert:  airheatman replied 1 year ago.

Ok the furnace is going to have between 2 and 4 limits .WE need to locate them .Then unplug and ohm each one out to see if ne is open.

Main limit is in center of vestibule behind gas valve (about the size of a credit card with 2 terminals. The others will be smaller and may have a button in center to push in and reset. Follow the wires from the limits we can see easily all the way to board to locate any others in circuit.

Customer: replied 1 year ago.
There are 3 in the entire circuit and all test to be closed or zero ohms.
Expert:  airheatman replied 1 year ago.

Are yu getting a flash code on the board? If so, how many blinks between pausing?

Customer: replied 1 year ago.
Four flashes, sticker says rollout or limit switch open.
Expert:  airheatman replied 1 year ago.

Sounds like we may have a bad board not reading the limit circuit closed if we have continuity all the way through the circuit and connects are good at board.

Customer: replied 1 year ago.
What can I do now, replace it?
Expert:  airheatman replied 1 year ago.

That would be my next step if I have proved there is not an open limit.If you see part number on board I can try to help you locate one if you nee me to.

Customer: replied 1 year ago.
The part number seems to be ST9160B1076
Under that number was also 20430801
Expert:  airheatman replied 1 year ago.

The ST9160B1076 is a good number

You may also Google it and find a better price.

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