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I believe that the fan relay on my furnace controller is

stuck closed. What can...
I believe that the fan relay on my furnace controller is stuck closed. What can I do to confirm that, and is it reasonable to believe that it will open if I tap it?
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Answered in 2 minutes by:
9/23/2017
Rick
Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 22,547
Experience: 40+ yrs. experience as a licensed oil & gas technician.
Verified

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. If my initial response doesn’t answer your question then let me know and we can continue our conversation.

If you disconnected the thermostat leads at the furnace and the furnace is not in an open limit circuit condition then you probably do have a stuck fan relay. Tapping on the relay won't necessarily free it up.

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Customer reply replied 2 months ago
What is the next step?

Replace the relay

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Customer reply replied 2 months ago
I believe this is the manual: https://www.manualslib.com/manual/832373/American-Standard-Ud-Series.html?page=56#manualI have not been able to determine which relay it is. Is that something that you can help me with?
Customer reply replied 2 months ago
Or should I replace the board?

Give me a few to review the manual.

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The manual shows an ECM motor. This muddies the water. Do you have an ECM motor on your unit?

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Customer reply replied 2 months ago
I don't know - how can I tell?

Refer to page 19 in the manual. It shows an eight pin molex connector on the fan control board which also has the thermostat terminals strip.

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Customer reply replied 2 months ago
I see only text on page 19. It does mention K3 turning on the ECM...
Customer reply replied 2 months ago
OK, was looking at the site, rather than the manual page number. Yes, I see the diagram.
Customer reply replied 2 months ago
the 8 pin molex connector

Ok, now see i you have the same thing on your unit

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Customer reply replied 2 months ago
mine has the daughter board, if that's what you mean.

Ok then if your unit has the same board you have an ECM motor. Diagnosing an ECM motor issue is not a DIY project.

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Customer reply replied 2 months ago
Hmmm, so I should give up and call a professional?

Given the cost of the components invloved (an ECM control is sevral hundred minimum) and the expertise invleved you're better off leaving this to a pro.

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Customer reply replied 2 months ago
Why suspect the motor? Why not suspect that the fan relay is stuck, and the motor is OK?

ECM motors are a different animal. The fan controller is what controls the fan.

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Customer reply replied 2 months ago
You are certain that the motor has a problem?

That's what it looks like from here based on what you're telling me.

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Customer reply replied 2 months ago
If K3 is the fan relay, perhaps I should just replace it - or just pull it off the board to see if the fan stops. What do you think Rick?

You can't replace a relay on the board.

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Customer reply replied 2 months ago
Why not? Or I could replace the board. I think it's ~$160. It would be a shotgun approach, but hiring a pro could be $550+, no?

You're just thowing parts at it. A diagnostic by a pro is typically around $100.

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Customer reply replied 2 months ago
How do I find someone I can trust? Do you know vendors in the Boston area?

I can't make a referral. Try a referral service like HomeAdviser.com. There is no charge to you for their service. Specify your furnace brand in your service request

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Customer reply replied 2 months ago
Thank you for your help Rick!
Customer reply replied 2 months ago
Have a great day!

You're welcome

Rick
Rick, HVAC Supervisor
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Satisfied Customers: 22,547
Experience: 40+ yrs. experience as a licensed oil & gas technician.
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