reasons blower fails to low

What should be the first things to check when a blower randomly fails to low speed after working properly? It's a TUD080R9V4k4 connected to rxco36s3hpdo and 4ttx4036a1000aa. Thanks for any ideas.
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Rald wrote:

Have you checked with your American Standard wholeseller?
Is the control wiring loose?
--
Moe Jones
HVAC Service Technician
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Hmm that is good question what you are saying it start to run ok but then on it's slows down to the low speed: does it remain running at low speed or does it shut down after while and how long does it take before it slows down, it is possible that all it needs is some lubrication or on other hand it could have shorts in winnings or running capacitor could be going bad (opening or shorting) there is several possibilities which only tech. can diagnosed the problem at your equipment sight Tony

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I agree with everything Tony said......
Wait..... What did he say?
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Check the yellow pages for your nearest professional dealer. Bubba
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Welcome, First a couple of questions. Have you posted here before, don't recognize the name? Are you in the HVAC trade, ability level? I don't have any idea of your experience or skill level.
Joseph

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If you are a technician, and not sure what to look for, I'd suggest a little more studying is in your future.
Zyp

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I apologize for not leaving enough detail or background for those who tried to take a stab at this one. I am not in the hvac trade, but thought there might be a simple solution like check the wiring, try a different 2-stage thermostat, or perhaps a known issue with the handler model. If there are no possible simple things I can try, I will of course be asking an hvac tech to stop by. The blower dropped to low speed several evening ago and has not left low speed despite the high outdoor temperatures of the last couple days. The little bit of air coming out the supply vent is still very cold.
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Bubba, whatcha think... is a new stat in order? :-)
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You have a 80% AFUE, 2-stage, Variable speed DC motor furnace that is not ramping up and staying in low speed. Was there any lighting lately around the house?

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