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Tim H.
Tim H., HVAC Professional
Category: HVAC
Satisfied Customers: 3971
Experience:  Experienced in all aspects of HVAC, both residential and commercial.
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My old carrier unit 38YRA series, has an unusual problem.

Customer Question

My old carrier unit 38YRA series, has an unusual problem. Whenever it is turned on the indoor unit has relay that cuts in and out. Sort of like the blower won't run, however if you switch the thermostat to Fan on, the blower works fine. While this is happening the outside unit never tries to turn on at all.
JA: Just to clarify, do you think this is a larger HVAC problem, or something specific to the thermostat?
Customer: Well that's the thing. I believe that it is related to either the fan relay printed circuit board in the inside unit or the thermostat. It's a weird problem that I've never seen before. The compressor and refrigerant levels are fine as they were checked out a week ago, by a local company.
JA: Do you plan on doing the work yourself?
Customer: Yes, if it is unrelated to refrigerant I can do most common repairs myself , ie capacitor/contactor replacements etc. Ok here is one more thing to let the tech know. When it gets into this mode the sound of a relay cuttting in and out does not stop even when I put the thermostat in the "off" mode. The only way to make it stop is to turn off the main circuit breaker for the unit.
Submitted: 4 months ago.
Category: HVAC
Expert:  Tim H. replied 4 months ago.

Hi, I'm Tim and I'm an HVAC expert here to assist you with your questions. Please provide all information I request as it makes it more difficult to troubleshoot something when I'm not there onsite. Essentially, you become my eyes and ears. Thanks for the opportunity to help. At the end of our dialog, you will have a chance to rate my service, but please wait until we are finished and you're satisfied you have all the information you need. Please be patient as many times we work with several customers at once.

If the unit has a board on the indoor furnace, it could be a bad board. Check across C or COM to G where the thermostat wires attach on the board. Do you have a constant 24 volts when cooling is called for?

Customer: replied 4 months ago.
That is what I am going to check when I get home. I was going to do a direct measurement & comparison to my identical downstairs unit. Unfortunately I won't be home for another hour so I'll let you know what I find in a bit.
Expert:  Tim H. replied 4 months ago.

OK, sounds good.

Customer: replied 4 months ago.
Tim, Sorry it took so long to get back to you. I believe I have found the problem. It appears to be board that controls the blower. It has a timer chip that is powered by 18 volts DC (the regulator two diodes & 2 caps) is built into the board. The regulator appears to have failed. I will verify & repair the board tomorrow- (I'm an electronic tech). If this is the only issue I should be good. Otherwise I may check in again. This would explain the weird issues. The board is Carrier part number CES0130003-00
Expert:  Tim H. replied 4 months ago.

I kind of thought it might be a board problem.

Expert:  Tim H. replied 4 months ago.

Let me know if you have additional questions. Otherwise, good luck! Thanks for using Just Answer and please don't forget to rate my service as that's how experts get paid (thanks in advance for any bonus left). Otherwise experts work at their own time and expense. Even though the Just Answer site has your money on deposit, it does not get transferred to me until you (positively) rate my service. Feel free to post back with any more questions. Remember, you can rate question at any point and still ask more questions (related to the same thing) later on. Experts prefer if you rate question at the end of our first chat.

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