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enter image description hereenter image description hereenter image description hereenter image description hereenter image description hereenter image description hereTwo weeks ago my condenser fan started overheating after 15 to 30 minutes of runtime. Seeing as capacitors are cheap I replace the capacitor first. The problem persisted so I ordered a new fan motor. Same specs 1/4hp 825rpm 2amp from Novac. The problem still persists. Thinking voltage through the contactor may be the issue I replaced the contactor as well. Problem still persists. Cleaned coils cleaned all electrical connections. I'm at a loss could a low charge cause overheating of the coils and in turn cause the motor to overheat. Photos A/C unit https://imgur.com/a/ZcImE4C

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    What is the voltage to the motor? Over or under volt can make it overworked and overheat. How did you determine it is overheating?
    – RMDman
    Commented Jul 23, 2023 at 16:06
  • Are these motors 120 V or 240 V/ Commented Jul 23, 2023 at 16:17
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    241V reading at the black and white wires going to the fan. Figured out it's overheating because when it shuts of the fan motor is to hot to touch.
    – Richard
    Commented Jul 23, 2023 at 16:17
  • 208-230V is what the tag reads
    – Richard
    Commented Jul 23, 2023 at 16:18
  • Also just remembered when if cuts out the contactor will not disengage until I flip the breaker even if it's off at the thermostat the contactor attempts to stay engaged until power is cut completely. This only happens when the fan shuts down though. Don't know if it's important but it seems odd.
    – Richard
    Commented Jul 23, 2023 at 17:59

2 Answers 2

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Too hot to touch may be perfectly normal. Quoting from drivesandautomation.co.uk:

Heat kills, and the old standard of using your hand to judge the temperature of a motor and if it was over heating no longer applies. NEMA Insulation Classes do away with guessing, and give the motor manufacturer a defined framework to operate in. The Surface temperature of the motor is typically 30°C lower than it is at the windings. So if we look at a Class F insulated motor which will be happy running at 155°C and then subtract 30°C, we get a surface temperature of 125°C. This doesn't necessarily mean it is running too hot or operating improperly (by the way, we strongly advise against touching anything that is 125°C). To put it simply, today's motors can simply be too hot to handle, even when all is working as it should be.

Motor winding insulation max temperature ratings carry NEMA designations. These ratings are defined as:

Class: A 105 Degrees C

Class: B 130 Degrees C

Class: F 155 Degrees C

Class: H 180 Degrees C

Continue reading the article.

So if your motor has Class F insulation, which is commonplace for A/C condenser fan motors, the outer case could actually sizzle when you touch it with a wet finger, and it would still be within the normal working temperature range.

You can measure the temperature of the case with a non-contact IR thermometer. You generally have to point one of those at a painted surface because a bare metal surface gives a false reading.

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  • OK good info, so if not heat then what is shutting the motor down. I don't have any kind of thermometer to measure the temp but it will turn back on after it cools down.
    – Richard
    Commented Jul 23, 2023 at 17:56
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    @Richard Neither your original post nor your comments to answer the queries before I provided this answer mentioned that something is shutting down the fan motor while the compressor is still running and with the thermostat not calling for cooling. That's what you're saying now, right? All you said before is that the motor feels hot after it turns off. Provide a schematic for your A/C to further the diagnosis.
    – MTA
    Commented Jul 23, 2023 at 19:08
  • Yes that's what I'm saying sorry for the misunderstanding. It's hard to provide a schematic due to all the labels being to faded to read a model name or number to find a schematic. The only thing I know for sure is that it's a Ruud split heat pump unit. If there's a way to add photos on here I could take some photos but that's the best I can do. I appreciate all the help.
    – Richard
    Commented Jul 23, 2023 at 20:58
  • @Richard To add photos, click EDIT on your question, then use the icon that looks like mountains to add photos. You can also search online for a schematic. You'll need the make and model number of your A/C. Look for a metal name plate on the unit, which should have model and serial numbers.
    – MTA
    Commented Jul 23, 2023 at 21:01
  • Added a link to photos the site wouldn't let me upload due to being to large
    – Richard
    Commented Jul 23, 2023 at 21:17
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The problem turned out to be the defrost control board. I was able to retrofit a White Rodgers Universal defrost control board and everything seems to be working fine now.

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  • Good job, thanks for the update.
    – MTA
    Commented Jul 29, 2023 at 0:54

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