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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8260
Experience:  Furnace, A/C and heat pump specialist.
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My outside compressor fan it's not running. Sound like the

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My outside compressor fan it's not running. Sound like the compressor itself is making a humming noise, but that is all.
Any ideas?

Most likely a bad capacitor. Do you have a multi meter and a capacitor tester to troubleshoot?

Sometimes when a capacitor is bad it will actually swell up.although even if not swollen it could still be bad. Can you look in outdoor unit and see if it is swollen or leaking?

Customer: replied 10 months ago.

I changed the capacitor.. It still not working. They tested the old capacitor and it was good. But still I installed a new one.

Any ideas?

WE could have a number of issues and I will be happy to help you determine exactly what is wrong.

We would need a meter to troubleshoot. If you have a meter let me know .If not you can get an inexpensive one at Walmart for about 15 bucks if you would like to troubleshoot and I would be happy to guide you.

Customer: replied 10 months ago.

yes .. I have a multimeter

Excellent. Give me model on outdoor unit to my intsuctions are specific. Then lets go to the outdoor unit contactor. WE will first turn to call for cool and see if we get 24 at coil on contactor, the check for 230v in and out of contactor as shown below.

Customer: replied 10 months ago.

model # is FX4CNF024 made by carrier

That is model on air handler. Outdo0r will be something like 25hbc025 or similar of it is also Carrier

Customer: replied 10 months ago.


OK remove the corner panel and you will see the contactor mentioned.Let me know if we have 24vbetween coil and 230 between in and out terminals with thermostat calling for ac.

Customer: replied 10 months ago.

I was getting 240V on the side from the upper 2 wires (numbered 21 and 23) while the thermostat showed "cool on". I could not trace the 24 Volts on the smaller cables however, I think my voltmeter is acting up. Also, I disconnected the 240V breaker and the 2 black wires (numbered 21 and 11) had continuity. Again, it could be my voltmeter was not reading good. I'm going to get another one and get back to you with the new readings.. Here is an image of my contactor.

Thank you

OK terminals 21 and 11 having continuity indicated that the plunger is pulled down so we should have power to both the compressor and the fan motor.

If capacitor is good, you have a bad fan motor and will need to replace it.

AS for the compressor, it will start at first but if no fan starts, the compressor will shut off on what is called an internal overload.

Customer: replied 10 months ago.

Thank you.. I think I was getting bad readings on the voltmeter. It is the cheap on and old one from harbor freight. I changed the motor not long ago.. It did not show any readings on the 24volt part of the smaller wires while showing 240v on the upper 21 black wire and 23 yellow wire. which is not normal.

I will test it again with a good voltmeter and get back with you.

Thank you

Sounds good, I think we are getting 24 to coil or else the plunger would not be down and you would not have 230 between 21 and 23.

Customer: replied 10 months ago.

If that is the case. How do I test for a bad fan motor ??

Locate the fan wires and tell me if one goes to capacitor and the other two go directly to contactor?

Customer: replied 10 months ago.

on connection 21 there are 2 wires. one goes to the compressor and the other one goes to the circuit board. On connection 23 there are 2 wires also, one wire goes to the compressor and the other one goes to the capacitor.

OK do you see terminals marked OF1 and OF2 on the defrost board?

If so, check between the wire from contactor that goes to capacitor and OF1 on board.

Then check between the wire that goes from contactor to capacitor and OF2 on board

(Calling for ac of course).See diagrams I made below

Customer: replied 10 months ago.

yes.. I'm getting 240Volts from both locations on the relay. I guess I have a bad motor..

That is correct.You have verified cap is good and you have verified voltage to motor.

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