Need help with HVAC unit (inside home) weird problem

[himybro]

Hello hvactechgroup community,

I really need help with this problem that started about a year ago. Randomly, the HVAC unit inside my house would have the weird noise as shown in the above recording. The unit inside my home (fan,motor,etc.) would stop after the noise while the HVAC unit outside house would still be running. The funny and most annoying thing is, this happens randomly. The entire HVAC could work normally for a day, few days, or weeks before the problem happens again.

I have had AC pro or technicians from 3 different companies came and inspected the entire unit. (1 was nice enough to come inspect for free!)

All of them said outside 5-ton unit was absolutely fine.
-One of them changed the motor which costed me few hundred bucks.
-The other changed a conductor thing (i think, it's a little box thing that had many wires connected to it), which costed me about fifty bucks.
-The third guy checked the wiring and wires, and changed some older ones to new ones.

As of today, the problem is still here! All of the above technicians did come back multiple times and just could not identify what causes the problem. It happens quite randomly that we have to call them to come once the problem appears; and after they arrive we would turn the unit on and off via thermostat until they really see the problem.

I am really wondering if any PRO here can tell what might be causing the weird noise and stop the unit from the recording.

Thank you,
RC

[Sergroum]

Well. Your motor and capacitor was changed. So we can assume that is not the cause.  Perhaps somewhere a wire loses contact due to vibration.  It could be a 24v control wire, Or it could be the wire that's supplying power to the motor itself.

Is there a control board somewhere there? I think the tech that changed some wiring was onto something.

[Sergroum]

His relay closing is really loud.

[DTinNC]

(msg about loud relay click) it's very loud but I'm betting that the clicking noise at the beginning of the video is likely from the circuit breakers being switched on to power the fan.

If the circuit breakers that were switched on at the beginning of the video are powering the condenser unit outside as well - then the power rush from the outside compressor etc starting could be limiting the power to the EVAP (inside) fan.  That could be caused by dirty electrical connections, undersized wires that supply the unit(s) etc.

I would bet that the surge of the fan may be when the outside compressor kicks on.

Just my 2 cents

[Sergroum]

Highly unlikely that air handler power supply is the same supply as air conditioner outside.

[DTinNC]

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