Air Conditioner Help. Part 2

[Streff]

Good morning,

One of our rooftop ACs stopped working a week ago. when it is turned on, all I hear is a constant humming noise. When I only turn the fan On (without cooling), same humming noise.

I took the shroud off and moved the fan wheel and it seems to move freely. Nothing looks a miss by appearance.

Based on comments received in this forum. I did test the AC by turning the fan by hand while having the AC in the ON position. The AC started but stopped sometime later.

I quickly ordered a Fan Condenser from Dometic that arrived a few days ago. I installed the new condenser and put everything back together. Now when I turn the AC "ON", it runs for a minute or so (with a very loud noise) and then it stops. All that remains is a deep humming noise. Let it sit for a few minutes, start the AC gain.. same thing... Starts and stops..

Any ideas on how I can tackle this issue would be greatly appreciated.

Thank you for all your help

Simon
2007 MADP

[j-d]

There's no polarity on those things, so you can't go wrong there. If you're getting a Loud Mechanical Noise and running Fan Only (NOT calling for cooling) then the problem's somewhere with the Fan Motor or Fan. Actually FanS, since there's a fan outside and a blower wheel for inside.
I just went through a case with ours (Coleman Mach but same setup) and the fiber "wicking" that's supposed to hold oil for the blower shaft bearings had gone dry. It squeaked while running and wouldn't re-start after being off awhile.
I carry one of these oilers
and some of that oil helped. Oddly WD-40 helped even more. When I got home I dismantled the motor, cleaned everything, made new oil wicking, lubed it up and reinstalled. So far so good.
The compressor has a start winding and start capacitor. The blower has low and high speed winding, no start winding, and a run capacitor but no start capacitor. The motor has Very Little Starting Torque, so my guess, based on recent experience, is you have dry bearing(s). Ours has no oil caps or holes, relies on oily wicking. The bearing on the Blower end is pretty well sheltered. My problem was on the outdoor Fan end.
I used a lot of that Zoom Spout Oil on this project and ordered a new oiler for $7 on Amazon Prime. It sells for less (but with high shipping) and at some vendors for much more.
Adding, that in fairness, pretty much Nobody advocated working on the motor. Amazon Prime has a new one (but for Coleman Mach Plus) for a little over $100.

[Streff]

The capacitor that I replaced had the same value as the new install (ordered directly from Dometic).

Simon

[Chris_Bryant]

It just sounds like either the wrong capacitor is in there, or the wiring is wrong. There should be a value marked on the motor- like 5 mfd or 7.5 mfd 370 volt, and the fan capacitor should have that value- or if it is a dual cap, the fan needs to be hooked to the fan side, compressor to the herm side, and the common must be hooked to neutral.

[Streff]

Thank you for the input,

The noise is a humming mechanical/electrical humming; noise. Maybe the fan motor is stuck in place. However, it does start very loudly and runs for a few minutes then the noise dies down, the fan stops and what is left is the humming noise.


Maybe I should try spraying a lubricant on the fan motor and see if that helps in any way.

Simon

[Chris_Bryant]

Was the capacitor the same value as the one you took out? What kind of loud noise is it making- a mechanical noise?

[time2roll]

I am no expert but it sounds like the start coil is running the fan until the cap times out.
Probably new motor is needed.

[Lorinmc3]

If it isnt the capacitor, I would test the fan and see if the fan motor is bad.