Air Conditioner not working. Help Please

[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.

Any advice or guidance would be much appreciated.

Simon
2007 MADP

[Streff]

Thank you all for responding with great ideas,

The weather cleared up a week ago and 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 how I can proceed with further testing or swapping out of parts.

Thank you for all your help

Simon

[Chris_Bryant]

Most have a single fan motor driving both blowers- though some do have separate motors.

[opnspaces]

Which fan should the OP be concentrating on? I thought the roof fan was for the condenser core only and there is a fan that blows air inside the RV located behind the ceiling grate?

Yes you still might have a bad run capacitor, but make sure you're looking at the correct fan.

[PaulJ2]

Hard start cap is for the compressor motor only. Fan motor has a run cap only. Yes, it is probably bad.

[dusky203]

This....

[Chris_Bryant]

A bad fan capacitor would be my first thought. You can easily check by spinning the fan blade and turning the power on- if the blower keeps running, the fan capacitor is bad- if you can spin it backwards and it keep running, the fan capacitor is definitely bad.

[RoyB]

Usually when my Air Conditioner hums it is due to LOW AC VOLTAGE from the camp ground pedestal connection.

I always have one of these RV AC VOLTMETERs plugged into a receptacle where i can glance at it when turning on my Air conditioner. This model is great as it has the SAFE ZONE printed in "GREEN"...


Gives me the warm fuzzy feeling...

I also have this setup with me for checking the camp ground pedestals before hooking up my 30AMP SHore power Cable but I have to admit I don't do this as much as I used to..


Roy Ken

[Streff]

Thank you for the comments/suggestions.

The fan does not run at all. But it does turn by hand. So all it probably mean is that the motor is not stuck.

I will go back up in the roof and check carefully if the part mentioned above is damaged. Thank you for the tip. It's raining right now though.

What about a bad capacitor. I hear folks talking about that as a common culprit. Would that disable the fan from working?

Simon

[dusky203]

Does your fan turn at all? You might have a fried fan motor....Does your evap coil get cold?

Tim

[ScottG]

I suspect the hard start cap has failed.
Take the cover back off and look for a black thing with two connections on top thats about the size of a roll of half dollars.
It may even be physically damaged - look to see if the top is lifted and/or leaking stuff out of it.
This is a cheap part and you should be able to get one from any RV supplier.

Here's a fuzzy pic of a failed part: