AC runs and cools, but fan won't spin

LaRea

Maybe somebody here will have a suggestion before I start blindly troubleshooting.  Dometic 16k air conditioner:
* Gets cold fast
* Fan would not spin in any mode, including manual fan
* I installed a new fan, and it worked great ... for a few days
* Now the new fan won't spin
* Display/controller is fine (no change when I swapped in a known good controller) 

I'm sure the cooling side is healthy; if I leave it on for a while, it will frost over because there's no air blowing.  

YYZRC

On my home AC unit I had that issue and replacing the capacitor solved it. If you spin the fan by hand with the compressor on will the fan stay running?

Since you have multiple units, maybe swap a capacitor over to test (assuming they are the same)?

Dream_Inn

I'm agreeing with a cap.  The startup cap may be just on the edge and with a new or different fan could be enough to allow it to start up.  As YYZRC mentioned, if you have a way to get the fan moving safely, it may allow it to start up.  Remember if playing with caps, you want to discharge first.  I'd say you could temporarily bypass it, but that isn't great for the fan motor.  If you have another to put in, that is the best bet.

LaRea

Makes total sense.  I'm guessing it's this one:

https://www.amazon.com/Dometic-3313107-027-Fan-Capacitor-MFD/dp/B00T36X37O

Dream_Inn

It should be easy enough to try one from another ac unit first if you have it.  Just in case it’s not the problem 

captkevin

Thought the capacitor was needed to give the compressor a boost at start up. Isn't there a fan relay that could be causing issue?

PickleRick

Ive not looked at the AC on my boat but the split unit ac in my home has a separate capacitor for both the fan and compressor....and I've been shocked by both!!!

rasbury

What do you mean by split system in your home?

captkevin

https://www.amazon.com/208-230V-Conditioner-Ductless-Pre-Charged-Refrigerant/dp/B0C73BJCG7/ref=sr_1_4?crid=27HBX9SHSGXIZ&keywords=split+system+heating+and+cooling&qid=1693525930&sprefix=split+sy,aps,351&sr=8-4&ufe=app_do:amzn1.fos.2b70bf2b-6730-4ccf-ab97-eb60747b8daf&th=1

Ian

Most AC (alternating current) motors have a cap that provides the boost to start the rotor spinning. Often home units have a dual cap in one can - one does the fan, the other the compressor.

Ian

LaRea said:

Makes total sense.  I'm guessing it's this one:

https://www.amazon.com/Dometic-3313107-027-Fan-Capacitor-MFD/dp/B00T36X37O

OEM good but any with same or better voltage and capacity specs will work. And this is a dual cap can.

LaRea

Thanks guys -- it was the capacitor, confirmed by swapping with a known good one.  Amazon has a 25/5 cap for $13, so I ordered two for delivery tomorrow.  

YYZRC

So what are you going to do with the remaining $987 you had budgeted for this boat repair?!

LaRea

Gonna go buy a sweater.  With both air conditioners running in the bridge, it'll be chilly up there!  

YYZRC

Sounds like cashmere is well within your budget. 

PickleRick

rasbury said:

What do you mean by split system in your home?

The heat pump compressor is outside my home and the refrigerant lines run under/into home where the exchanger and blower are located.