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Randall
Randall, RVIA Certification
Category: RV
Satisfied Customers: 10414
Experience:  RVDA/RVIA Master Certified Technician with many years experience.
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My dometic prod.#991762447, a/c unit runs awhile then

Customer Question

my dometic prod.#991762447, a/c unit runs awhile then stops/hesitates then only the fan blows, after a few min. the compressor kicks on again..over and over...3/4 year old unit and a/c only used maybe 6 days per year.
Submitted: 1 year ago.
Category: RV
Expert:  Robert replied 1 year ago.

Hi my name is Robert...

What power source are you plugged into? Are you using an adapters or extension cords on the main cord?

Robert

Customer: replied 1 year ago.
direct to park electrical, have tried both 30 and 50 amp and also my generator, it all gets the same effect.
Expert:  Robert replied 1 year ago.

OK

I would shut the breaker off and check all your connections going into the AC unit. You may have to pull down the interior cover to access the wiring, look for any wire nuts and make sure are tight and not loose. Since the compressor keeps cycling on and off I might replace the start capacitor, you will have two capacitors, a run capacitor and a start capacitor. The run capacitor is for the fan circuit and the start capacitor is for the compressor, it assists the compressor for starting. They are located top side and will be round cylinders. Very important that you do not touch across the posts as they do store energy. Robert

Customer: replied 1 year ago.
How do I check if its a bad capacitor? where can i purchase a new capacitor if needed, what else might it be causing this cycling?
Customer: replied 1 year ago.
will the start and run capacitor be marked or look different from each other?
Expert:  Robert replied 1 year ago.

Let me see if I can locate a service manual for you, it will show the capacitors and testing....

Robert

Customer: replied 1 year ago.
ok thanks
Expert:  Robert replied 1 year ago.

OK

Click HERE this is the only service manual I have and it will point out the capacitors and have some testing, it should give you some knowledge of that AC unit...

Robert

Customer: replied 1 year ago.
how do I remove the start capacitor from the top of the compressor?
Expert:  Robert replied 1 year ago.

Normally the capacitor is on it own and will be away from the compressor. It will be a round cylinder with wires going to it....

Customer: replied 1 year ago.
the capacitor is embeded in the top of the compressor....can i send you a picture of the situation
Expert:  Robert replied 1 year ago.

Yes you should be able to send a photo with your reply.... Robert

Customer: replied 1 year ago.
ok here is a pic...i hope
Expert:  Robert replied 1 year ago.

OK

The ones I have dealt with will have two separate capacitors. Do you have a different number for the AC unit? Follow the wires from the other capacitor and compressor and make sure it is not under a shield. IF you can not find it I will put your question back up for other experts.... Robert

Customer: replied 1 year ago.
Here is a pic of placard and one of the other capacitor
Expert:  Robert replied 1 year ago.

OK

Found a wiring diagram, click HERE and scroll down. It shows on that model a comp. start assist. Follow the wires from the other capacitor and see if they are going to the compressor.

Customer: replied 1 year ago.
OK, I followed all the wires and this must be the * "not used on some models" model that doesn't use a start capacitor.
Expert:  Robert replied 1 year ago.

OK

Sorry I am at a loss on this, I am going to put your question back up for other experts, my goal is for you to have the best answer possible. Another expert might have some more input on this model..... I do not know when an expert will respond they come and go daily... Robert

Expert:  Randall replied 1 year ago.

Please print out or at least Bookmark the following link to the Dometic A/C manual which we will use here. Thanks! I will read the whole thread and get back to you. R.J.

http://bryantrv.com/docs2/docs/acservice.pdf

Expert:  Randall replied 1 year ago.

This should have a start capacitor which I don't see in the photos you sent. See that section of the manual. I do believe that this problem is more of a short cycling issue, which is caused by an air leak between the incoming and the discharge air. When they mix, the air flow is cooled too fast and the compressor shuts down and won't start again very quickly. It can be a control issue as well in the thermostat. Is this a ceiling discharge or wall mount thermostat?

Customer: replied 1 year ago.
wall mount, digital. the stock one that came with it,, Its a prime time if that helps.. I will check for air leaks from output to intake..
Expert:  Randall replied 1 year ago.

Is Prime Time the name of the thermostat?

Customer: replied 1 year ago.
I sealed up some air leaks that allowed cooled air to be sucked right back into the intake. I am watching the roof top unit with the cover off and one of the pipes begins to frost up and a couple minutes later the compressor shuts off but the fan continues to run......the manufacturer of the trailer is prime time..
Expert:  Randall replied 1 year ago.

O.K............then this is probably a bad freeze control. That keeps it from freezing up and shutting down. Rare that those go bad. That plugs or clip into the fins on the discharge side. Some are a metal disc and some are just a sharp pointed probe. Those are not expensive. And just to be sure, I would check the incoming AC voltage to be sure that isn't an issue. You want to see something over 115 VAC if possible.

Customer: replied 1 year ago.
ok, I saw that on the fins. haven't checked voltage but running compressor draws around 8 to 10 amps
Expert:  Randall replied 1 year ago.

Not unusual for the compressor when starting out..........check the freeze control as per the manual on that.