Rear roof A/C not working

[Keith Moffett]

Rear roof A/C should work on shore power 50 amps or when the generator is running shouldnt it?  Ours used to work but unless I have forgotten some operational point, it no longer does.  When the thermostat is on cool and so on the A/C makes a humming noise and stops.
Any ideas?
We could replace it but I wonder about converting that one only to a heat pump.  What say you all?

Thanks
Keith

[Larry Fisk]

Personally we very seldom use the heat pump on our AC Units. When were trying to sleep on a cold night the furnace seems to do a better job and it is less noisy, I'm not sure what the problem is on your unit. I hope its not a seized compressor. Someone else should have better feedback about that.

[Edward Buker]

Kieth,

They both should work on 50amps. There is a starting capacitor that is involved with the AC motor in the compressor. This is what you are looking for located on the roof under the shroud, You could pull this item from the other working air for diagnostics.

http://eldonrv.com/air-conditioner-start-capacitor---dometic-3313107-027-3100248-420-run-start-fan-capacitor-30-50-mfd-cap.aspx

This is an example and you should check a parts list for your specific unit or get that info from Dometic. I would change the capacitor or do diagnostics per the above and see if it starts. If so fine, and if not you have a spare of this part that does fail from time to time. You can listen to the compressor with the shroud off and see if that is where the humming is originating from (not many other sources up there but just in case something odd is going on). If it is a locked compressor you would be better off buying a new air conditioner. I would just try and buy a compatible unit that does not require other changes and Dometic should be able to help you with what is compatible with your current model/ser/ unit and what is involved wiring and thermostat wise to add the heat pump version if you desire to go that way.

Later Ed

[Steve Adams]

Keith,

We had a 5th wheel and the AC had the same symptoms, hum then shut down. Bee's had built a nest inside the cover preventing the fan from turning. Clearing them out got the AC back online.

Steve

[Gerald Farris]

Keith,
It sounds like the fan in your rear A/C is inoperative for some reason. The only way to tell what the problem is to actually get up on the roof and see what is happening. If you are not comfortable in working with a live electrical circuit, you should have someone else checkout the unit. The repair can be as easy as removing an obstruction like Steve mentioned, or as complex as anything from a defective fan motor to a complete unit replacement, but you have to diagnose the problem first.

On the subject of changing to a heat pump, you need to consider that there will almost certainly be necessary changes in the thermostat system as well as the additional cost of the unit. A heat pump will also be noisier and less efficient in heating the coach than your Hurricane system. However if you are in a campground where electricity cost is part of your nightly rate, there will be some savings in using campground electricity instead of your diesel to heat the coach. Just remember when you are making the cost analysis, heat pumps will only be able to keep the coach warm when the outside temperature is above 40 degrees or so. Therefore you will probably find that it will take many years, if ever to recoup the cost.

Gerald    

[Frank Bannert]

Usually when a compressor is bad it will trip the breaker as soon as you turn the unit on, So I would think you have a bad capacitor or a shorted motor or some type of debri keeping it from starting. I would try to spin the fan motor by hand and maybe lubricate it with a drop of oil. I would try to spin the motor and have someone turn it on and if that doesn't work I would try replacing the capacitor.

[Edward Buker]

When Keith said the unit made a humming noise and then stopped I was thinking that it was most likely the compressor triggering a thermal overload breaker due to the high current. The fan motor could have self protection but I was thinking for cost and reliability probably not. Good point that the fan could also be the culprit here. Best to check them both.

Later Ed

[Keith Moffett]

Thanks to all for some good ideas and perspective.  I am getting ready to open it up.
Keith

[Keith Moffett]

Ok, you all gave me some advance warning on what to lok for and it helped alot.   I pulled the shroud and checked the fan which showed no debris but the motor was stuck.  I am thinking lack of use made the bearing in the fan sticky and it just didnt have the power on the primary circut to overcome the residue.   Ammounts to the same thing I think as the debris blocking the fan as mentioned above.
After turning the fan by hand a few times it fired up on demand repeatedly and was cold right away.
Looks like a new fan motor in the near future but not a complete replacement of the A/C.

Thanks again for the heads up, everyone!
Keith

[Keith Moffett]

By the way, there are numerous cracks in the shrouds.  Are these available as OEM replacement or must I go with the universal version?
Keith

[Edward Buker]

Score one for the fan motor troubleshooters.....Keith, good deal that it was not the compressor. I believe that the shroud should be available.

http://www.campingworld.com/shopping/item/dometic-penguin-replacement-shroud/22895    It has a Dometic number and the site indicates made by Dometic.

Later Ed

[Keith Moffett]

Thanks Ed.  yea, the fan motor may be going out but that is easier to replace than the whole unit.
Here is yet annother question for the general forum folks.
My manual (Beaver owners) indicated the A/C units as 'Duo-Therm'.  The 1998 Beaver brochure indicates the A/C as Dometic.  Since there are no labels inside or out, is there a way of confirming the mfgr. and model?

Keith

[Edward Buker]

Usually there is a label with a model and serial number located on the unit. Manuals in the coach may have the answer also, In this case Dometic is the manufacturer that makes the Duo-Therm which is the model. The shroud should look like the one in my link. So it is the same unit in both references.

Later Ed