Class C with a 13.5 Dometic (Model Number: 520316.506E) year 2009My rig is parked at the house in the hot Arizona sun. The A/C works fine for most of the day but when the ambient temp hits 104 or so the compressor shuts down and the fan blows hot air. The A/C has had little use over the years. I cleaned both the evaporator and condenser coils although both were already very clean. The unit is draining as it should and the interior filters are clean. I did a voltage check over the day yesterday and have eliminated low voltage as the problem.I have been advised on another forum that the issue could be the overload protector (thermal switch) which is designed to shut down the compressor when it's too hot. So I figured I would just replace it. Problem is that it looks to be internal to the compressor. Any ideas? Thanks.jorCompressor Photos

I am dragging up old memories here, so there may be other problems. I replaced a number of over temps that were in the terminal box that was held closed by a spring, and most of those were held against the side of the compressor by a flat spring that dogs into said box. If yours is like that, you may be able to change out the over temp switch. The trick is going to be getting a replacement. That sure is not a big box or hardware store item. Look for a refrigeration parts place or a Grainger. Best of luck.Matt

terminal box that was held closed by a spring, and most of those were held against the side of the compressor That's the thing. Nothing attached to the compressor. Just that barrel-line component which looks like it is pressed into the compressor container. I added a link in my original post to a couple of photos.

In the box should be capacitors. Used to start compressor under load and other for run. Inspect the capacitors for any sign of bulging. (swelling)Make and model of AC unit?

Capacitors do age. and dry out or otherwise fail.And the compressor may just flat be too hot. And thermal cut out engaging 104 is a bit on the high side for their designs.one thing that might make it better.. OR WORSE depending on things like mineral content of the water is a "Mister" near the air intake for the condenser. They sell them but the nozzles clog easily (I had 2)

Dometic (year 2009)Model Number: 520316.506EI'll take a close look at the capacitors mañana in the morning. Thanks.jor

Roof A/C Issue | Good Sam Community

dougrainer
Nomad
Jul 22, 2022
joraz wrote:
OP here. All fixed and blowin' cold. The solution turned out to be simple and at the best cost - free. After searching for capacitors, thermistors and thermal overload switches, I simply reset the Dometic 5-button and whadayaknow, success! Thanks to all. I now know a lot more than I did about that roof a/c!
jor

HAPPY THAT IT IS RUNNING. But, doing a 5 button(or 10 button) reset does NOTHING to fix your problem. ALL a Dometic reset does is verify the DIP switch settings on the upper control board. Nothing else. Please post if the original problem comes back. Doug
joraz
Explorer
Jul 22, 2022
OP here. All fixed and blowin' cold. The solution turned out to be simple and at the best cost - free. After searching for capacitors, thermistors and thermal overload switches, I simply reset the Dometic 5-button and whadayaknow, success! Thanks to all. I now know a lot more than I did about that roof a/c!
jor
dougrainer
Nomad
Jul 19, 2022
joraz wrote:
I need to know if your wall tstat looks like this

No, it's a 5-button Duo-Therm Comfort Center (photo here thermostat).

Speaking of the thermostat, yesterday morning I reset it according to the directions. It got up to 102 or so yesterday and that a/c didn't miss a beat. It's 101 right now and it's going strong.

One other thing, before I reset it, I would turn it on and select cool. There would be a significant delay before the fan came on. Now, the fan starts up right away. Could be this is my problem. Keeping my fingers crossed.
jor

Sorry, Brain fart. I missed 2009. There is a Freeze Thermister that is inserted into the evap. Does your model AC have the inside removable air filter plenum cover? If so, make sure that thermister is inserted into the evap. Doug
joraz
Explorer
Jul 19, 2022
I need to know if your wall tstat looks like this

No, it's a 5-button Duo-Therm Comfort Center (photo here thermostat).

Speaking of the thermostat, yesterday morning I reset it according to the directions. It got up to 102 or so yesterday and that a/c didn't miss a beat. It's 101 right now and it's going strong.

One other thing, before I reset it, I would turn it on and select cool. There would be a significant delay before the fan came on. Now, the fan starts up right away. Could be this is my problem. Keeping my fingers crossed.
jor
dougrainer
Nomad
Jul 19, 2022
I need to know if your wall tstat looks like this? Doug

https://www.dometic.com/en-us/outdoor/climate-and-comfort/air-conditioners/air-conditioner-accessories/dometic-ct-single-zone-thermostat-164511

The reason is simple. Even tho your RV is 2009, years ago Dometic had thousands of single Zone tstats that had a SIMPLE fault. If the interior of the RV was over 95 degrees, then the tstat failed to function. The only fix was a new updated Tstat which removed the heat failure problem. A way to test this was to take a PC air can, turn upside down and spray the cold on the tstat for a few seconds. If the Tstat and system functioned the tstat was your problem.
joraz
Explorer
Jul 19, 2022
Here is a parts list

Thanks a million!
jor
enblethen
Nomad
Jul 19, 2022
Here is a parts list and link to parts breakdown.Parts list and breakdown
joraz
Explorer
Jul 19, 2022
That is a dual capacitor.

Thanks for the explanation.
jor
prichardson
Explorer
Jul 19, 2022
That is a dual capacitor. The 60uf side is for the compressor and the 12.5uf side is for the fan motor.
joraz
Explorer
Jul 18, 2022
After taking in all the comments I think I'll replace the start and run capacitors and the thermistor just in case.

I had intended on jumping the thermostat wires today but it's just a circuit board. Anyhow, I did reset the thermostat and it's running fine now with 101 degrees outside.

Now the problem. I found a start capacitor with matching numbers here: start

...but I am confused about which run capacitor to get. I have four lines of numbers. The last line indicates 60+12.5uF and 370 volts so I guess that 12.5 is the capacitance and the 60 maybe the frequency? Anyhow, this one looks like it could be it: Run

I'm just out of my area here. Thanks.

I've linked to a photo of my capacitors here: capacitors
jor

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