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DruidZ · 03-18-2025, 03:30 PM

This is a strange problem we are having. We have three units and numbers 2 and 3 work but 1 just runs the fan. We have replaced the control board twice. If we put power to the compressor it it runs. If we run diagnostics command 5 it runs.

After talking to Dometic many times they are now telling us that it is a ground problem that they can't help us with. I don't understand that. The control board lights up, the wall unit works, a test version of the wall unit plugged directly lights up but no compressor.

Has anyone seen anything like this and can you suggest the next thing to try?

RVfixit · 03-20-2025, 01:02 PM

Hi, Sorry to hear about your problem with the A/C. To try to help diagnose this issue, can you provide the year and model number of the A/C unit, or just send a picture of the ID tag? We can then go from there, Thanks

DruidZ · 03-21-2025, 02:13 PM

Here is the label. Looks like it was made in 2015. A bit old but the compressor does work and we have tried three different boards now. The switches are set correctly with all off except for "furnace". We disconnected the wire going to the other two to isolate it. The wall unit was replaced by putting plugging in a test one directly on the roof. We are baffled.

RVfixit · 03-23-2025, 11:51 AM

Thank you for the picture! So, it appears you have a Dometic Penguin 2. There are many things that can cause the compressor to not start on its own so lets start with the simple things first-

1) Your unit has three main sensors all of which can cause the compressor to not start; You have a freeze sensor in the evaporator coil that will turn the compressor off if it senses a frozen coil

2) you also have a sensor in the unit on the roof that senses outside air temp and will prevent the unit from starting if it thinks the outside air is too cold and last,

3)you have an inside temp sensor that will shut off the compressor if it senses the temperature setting has been met.

The one to start with is the evap coil freeze sensor. Its the easiest to fine since it is stuck into the coil or mounted onto the surface of the coil which you should be able to see when you remove the filter cover. To test, follow the wires to the control board and simply unplug it. Try running the ac and let me know what happens. If your not sure which one it is, after removing the inside filter cover take a picture of the evap coil so I can point it out.

Larry

DruidZ · 03-24-2025, 04:16 AM

Thanks, Larry. Before I have my guy climb up and try that, can you confirm that command five in the diagnostics will still start the compressor even if one of those is a problem. The compressor does start in that case.

Thanks.

RVfixit · 03-24-2025, 10:24 AM

Ok, I didn't know you had the command 5 system. Have you tried doing a full reset of that system yet? It would involve shutting it down at the control panel and then rebooting it at the BCM module. If not, if you could give me the model number it would help me confirm the reboot process. Thanks

DruidZ · 03-24-2025, 02:04 PM

Do you mean initialize? We have done that a few times. That's a matter of holding down the zone and mode buttons when it is off. Are you talking about something else?

I can't remember the button combo to get into diags. I would love to see what command 8 says. That shows the sensor reading or error. We might find the problem without even going on the roof.

Isn't the model one of the numbers on the label I posted?

DruidZ · 03-25-2025, 08:44 AM

Finally found the information on putting the CCC2 thermostat into diagnostic mode. I checked command 11 specifically. Zones 2 and 3 didn't quite match the current ambient weather but zone 1 was showing -05°F, obviously total nonsense. I just ordered new sensors for all three. In fact, Amazon had them for about $20 for five of them:

https://www.amazon.com/gp/product/B0...1?ie=UTF8&th=1

Will let you know how it goes.

RVfixit · 03-25-2025, 11:26 AM

After making the repairs, make sure to connect everything back up as normal and then test. If there are still issues, locate your body control module (BCM), inside is a reset button. To use the reset, you must first turn the panel off so that it was a blank screen, then do the reset by holding the button down for a few seconds, then turn the system back on. I'll try to find some pictures just in case you need them. Good Luck and let me know how it goes!

DruidZ · 03-27-2025, 04:36 PM

We replaced the sensor and now it works fine. Our repair guy was on the phone so often and they never mentioned the sensor. I guess their phone support is no better than computer support. "Did you try turning it off and back on" level.

The thermostat is a CCC2 model so it is a little different. To initialize you turn it off and then hold the zone and mode buttons down. See my previous message for diagnostic details.

RVfixit · 03-28-2025, 10:31 PM

I’m glad you’re up and running again. I’m retired now but having worked in the automotive/heavy truck industry for many years as a mechanic years ago and then in construction management for the last 20 years it has always been my routine to verify the simple things first. It has never steered me wrong. It’s sad to say but most technicians today use computers for prompts on diagnostics and often have no knowledge of what they are even working on.

As always, Safe Travels!