A/c & furnace issues

[Wireman]

I have a 2016 23RLSW travel trailer. 4 or 5 months ago had a issue with the A/C not cooling. It's a Dometic Duo-Therm Brisk II 15K btu unit.

Made do without it on that trip. Last weekend I decided to dig into the problem.

The A/C is still not cooling, the blower runs. During my troubleshooting, when I set the thermostat to furnace, it will not run, but the A/C blower starts up.

The thermostat Hi-Lo fan position works ok.

I checked all the wiring, no loose connections. I have 12 volts to the thermostat and going into the relay control box located in the A/C unit.

LP is good. Really confusing why the A/C blower would run with the furnace turned on at the thermostat.

Leaning toward the relay control box as the issue, but would like some input from anyone.

Thanks.

[ragnarm]

We had to replace our A/C on a year old trailer. Symptoms were the same, blower runs but no cold air. Service tech checked it out and found the unit did not work. Apparently, RV A/C's are not very durable.