Dave:
Could be many things....some more likely than others; however, when I had an issue with our a/c it turned out to be a loose wire nut in the control section of the rooftop unit.
Other possibilities include:
- iced up due to fan not working or a clogged filter/fins
- lack of freon (leak somewhere?)
- bad/stuck compressor
- burned out component like a capacitor
- frozen/stuck reversing valve (if your unit is a heat pump)
- a/c compressors use a lot of power, especially on startup....are you on generator or shore power?
I would take a quick look at the rooftop unit and see if there is any obvious problem (burned areas, loose wires, unusual noises)
Many a/c problems can be identified with a volt-ohmmeter and a troubleshooting guide, if you have access to those.
The good news is that an RV a/c unit is like any other and any HVAC company can help you out.
Strange problem to have on Christmas! Happy holidays!
- Mike