I was wondering about this. I fully realize that, in an ideal world, you are not supposed to plug your RV into a regular household 120-volt 20-amp circuit, with an extension and an adapter. But, let's assume for a minute that you have to do this. I know for most of the loads in the RV, this is probably OK, as long as you don't use the microwave/convection oven and the A/C. Now let's assume that you need to use the A/C and also that your A/C does not trip the breaker and that your extension cord is beefy enough to handle the heavy current.
Now here is my question. In such a setup, can it hurt the A/C to be running off power like that? To my mind, as long as it has power, and doesn't trip the breaker or overheat the extension cord, it ought to be OK, (not an optimal way to run), but not anything that will be detrimental to the A/C system. But, the guy at the RV Service Shop I had my RV into recently, said this does hurt the A/C, that it causes it to work harder and can be detrimental to the system.
So, if anyone here feels they are an expert on A/C Systems and would like to chime in, your feedback would be appreciated. Personally, I have done this, I do keep it to a minimum. Maybe a little while getting ready for a trip and working in or loading the RV, I might have the air on a bit.
I am in the process of installing a 30-amp circuit with a plug outside my home. But also, when on the road, I have visited family and stayed at their house 1 or 2 nights and hooked up in this fashion. As I said, I do try to keep this to a minimum.