I have two RV trailer plugged into my garage 120VAC 15A and 20A receptacles. I can run everything in the RV trailers including air conditioners... The 15A and 20A service is plenty of power to run an air conditioner. The thing you cant do is run several other high current appliances at the same time. i.e. I cannot be running my air conditioner and then turn on the microwave unit in the trailer. It will trip the garage circuit breaker real quick.
To make all of this work for me was to use a 10-gauge heavy duty 50-long long extension cord plugged into the garage receptacle. Then on the other end of the 50-foot long extension cord I use a RV30A-15A 18-inch long adapter (Available at Walmart) and plug my 30A trailer shore power cable into this adapter.
I also am aware of the AC voltage coming from the garage and if it is low I will not turn on the air conditioner. I also am very much aware on the connections being made and if they are more than warm to touch I will use a different type adapter. The 18-inch long adapter seems to work best for me. Those little black round RV30A-15A adapters always seem to get hot on me as I use them. When heat is being generated than you are losing current for the trailer to use. Also the cheap extension cords you buy from Lowes and Walmart will also get hot on you and burn up the connectors. Got to use at least a 10-gauge (10-3) extension cord if you don't want to have to worry about it...
This is the RV meter I have plugged into my trailer to be aware of the input 120VAC coming form the garage. Note the safe zone GREEN scale.
This is the RV30A-15A 18-inch long "DOGBONE" type adapter I use here... Never get more than warm to touch.
Dont confuse the 15A/20A service with what you get from a 2KW Honda type generator on running your trailer air conditioner. The 2KW Honda generator only produces around 12AMPS of service which is right on the border line of making the air conditioner work in the trailers.
Been using the garage 15A and 20A service for my two parked trailers here at the house for several years now with no ill effects. Plug/em in .... I carry a RV30A-15A 18-inch long adapter and 10-gauge 25-foot extension cord with me on trips. You never know when you might want to hookup to 15A/20A 120VAC service somewhere. Good Plan-B back-up items to have aboard
My take on using 15A and 20A standard house 120VAC service...