Here is your problem.
1. That outlet in your garage is a 15 amp rated outlet.
2. The wiring to that receptacle is on a 15 amp breaker
3. ADD the length of the wire IN you walls of your house from the main breaker box to that outlet. Then remember, that may NOT be the only receptacle connected to that Garage plug. You may have other house lights or appliances using that specific circuit
4. There is a reason, ALL RV AC units are required to be on a 20 amp breaker IN the RV. They require up to 16 to 18 amps when the Compressor start capacitor system kicks in and then the AC unit (Fan and Compressor) will usually pull anywhere from 12 to 16 amps depending on the model and outside temp
5. When you take your 30 amp RV shore cord and then use a extension cord, THAT will cause a drop in voltage depending on the length of the extension cord. ALSO, there is a reason they call the adapters 30 to 15 amp. NOTE, it is a 15 amp adapter, not 20 amp
6. You cannot just install a 20 or 30 amp breaker in your house breaker box for that plug---The wiring and the wall receptacle is rated at only15 amps
7. I use a water hose analogy when describing the problem you have.
If your house was on fire and the Fire Dept showed up, WHICH water connection would you want them to use? The Fire hydrant or your outside water faucet? The Fire Hydrant of course. WHY? Because you will need a LARGE volume of water to put out the fire. The Hydrant can supply that thru the large FIRE HOSE and the size of the Hydrant exit fittings. Your wall outside faucet could never supply the volume of water needed to put out a fire
8. THAT is how electricity functions. LARGE Gauge wiring can safely supply the VOLUME(current) of electricity you need to run hi amp appliances. Doug
