Some things never switch over to 120 VAC. Lights stay 12 volt all the time. Your fridge should have a button above the door that says, LP/ Auto. Press the button, and it will switch to 120 VAC all the time, or go to 12 volt (for the internal mother board only) and LP (for the heater-tube, that evaporates the ammonia. Regardless it will still draw from 12 volt, since that is how the mother board is powered. The 120 VAC simply heats the element. (Seems counter-intuitive to use heat to make cold, but that is how it works)
The water pump is ALWAYS 12 volt. No matter what you are plugged into. If you are hooked up to city water, then simply turn off the water pump, at the pump switch. City pressure will be enough.
Your water heater is able to run on propane and sometimes on 120 VAC, which is a little black rocker switch on the front of the water heater itself. Open the gridded cover outside, and look under the burner. If it has the little rocker switch, AND the tank is already full, then turn it on, and it will keep the water hot around the clock (ONLY if tank full, and coach plugged into 120VAC, also known as "shore power" )
If you leave it on propane, it will come on every once in a while. I save propane when boondocking, by leaving the water heater turned off until I need it for a shower. It will stay hot all day without running.
I have full timed in an RV for many years, on and off, and owned RVs for the last 40 years. There are a few tricks that once learned will tide you over on any RV you use.
Buffalowinter brings up an important issue: Many power supplies in RV parks have inadequate wiring, and or incorrectly wired power. I have a "Progressive EMS" which plugs into the post and into the power line going to the trailer. It automatically diagnoses the condition of the post, and if OK, show that on the read out, then allows electricity to flow. If there is an error (insufficient voltage, open ground, excess voltage, or other problem) it will show that, and then not allow power to flow. If you have a MultiMeter, then always check the post before plugging in.
Before plugging in, make sure the breakers on the post are thrown off, after testing and before plugging in. Inspect the plug holes for signs of arcing, and before you close the breakers, push in and pull out the plug a couple of times to make sure the fit is tight. A loose fit can lead to arcing, and can cause overheating or a fire, or other damage.
good luck.
