Apu ThermoKing Pipes Freezing

If the pipes freezing/covered with ice for evaporator or around it when running AC - either a leak of freon somewhere in the system or bad expansion valve (about $75 for part).  

When replacing expansion valve (which is next to evaporator, under the bunk) drain freon, unscrew two nuts on outside of the big plastic box, unplug evaporator and remove it from the big black box to make it easier to unscrew the other two nuts on the hoses coming to expansion valve. Important! Hold the nuts on the pipes with a second wrench or you can damage flimsy aluminum evaporator.