My Dometic RV Rooftop AC Unit works Great when I have the A/C ON when I cut the A/C off the Freon pump motor is still activated and freezes the lines.

sound right to me

You don't, they are a sealed unit. You can have an AC guy cut lines, solder on valves and re-charge it but the cost is usually close to just replacing the roof assy complete, then you have a warranty and all new parts as well. What is the problem with yours currently?

Open circuit or out of range Freeze Sensor. Air conditioner mode of operation will be locked out. Furnace, heat strip, heat pump and fan mode of operation can continue to operate but displays the last temperature set-point. There is a sensor that detects evaporator freezing, it may be bad or your freezing because of low freon levels

YEP ITS A 22 UNIT, . BY STICKING AC GAUGES ON IT IT WILL TELL YOU THE STATE OF CHARGE.. SHOULD BE DONE BY QUALIFIED PERSON !
JAY THE POOL PUMP MOTOR REPAIR GUY FLORIDA

its most likely low on freon and when that happens it freezes the cooling coil into a block of ice that no air can pass threw...have it serviced with a dose of freon

If the Air comeing out is the same as the temp inside the RV make sure the compressor is running and not just the fans. It could be low on freon. If freon is ok then you would need to ck the wiring to the selector switch for a short. It would be obviouse because there will be melted wires. I am leaning toword low on freon since you have already been inside the wiring/control unit.

You don't, they are a closed system, but if you can find an AC guy who is qualified, the can cut line & add valve, but can be expensive & no guarantee. Most find it's cheaper & better to replace upper unit if lack of freon is actual problem. What is unit doing that makes you think that's the cure?

My home unit was doing that because it was low in freon and needed charged.

I recommend going with a new one. Both the coleman and the carrier are excellent and a whole lot more efficient that the 16 year old dometic.

You are low on refrigerant.