I think you mean E5. E4 is related to an outdoor temp sensor (which doesn't affect AC).
From the description of the E5 code, it sounds like a bad freeze sensor or open wiring to it. You might try calling Dometic customer service for more guidance, but it sounds like your unit will have to be serviced.
When you get a chance, please add a description of your RV Year/Model/etc. into your Profile and/Or Signature. You can find those things in the UserCP link in the green bar near the top of every screen.