Dometic A/C and CCC1 Tstat E1 error

E1 means that the COMMUNICATION cable from the wall Tstat to The roof AC control module is open or missing/bad connection. This is the 4 wire cable that looks like a Phone cable. It is NOT a phone cable. It is wired in reverse from a phone cable. Most common problem on a unit more than 1 year old is the Phone type plastic modular connection at the roof AC area is corroded from the humidity from the Upper AC unit. You don't state what year model RV or model roof AC. I ALWAYS replace the RJ11 ends behind the wall tstat and at the roof AC. That removes a possible bad connection. If the upper modular is corroded you have found your problem and replacement is also required. If this does not fix the Intermittant problem then the cable from the wall tstat to the roof will be suspect. Doug

PS, IF you have Penguin model AC units, then the odds of corrosion on the connection by the evaporator is almost 100%. Replace all connectors if you have more than 1 roof AC unit.