Paul, (Hattieville, AR)
With the power to the coach disconnected, open the EMS cover to expose the electrical connections. First make sure all the high voltage wiring is in place and tight. Check the white/neutral and bare/ground wires to make sure they are tightly secured to the neutral and ground bars. Ensure the black/hot leads are secured to the relay terminals and the circuit breakers. Such connections have been known to vibrate loose during travel. Also, make sure the shore power cord passes through the current sensor loop inside the EMS. Near the top right corner of the board you will notice a fuse, (not shown in drawing). Remove the fuse and inspect it to make sure it is not blown. It is probably a 3A/12V fuse. Near the fuse you will see a multi-pin connector. Unplug the connector and probe pins 1 and 2 (the two uppermost pins) on the harness end and make sure at least 12-volts DC is measured going into the EMS electronics module. If not, check its fuse at the 12-volt DC distribution panel. If the fuse tests fine and you have a healthy 12-volts DC entering the module, it’s probably time to have the complete EMS system tested by a qualified RV service technician. A fifteen volt drop to 105-volts AC is approaching low enough to cause damage in the air conditioner. There is the possibility you may have an internal problem with a relay or the board itself.