disconnected furnace, now AC doesn't work

Thanks, Doug! I sort of figured that the power to the compressor control board was the issue, but not sure how to fix it (obviously). On your advice, I disconnected the red 12voltDC+ from the blue thermostat+, and jumped the other blue wire to the red 12volt DC+, but got nothing. Connecting BOTH blue wires to the 12 volt DC+ turns on the fan, but not the compressor. It is possible that the fuse on the control board is blown, as dear husband isn't anxious to climb on to the blistering hot roof to check right now. Would a blown fuse on the control board keep the entire AC unit from running, or just the compressor?

Your problem is POWER (12 volt) to the Roof AC control board. Also, since you replaced the Wall tstat with a NON RV Tstat, that compounds your operation problem. Now, (Jayco RV's do this) they run the 12 volt positive to the FURNACE RED input wire. There are 2 BLUE wires coming out of the furnace for the Wall tstat. Those 2 Blue wires go to 2 smaller gauge wires going to the Roof AC control board OR to the wall tstat depending on how the OEM wired the system. Either way, it sends the 12 volts to the AC upper control board to operate it. Since you changed the Wall tstat, your 12 volt COMPRESSOR signal is NOT sent to the upper control board . But when you jump the 2 wires from the old furnace you send a 12 volt back feed signal to operate the fan---It takes 2 separate 12 volt signals to operate the FAN and the Compressor. And you should have Lo and Hi fan and you only have the signal for either at this time. The AC control board is what activated the furnace to run and cycle. The wall tstat sent a 12 volt signal to power that 2nd BLUE wire from the AC control board furnace relay. You will not burn out the AC unit by trial and error. You may blow the fuse for the AC control board, but will not damage the board. What you need to try at this point is to connect the furnace 12 volts to the OTHER blue wire and see if it functions. Disconnect the original blue wire you jumped. Doug

AC is a Coleman Model 7333A8664 , furnace was Atwood Excalibur 8535-III
There were 4 wires going into the furnace, +12 volt DC, -12 volt DC, thermostat, and +thermostat. Connecting the +12 volt DC wire and the +Thermostat wire causes the fan to turn on, but not the compressor.

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