My rear air compressor stopped working yesterday while on the road. I suspect it is a blown start capacitor. Not sure how it happened, but my front air capacitor blew last summer while using using the generator. Cummins checked out the generator and everything is operating fine. Any ideas?

There was a bad batch of start capacitors manufactured around the summer of '06.

All of the replacements have been OK.

Both of my AC's had to have the start capacitors replaced.

Replaced 2 on front - 1st replacement was not tied down correctly. Has anyone had a run capacitor go bad? I ordered both (start and run) as spares. Any tips on installation?

Certainly run capacitors do go bad but not nearly as often as the start cap does. Be sure to turn off power before starting to work on the unit at the circuit breaker and tape it off so someone does not hot it back up while you are working on it. Remove the shroud and the cover on the side of the roof unit. Be sure to short out the terminals of the capacitors to each other in case there is any stored voltage in the capacitors. There is not polarity on capacitors but you may find a dual capacitor that feeds the compressor and the fan motor. One terminal will be common and then one is Fan and one is Herm (for hermetic compresor). Be sure to wire new capacitor in this case properly. Reassemble the unit and turn the power back on.