In Reply to: Re: Re: Re: Re: Re: Re: m2 blows 20 amp fuse when ac is turned on posted by tractorjockey on June 18, 2009 at 11:39:36:

With the AC mounted down the back together with the batteries, there is a lot of wire to carry a fair current between those batteries, up to the cab switch and back down to the AC compressor.

Placing a relay into the system to carry the heavy current load over only a short distance from battery to AC compressor reduces the current into and out of the cab AC switch and wiring system down to milliamps to switch the relay [s] and will help overcome any serious resistances that have arisen in the wiring loom over the years.

Relays for the condenser fans and the cab fans also help a lot rather than relying on [ overloaded ? ] cab switches and long wiring looms to carry the full current load.