Chassis AC Kills Ignition

[drnitrous]

Ok guys, got a pretty bizzare one for you regarding chassis a/c on a 02 Monaco Dynasty Regal 400ISL. When I bought this thing a year ago the chassis a/c was not functional. I jumped the low pressure switch and as suspected it was pretty low on freon, added freon. Compressor runs fine, no noise, cycles correctly on a/c, stays engaged on max a/c, and has a temp drop well over 20 degrees from ambient. Whew hooo, got chassis air, works great. Heading to Denver to a points race, make it 40 miles and Bertha dies, dead in the water. Engine cranks like crazy but no fire, can't hear the lift pump either with key cycled on/off, bottom line, no ignition. Cycled the master battery switches, zoom, fires up and off we go, obviously a stuck relay or thermal switch, right? So I thought. Make it another 40 miles or so, same routine, except this time cycling the cutoffs does not work. Great, so I call coachnet, they attempt to be helpful, start setting up a tow. If things aren't bad enough up pulls a "scale boy." Gulp, I'm 80 ft long with my trailer. He walks around the rig three times, says it all looks safe, asks if he can help, then leaves, day just got a little better. After sitting an hour, still talking to coachnet, reach over turn the switch and it fires, WTH? Nobody in the locale will touch a class A, only place is Cummins Central Power in Kearney, NE or another place in Linclon, NE both 80 miles away. Kearney is on the way to Denver so off we go. I shut the chassis air off and leave it off, as that's the only thing I changed from many other successful trips. No incident. The guys at Kearney were great, worked me in after hours, put them in your western Nebraska address book for future reference. No fault codes, tested the charging system, cleaned all the connections, they could find nothing, Monaco said, hmmm, sounds like a bad relay. We start looking at the wiring diagrams and there it is, the thermal switches and relays for the a/c compressor are side by side on a great big copper common, its a huge heat sink. Think I figured out why the previous owner didn't run chassis air. Since then I've put on 3000 miles without chassis air and no problems, but its 100 degrees, chassis air would be nice. The Cummins guys feel the A/C current draw is heating up the thermal switch for the ignition and tripping it, which really is about the only thing making sense. The freon was a little bit on the lower side so perhaps the compressor is cycling more than I thought which likely increases the current draw and heat production on the common power strip. The A/C worked great right up to the point the engine died so I don't think its thermal switch triggered. The Cummins guys said some of the newer OTR trucks have the AC fan tied in with the ECM which could do that, but they didn't feel it was the case with this ECM. I'm looking for input, especially if anyone has ever experienced this issue. I searched the forum and didn't see it. At this point I'm considering wiring in a seperate relay with thermal switch isolating this from that main powerbar, of course I realize that is a bandaid fix as there is something causing it, either a weak thermal switch on the ignition switch or excessive current draw from the compressor, or????? My knowledge base on automotive AC is pretty good, but there may be something else I'm missing on this one. Thanks for your input in advance. Attached is a pdf of the wiring diagram.
Thanks,
Brent

[Robi.1014]

Wondering: did you remove the jumper after you filled the system with 134a?

Thermal breakers do fail. I think replacing it can be a good troubleshooting step rather than bypassing it by way of re-wiring the A/C current load. The A/C cycling on/off should not be a cause to overhead the thermal breaker.

Also suggest insuring that the fan at the evaporator radiator is turning freely, not binding, etc.

[drnitrous]

Robi,
Thanks for the reply. Yes, I removed the jumper, honestly, didn't think to check the evaporator fan, good idea. The thermal breaker for the ignition works fine as long as the chassis ac is not running, but I have considered perhaps it is on the weak side. The thermal breaker for the ac never triggered. Guess what I need to do is check the current draw on the ac and make sure that circuit isnt pulling a bunch. The reason I posted is I know it isn't as simple as bypassing it, there is a problem, just wondered if anyone else had seen it.
Thanks again!
Brent