GU PATROL 4.2TD

geoff ive had the same problem when it was 50c air temp near cooper pedy and the only way was to slow down to 90k's go back to 4th turn the air con off and let everything cool down after 20 minutes allreset and away you go .its a engine protection thing ive been told so next time you go to the big smoke maybe see a air con mechanic and see if he can change the cutout switch temp.check your radiator cores to see if their not full of insects and grass seeds.let us know how you go please.cya johnsy

Geoff. This is a problem caused by peak under-bonnet temperatures and usually aflicts cars that have had an after market turbo fitted (in GU's it can also cause battery troubles). My understanding is that a high pressure switch has been incorporated into the a/c system to prevent a blowout. As the working temp' of the system rises, so too does the pressure until the switch open cicuits and shuts the system down. You may need to look elsewhere for a fix, as to bypass the switch is courting trouble

Geoff,
My GQ diesel had an aftermarket system fitted and the air supply would suddenly warm up after many kilometres on a hot day.(usually when slowing down)
Turning off the a/c for five minutes and all would return to normal.
The problem was that the evaporator was icing up,this preventing effcient heat transfer.
The problem is easily identified,as when a/c was restarted the air was getting cooler and cooler as the ice melted. The fix was to replace the t/stat which was inserted in the evap coil, meant to stop the compressor if ice build up occured.
If your compressor is cutting out on the h/p switch (high head pressure)
It could be 1.air in system 2.blocked or inneficient condensor3.if fitted ,condenser fan faults 4.lack of sufficient air flow over condenser.
The head pressure is determined by the heat rejection of the condensor,which varies depending on ambient temperature.
The only way to determine if the correct pressures exist is by connecting a gauge set. See fridge mechanic if you cannot find fault,he can determine if head pressures are correct and system free of air.