I have a strange problem with the AC on my 99 Rodeo. It cools great at idle but not so great above 50mph. I am thinking that the comnpressor is cycling too much at hiway speeds. Could a worn engine belt cause this? I have checked the refrigerent charge and it is OK. Thanks, Cliff

This can be one of three basic things, maybe more.
Low freon- as engine speed increases the suction (low) side pressure drops, the switch opens and the pump shuts down.
High freon- as engine speed increases head pressure (high side) goes up and THAT switch shuts pump down. A non-functional aux fan will also cause this, but at 50 mph that may be moot.
Contamanants- any moisture will raise head pressure. Replace drier (accumulator), evacuate and recharge with fresh ester oil and freon.
Pressures should be: Low- around 45psi, High- 150-200psi. Any extreme variation in these pressures may signal something else such as a restriction...Cal

Thanks TroopaDoopa ! I do have a rather high head preassure that is going up to about 300 psi which in turn is cutting out the compressor. I evacuated and recharged the sytem with the recommended 1.43 lbs or r134a but it didnt help. Does this sytem have an orifice or an expansion valve and, where is it located? I figure if I am going to replace the drier, I might as well replace the expansion valve too. Thanks, Cliff

After you evacuated the system did you pull a vacuum down to 29Hg for 20 minutes or more? Its very important to vac the system to boil off any moisture. If you skip this step your pressure readings will be high. You might be able to rent an R134a vac pump from large auto A/C shop.

Best of luck!

Yes...I pulled a vacumm for 30 minutes.

It has an expansion valve, and the valve is in the housing in the coach. You'd have to pull the entire plenum chamber to disconnect it from the evaporator. Chances are thie valve is OK, as you did say it was cooling until compressor shutdown. Put in a new drier, evacuate and charge (Don't forget the oil!). Make certain your condensor fan is working too, it'll keep pressures down whilst restrained at red lights...Cal

Whatare your pressures at idle?Make sure your fan clutch is engaging.The expansion valve is known for failing on rodeos.

20-30 lbs at idle. C

Ooo, that's pretty low for that 300# high side pressure. Now it's down to cooling fan functionality or restriction in the system. Has this system been open/empty for a while? Cooling of the condenser (in front of radiator) is essential for head pressure. I dumped my fan and clutch for thermo-electric, gave me more engine power (and a lot less noise)and colder A/C on a retro 134A in an '88 Troop. After a good evac and charge, even a saturated drier will cool for a few months.
Hard to believe the exp valve, 30 years of 911 Porche's with the same generic valve and I've replaced one, on a car 25 yrs old. Maybe Zuzu is different. Good evac and good ester oil usually cleans em as new. Keep postin...Cal

Ester oil or PAG oil? It makes a huge difference! My rodeo takes PAG oil. Many of the commercially available refrigerant cans of r-134a only come pre-lubed with ester oil, so I have to purchase the refrigerant without oil and add my own.