I have a 2003 FWD with the 2.7L engine (and 175,000 near flawless miles). The past 2 summer seasons, I have developed a problem with my A/C system, that is: when traveling on the highway (heading toward or north of Las Vegas, middle of the Mojave), going uphill with an outside temperature of 90 degrees plus, my air conditioner will stop working. Coolant temperature rises slightly, the dash gauge moves up a half a tic, my meter says coolant temp is about 235 degrees, but the dash gauge doesn't get close to the overheat mark. When things cool down (below 230 degrees), it still takes 5 or 10 minutes for the A/C to start cool air again. On level ground around town with relatively cooler air temperatures it's never a problem.

My mechanic accidentally cracked and replaced my original radiator, so it's new (but that's when the problem first surfaced), I have recharged the A/C, flushed and replaced the radiator coolant, but that hasn't helped. My mechanic thinks it might be a "lazy" thermostat, which I will replace this weekend, but I think it's a substandard radiator.

I am wondering if anyone else has experienced a similar problem, or can suggest a different/better fix. Thanks.