I just went on a 550 mile round trip this weekend to Walla Walla WA (Don't say it, my wife set the destination.) Eastern WA is in the mid 90s as the ambient daytime temp. There are plenty of long, fairly steep grades. Engine temp sometimes got to 100C mark at average speed of 75-80. AC worked on the outbound leg for 2.5 hours then started to blow warm air. I had to pull over, stop and immediately start the engine and the AC would come back on. AC then got intermittent and, in one of the hottest areas and with sunshine streaming in the windshield ( wife did not like this very much), would not blow cold unless the stop was longer. At this point, it would take about 30 seconds to get cold. On the return leg, the AC worked perfectly even with 2 brief stops for 4.5 hours.

All components (compressor, evaporator, etc.) were replaced with new last fall. Have had no issues until this trip.

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87 300D 265Kmi
Factory rebuilt crate 603.96x engine at 200K