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

my a/c did this couple of times too. it works fine espeacially after recharge but sometimes it would blow warm and i have to restart the car and it would blow cold again. i were suspecting climate control unit since i replaced buttons on it and it didnt come out well because i had to incorporate w126 buttons in it but anyway i see that you have same problem so it might be something else. does anybody else have same problems? and anyone fixed it?

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1999 ML430 Silver 135k ml
Smoked LED taillights, Alpine in-dash DVD player, 12" sub, Pioneer components, 2 amps, 4200k HIDs, ML55 headlights, 20" rims, mirror LED blinkers

SOLD. 1996 E320 145k ml. Burgundy

SOLD but miss it everyday 1992 500sel Black
Chime buzzer mod,Alpine CD/MP3 player with stock amp,Euro headlights,S600 grill,20" rims, BEST CAR EVER!

SOLD. 1990 300E White
187k ml,smoked tails,Euro headlights,17rims,Intake,12" sub in first aid kit,alarm/autostart,buzzer mod

Sounds kinda like what I'm dealing with:

Weird C280 A/C Problem - Long Read

The 1987 300D has a circuit which compares the RPM of the compressor to the engine. If the two differ enough the compressor is disabled until the car is restarted.

There are about a half dozen possible causes for this problem. The two simplest and most common are these - 1) Grease/oil on the compressor clutch. Hey, it's an old car and these diesels get grimy under the hood. Get a spray can of degreaser or brake cleaner and spray liberally into the compressor clutch gap. Rinse with a hose, if necessary. Sometimes this is enough the cure the problem. 2) Excessive clutch gap due to normal wear and tear. Measure the clutch gap with a set of feeler guages. Should be 0.50mm. If substantially greater than that, you've found your problem. My personal observation is that clutch engagement becomes flaky when the gap reaches 0.80-0.90mm. Gap can be corrected by removing the clutch plate (special puller required, available at Autozone) and removing or swapping out the shims behind it. Not too difficult a job.

- JimY

Jim Yuhn is a very patient and helpful man. This must have been described at least 100 times since I've been posting on mshop and about fifty of those descriptions were probably done by Jim. A quick search will pull up this solution.

Have a great day,