I tried the search function but couldn't get any info to come up. My AC quit working today. Blower works, vents work, but no cold air. I checked the #5 fuse. It seemed OK but I replaced it anyway. When I hit the AC button on the climate control unit I cannot hear any relays clicking nor does the engine slow down a bit indicating that the compressor has kicked in. Other than low R-12, what are the reasons that the compressor is not actuating?

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1986 560 SEL (159K miles)

Is the clutch kicking in? You can watch it while someone hits the button? If it does not kick in, either the refrigerant is low, or the sensor on the compressor is sensing a slipping belt. If it is a slipping belt, it should come on momentarily again after turning off and restarting the engine. Have someone start while you watch the clutch.

Is the air HOT or just not cold?

Good luck,

Low refrigerant, bad low pressure switch, bad AC clutch wire, bad clutch. No speed sensor on the V8s, separate belt, but the belt could be broken, too. Bad relay for the AC clutch.

What I would do:

Check the belt. If missing or slipping badly, replace.

Check the low pressure switch by pulling the wires off (top one, I think, on the reciever/dryer) and touching the wires together. If the compressor comes on, you have a leak and no freon or a bad switch (if it cools properly with the wires touching, it's a bad switch). If the aux fan comes on, you have the wrong switch, try the other one. Bad switch requires venting the freon, have a shop replace it so they can recover your freon for you.

If nothing happens, fine the wire to the compressor clutch and disconnect it, then jumper the compressor end directly to the positive battery terminal. If the clutch engages, relay is probably bad. If it clicks but the compressor doesn't turn, either the clutch is bad or the compressor is locked up (this will stall the engine).

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Found the problem......the main dual AC hose that connects to the back of the compressor is old and leaking. MB/Tacoma quoted me a price of $396. Fast Lane wants $222. Pretty easy choice on where to get the replacement. Thanks everyone for your input.

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1986 560 SEL (159K miles)

When My 140's AC leak due to rusted out hose, the price of a new replacement was over $300. I called a local A/C hose repair shop, the cost was $25 labor +$5 part =$30. It is much cheaper than a new hose.

Jack