The A/C in my 1984 300D has been working

like a charm through this hot Florida

summer, even though my auxilliary fan is

not working. The temperature gage rarely

exceeds 100 degrees C. However, today

I carelessly let it idle too long with the

A/C on and the temp got up in the 115-

120 range. I shut off the A/C and drove

a short distance, and the temperature

quickly returned to normal. When I turned

the A/C back on the compressor clutch

would not engage and I only got warm out-

side air. I checked the fuse panel and all

fuses are fine. Is there another fuse or

relay that I have overlooked, or have I

ruined a perfectly good compressor? Is it

possible to bypass everything and get the

clutch to engage temporarily, so that I

can determine the extent of my problem?

I appreciate all the help that this site

provides, and would be happy to help with

diesel fuel injection related questions.

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kjcalhoun
Bosch certified DFI Tech
20 years experience
MBCA Member, Southern Stars
1984 300D
1985 300CD

A few things can cause this. A evap temp sensor. Low freon level. No power to the clutch or faulty low pressure switch on the drier. Turn on the system and bridge the two wires on the black switch on top of the drier assy and if the compressor comes on, you are out of freon. Usually

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

I have the same problem with my 1987 300D Turbo, the clutch would rarely engage. If the clutch does engage I get cool air for less than a minute. I've tried to bridge the two wires on the black switch on top of the drier assy but the compressor won't go on. Where is the evap temp sensor located and how do I test this?

The 87 is different in design. It uses a compressor control unit to turn off the compressor in the event of slippage. They did this to try to save the poly belt. You probably have a faulty sensor on the rear of the compressor or a bad compressor control unit.

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM