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Wagon: mb..heater and fan works , has 100 , 000 miles runs well..kick…

Customer Question
1990 MB 300 TE Wagon...
1990 MB 300 TE Wagon - AC does not work, heater and fan works, has 100,000 miles runs well. AC charge has been checked and found to be OK. Compressor clutch will not kick in by itself. It will come on when I jumper the AC compressor and cool the car, but will not run on its own. Have checked voltage at the low pressure switch, and it has 12 volts on both sides when the key is on. Any ideas what the problem is??
Submitted: 8 years ago.Category: Mercedes
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Answered in 4 hours by:
6/29/2010
Mercedes Mechanic: Marty, Mercedes Technician replied 8 years ago
Marty
Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 55,290
Experience: Bosch Certified Master Tech. Over 35 years experience.
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Sorry I've been so busy at work I've fallen behind my questions. I think you need to try a few things. First I'd like you to check the wire from the relay to the compressor. You need to be careful though and make sure you get the correct wire. Terminal #22 in the connector should be your a/c clutch and terminal #21 should be battery voltage. Jump the two terminals in the connector and see if your a/c clutch clicks on. If the wire proves to be good all the way to the clutch next I would jump the clutch and measure the signal from the speed sensor with the compressor running. You should measure approximately 0.3 volts AC on terminals 5 and 6 at the relay. Let me know what happens.

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