1989 300 SE / AC Relay trouble
 

Dear friends,

I recently had work done on the above car, ac compressor, ac hoses, driver window motor.

When picking car up, Gas pump relay did not work & replaced.
Immediately after, AC relay did not work & shop has not been able to identify the trouble. AC works when you do a direct bridge without relay, so trouble is related to signal from relay somehow.

Any suggestions ?
Any suggestions for a knowledgeable & reasonable older benz models mechanic in Miami Dade County ?
Thanks very much.
Jorge

Check the fuses for power to that relay.

There should be an A/C compressor speed sensor which is connected from the compressor to the A/C relay - be sure that is connected.

Then check engine coolant temperature sensors to be sure they are connected, one of those is an input to the A/C relay. (If engine is too hot, the A/C will shut off.)

And there should be an engine RPM input to the A/C relay - that would tell the relay that the engine RPMs are fast enough to turn on the A/C compressor.

I got the above from here...
http://www.startekinfo.com/StarTek/outside/12253/program/ETM/ACCfrom86.pdf