89 420SEL A/C control problem
 

I am still trying to sort out this control problem. Sometimes the A/C works perfectly normally ... then the next time I fire it up, the compressor does not come on. It seems to work 2/3 of the times that I run the car. Per notes in the Forum about A/C systems on my car production period, when I bridge the contacts on the drier with the conns off and the ignition on, the compressor should "click." Also, one note in re another model of the late 80's said the aux fan should also start at the same time, if the drier connections are shorted for that test?? Are both of these results true for my particular car model??

Thanks, Ben Carter

The compressor is controlled by a computer/relay that needs RPM info to engage the compressor. The aux fans are system pressure controlled to turn on at either16 or 20bar.