I have a 1992 W140 300SD. My A/C compressor is not turning. IN the past (1987 300SDL W126) my A/C compressor was engaged 100% of the time, except in economy mode.

I believe that my system is low, I will verify with my gauges but If I need to what pins do I jumper to bypass the low pressure switch?

Is this onthe receiver drier as on the older MBZ? I did find a 3 connector plug. Low pressure and high pressure?

Also is there another procedure to charge/top up a A/C system?

thanks in advance
Steve