AC comp.
 

1990 mb 300sel no power to AC comp. Replaced comp. clutch went bad.
This modle has a mass relay that is fuel pump relay as well as ac clutch cut
out. Low pressure switch ok freon charge ok. I need help on this one
so i dont become a parts replacer. How do i read codes ? I have michal on.
demand but not much help. I work for a MB dealer for 6.5 years then started my own
shop in 1983 I love MBs but not this one
Duane R. Phillips

I would check the "ON" signal to the low pressure switch. This wire comes from the pushbutton, goes through the low pressure switch then goes to the MAS unit. Onces it tells it to energize, the mass unit does the rest.

I have replaced many MAS units for this reason.