Newb AC question
 

1990 300E, The AC appears to do nothing at all. The clutch does not engage at all. Where do i start the testing? Is there a way to provide needed voltage to the compressor to see if it works? Thanks for any help

Get a set of gauges and see if there is any refidgerent in the system. If it is low, the compressor won't run. You can jump the psi switch to get the compressor to run.

Ya dont do that for long youll burn it up. Look up ps2cho's threads as he has rebuilt his A/C system. Remember charging is a engine running process and starts at idle till compressor engages and goes to 2000 rpms until low side is above 35 psi.

Hook gauges up and add freon with it off if it's so low the compressor won't engage. Then it will engage and you won't burn it up. Add 1 oz of oil to make up for losses- 150 pag (R134a), or 1 oz mineral for R12. Don't forget to bleed the lines of the gauges as you don't want any NCG's in the system(Non condensable gases- contaminations).