My A/C clutch does not engage in my 1982 300. I'm not sure if it is due to low freon or an electrical problem. I measure 9 volts at the connector on the clutch when the A/C is turned on. This seems low. Can I apply 12 volts directly to the two terminals on the clutch to see if it engages?

If I short the terminals on the high pressure swicth, should it engage?

Yes you can put 12 on the terminals. IF you bride the low pressure switch and the ETR is working, the compressor should come on assuming all of the electrical system is OK.

Well, I shorted the pressure switch and nothing happens. Also, now when I measure the two wires going to the clutch I read 0 volts. So now, it looks like there is nothing going to the clutch. I haven't tried applying 12 volts directly to the clutch. Are the two connectors polarized? If so, which is which?