Symptoms: gradual loss of a/c

steps taken: replaced expansion valve.
anti-freeze switch and pressure switches replaced last year.
put 24oz of R12 in system.

a/c clutch will not engage. Tried jumping freeze-switch and pressure-switch. No difference.
Freeze switch has 4.5 vdc one side and 0 vdc the other.
Together they have 10 vdc. Pressure switch has 12 vdc. Clutch is not frozen.

 

When you say gradual loss, do you mean that it's starting to blow hot air? If so, have you checked for leaks by putting the neon dye in the car?

 

The only leak was at the expansion valve, which we replaced. We are puzzled as to why we cannot get the compressor clutch to engage.

 

Sounds like the relay in the head unit is a possibility. try just feeding 12v to the freeze switch (& therefore to the clutch)- does it work then ? if yes you need the head unit relay fix.

Alan

 

I don't have the WSM here, but the sticker on my car says 33 oz no rear air, 37 with. At best you are 9 ozs low. Yes, jumping the low press switch should do it so Additionally, the voltages you are getting suggest Alan's course.