A/c issue
 

Hello all, in my attempt to gain air conditioning after my system gradually petered out I have replaced the compressor, the control unit and the relay. (I’m better at throwing parts at a problem than diagnosing Lol). The system is basically empty and thoroughly vacuumed, and I cannot get the clutch to come on even after jumping the pressure switch. I was wondering if there is a way I can wire the compressor directly to the battery in order to get the clutch to come on in order to fill it up. there are four wires in that pigtail from the compressor, and if it is possible to connect directly to the battery, I don’t know which wires to connect…. Any help on this overall situation is welcome! Thanks! (1987 300sdl)

You dont want compressor to run until you have some refrigerant in it. Charge into vacuum via low side port. Once some freon is in system, at enough pressure the compressor should come on, allowing you to add a little more if needed. Do you have a way to weigh how much you add?

I have a gauge to measure pressure but not the actual quantity. I have no other way to put it in but with 12 ounce cans.

Calculate how may you need to add and add it. Once pressure in system compressor should pull in.

Are your hoses fittings R134 or R12 style? If they are the R-12 style, or just plain old, you should replace the barrier hi/lo hoses with new and the drier as well. Was not mentioned if you had done that. Given your scope of work and investment thus far, would be worth doing it so it will last another decade w/o issue.

When you draw it into vacuum and fill, plus the can pressure, you should be able to get to 20-25psi without the compressor. I believe the pressure switch on the compressor will not engage until near 20psi is detected. From there the comp will aid in filling to spec depending on the gas you are using.

Ok, what you are doing is not wise, but, if the pressure switch is bypassed, and the clutch still won’t engage, either the clutch is bad, there is another safety holding out the clutch, or there is a voltage issue.

You need to test where the issue lies. A volt meter to measure voltage, you should have 12v at the clutch pins. If not, move back to the pressure switch, then check the fuses and see where the problem is.

Good procedure with ac is, first pressure test the system with around 150psi of nitrogen and verify a leak free system, then evacuate the system, and then immediately fill the system with refrigerant. Start the system up, and adjust charge to the correct volume.