Saturn ac

You need to evacuate the system first, then using a vacuum pump get all the air out. Make sure the system holds vacuum and then put your 134 in. The vacuum will draw enough in to start the compressor. Correct amount of 134 is 24oz. You will never know how much is in your system if you don't start empty.

Steve

Steve Tomaszewski N2PTJ

I believe that the three wire pressure switch gives a linear voltage output proportional to pressure. goes to the BCM. first make sure that you didn't loose oil from the sealed system. If there is any chance of an oil leak - you will see oily coated A/C hoses or fittings - you must replace the oil with the correct type (PAG). A UV Dye tracer will help you find any leaks.

Generally, you take the gauge / hose adaptor and connect to the LOW side of the compressor. Bleed out any air in the hoses by cracking the can tap valve slightly before making connection to the car. Open the can tap and let the R-134 feed into the system. It's a slow process as the liquid in the can has to boil off to charge the system. Some folks are tempted to invert the can and feed liquid instead of gas. This is really bad to do as it washes lubricant from the compressor and can cause problems when trying to start the compressor. Normal pressure with the compressor running is 45psi. You should be able to get enough pressure by just connecting a can to enable the compressor to run. May need to sit a few minutes to equalize and the computer to register. Also try putting the selector switch to defrost which should force the system on.