No A/C

I have a 94 that i'm having ac issuses with. The problem is the a/c compressor will not turn on. I cannot get a reading from the port on the low side of the a/c line. I can however get the compressor to cycle after shorting out the cycling swtich.
Being I cannot get a reading from that port I emptyed the system, installed a new 134a PORT and a new cyclying switch then proceeded to put in 1 can of stop leak and 2 regular cans. Everything appeared to go well the a/c compressor started cycling and cooling the car fine. It worked for 1 day and stopped working again. (ie. The compressor stoped cyclying) I still cannot get a reading from my gauge to tell exactly how much pressure is in the system. The port I replaced is on the low side a/c line between the accumulator and condensor.
I can hook my gauge up to my 2000 blazer and it reads 35 pounds so I know my gauge is fine. What am I overlooking????

You did not mention evacuating the system (using a vacuum pump) of air and moisture before you refilled it with R134. There are good reasons to do this. First, it allows you to check for leaks. If the system will not hold a vacuum, there's a leak and the system will not hold the R134 either. Also you need to get air and mosture out of the system that entered while the system was open. While the system is open, it's usually a good idea to replace the O-Tube and the accumulator also.

I had a leak once around the O-Ring on the pressure cycling switch on the accumulator. Fortunately, I caught it with the vacuum pump before refilling the system.

If you want to do a super job on your A/C, then after the system is empty and open, flush it out thoroughlywith A/C flushing solution, replace accumulator and O-Tube, add the correct amount and type of oil, close the system back up and then evacuate at least 1 hour and then refill. Yes I know it's a lot of work to do all this.

Hi, I did not vacuum the system out due to not owning one yet. However the system did seem to have plenty in when discharged. My biggest problem right now is not knowing how much pressure is in the system. Why would you not get a reading from the 134 lowside valve. That was the main reason for the discharge in the fist place because I thought it was a faulty valve and replaced it. I guess it is possible to have a leak but I need a pressure reading to know where go from here don't you agree.. Don

Sounds like for some reason your gauge plunger is not opening the Schrader valve in your adapter on the low side. If the gauge works on another vehicle, I would suspect the adapter or Schrader valve is bad. I had a bad adapter in a new (never opened) R134 conversion kit the other day that had a broken pin in the Schrader valve!! They must be making them in Mexico now days.

This is what stumps me.. That is the main reason why I put a new valve in because knowing the gauge works on another vechicle. Unless there making crappy valves!!!!!! Thanks for giving the proper name for that valve I didn't know what to call it...I can't see any reason why it shouldn't give a pressure reading. The old one worked when I added a can to the system last year. Now the old and new one won't work. I'm going to buy another gauge today but for some reason I have this feeling it won't read either... Don

Have you tried checking the high pressure port? When the compressor is not running, both low and high pressure ports should read the same - about 100 PSI on a hot day. If you get pressure on the high port and none on the low port, then the system is charged and the low port is not reading correctly. If there is no high port pressure then the system is not charged, or both ports are bad. This all assumes the gauges are good.