I am trying to recharge the A/C on my '91 3.1 RS.I have a Robinair electric vacuum pump and have it connected as follows.Low side going to low side in manifold gauge,High side going to the vacuum pump and Yellow line from gauges going to can of R-134a.I used 3 cans of refrigerant and the compressor never engaged whatsoever.I can jumper the pressure switch and the compressor will engage.If I used 3 cans,where did they go?Did the pump just vacuum it all out?I know the shop manual shows how to charge and evacuate.I can only see two service ports on the car.One is on the condenser and the other(a Schrader valve)is near the condenser on another line.That line is going up front to the evaporator.Are these the only two on the car?I don't see any near the compressor.Any sugesstions?

Ken

 

No more than 2 lbs or two cans.

 

Unless you have a 4 port manifold, your vacuum pump should not be hooked up during charging. That's probably where your refrigerant went.

If you can post a pic, I can help you identify your ports.

Hook your vac pump to yellow hose.
Hook the blue hose to low side.
Hook the red hose to high side.

turn on vac pump, open vac pump valve, then open both manifold valves. This will pull vacuum on the hi and low side...it's more effective than pulling vac on one side alone. Watch your low side gauge to pull into vacuum. When it looks like it's bottomed out, check your watch and let it run at LEAST another half hour. When that's done, shut off manifold valves, shut off vac pump valve, then shut off vac pump. Do not shut off vac pump until all valves are closed, because if you do, there is the possibility that the vacuum in your ac could suck nasty dirty *** oil from the vac pump into the system (this=bad). Leave everything sit for 5-10 minutes, and look at the low side gauged. It should still be showing the same amount of vacuum as when you shut off the vac pump. If it has decreased, you have a leak, or have not yet got all the moisture out of the system. If it held, move on to charging.

Disconnect vac pump, and hook up your charging apparatus. With manifold valves still closed, open the refrigerant supply valve. then loosen the fitting for the yellow hose at the manifold until you hear gas hissing for one second. This is to purge the air from the hose line that got in when moving the line from the vac pump to refrig supply. If you're low side port is on the side of the accumulator, you can charge with liquid (can upside down). If the port is not on the accumulator, it is best to charge with gas (can right side up). You want to put in 2 cans. You want to do this with the ac running on normal, blower on hi.

After you have 2 cans in, set the ac to max, blower to high, and put a thermometer in the middle dash vents. let it run 5 minutes to stabilize. Note the temperature it stabilizes at. Hook up your third can, and try to add about 4 ounces (1/4 can). You probably don't have a scale, so just use your judgement and estimate. After adding that 1/4 can, wait several minutes for the thermometer to stabilize, and check your temperature again. If it's lower than when you started, add another 1/4 can, wait another 5 minutes, and check again.

The idea here is to keep adding refrigerant as long as it keeps improving performance. As soon as you notice temp coming up, stop, you're no longer improving. Do not put in more than 3 cans. More than 3 will degrade performance, more than 4 will kill the compressor

 

Don't use more than 75-85% of the original R12 charge you will cause damage to your system!!!! R134 requires less refrigerant than R12 to perform correctly! I'm running 2lbs in my car and it's blowing 39 degrees.