Auto Air Conditioning & Heater Repair: AC pressure, dodge grand caravan, red angel

Question
I have 94 Dodge Grand Caravan. I used to take the car to have AC service every six months because the system has slow leak. No shop can find where the leak is after they add the dye etc. Recently, I give up to take it to the shop and just add those 12 oz can refrigerant on my own. I bought high/low gauge to check pressure as well. The compressor model of this car is 10PA 17K, and the oil that I use is PAG46. I added 2-3 cans of 12oz refrigerant on May 10, and total of 6oz PAG46 oil that include RED ANGEL AC Stop Leak and the AC is still cold now. This was the first time I did it myself. It is very hard to tell when the can is completely empty. How many minutes will the can be completely empty? I think I almost empty 3 cans of 12 oz refrigerant. With the engine idle & AC on MAX, the LO port pressure reading is constantly going up and down between 16 psi to 41 psi when the weather is about 75F around my area, and I can't get any reading from the HI port. Do I need to keep certain RPM in order to do the reading? Those pressure chart refers to ambient temperature. Does it meant that the termerature around the compressor under the hood or the temperature from the weatherman. The AC is cold and working now. It is colder when I drive on highway when RPM is higher. Is RED ANGEL AC STOP LEAK good? I don't know if I need to check further due to the LOW pressure reading constantly going up & down between 16-41 psi and I can't obtain any reading from High pressure port when the engine is idle (Not sure what is the RPM at idle). The funny thing is that is AC is cold now even with the pressure reading described above. I notice that it will take a little bit longer to get cold for city drive not like highway. Someone suggested that the fluctuating pressure MAY indicate a plugged or dirty expansion valve. Should I take the car to evacuate and recharge again to clear plugged or dirty expansion valve if this could be the case. I am not sure. Any opinion with suggested resolution could be appreciated. Thanks you.

Answer
Hi Woodman


You have few  questions.  Pressures are good for your area they will move up and down especially if if is getting cold.  Stop leak is never good for the compressor and will not work on any leaks that I have ever seen.  Have someone check your evaporator very common for leaks of this year van.