helmjon did you add all your R134 with the machine or did you use the little refill kits?? Most refill kits come premixed with oil, the problem with this is that when your A/C leaks over time it saves the oil but the R134 gets discharged.. Also most components will come pre charged with oil but not r134.. With too much oil in there it will cause the high pressure switch to kill the system.. I forgot what the kill pressure is but you might be able to find it somewhere..

 

Too much lubricating oil can cause the same symptoms as low refrigerant charge

 

Your Durango has rear air in it. It should take 2.0 lbs. of R134A Freon and not 1.75 lbs. That is the reason that it cycles after going down the road a few miles. If your mechanic is using the machine to charge the system, tell him to put in 2.25 lbs., like I said before, there is around .25-.45 of freon left in those lines that he disconnects from your vehicle. The reason I know that is because I did it myself to check it and you can verify it, is to tell him to do a recovery on his A/C Machine after it is disconnected from the vehicle. You will see that he will recover around .25 to .45 lbs. of freon in the lines alone. So Basically, when you recovered 1.75 lbs. and he might have used 2.0 lbs. like the machine says, but that last .25 is still in the lines of the machine.

 

You are correct, that is why when shops do A/C work with a recovery machine, they also recover a certain amount of oil out of the system. A/C refill cans do not all contain oil in them, they have to be marked on the cans that say they contain oil. A person can go and get regular R134A freon without oil in it, just have to read the cans before buying them.