I converted my 87 240 Wagon to R134-A a few months ago and I have been having some issues recently as the outside temp has gotten warmer. I changed out the compressor, dryer, and expansion valve when I did the retrofit and I did a flush and vacuum of the system and installed 3 cans of r134-a. I also put in the recommended amount of the new oil that came with the compressor. It worked OK after the conversion (not great) but I lived with it for a few months. Now the AC will run cool for 5-10 minutes when I first start the car in the morning, then it gradually warms up until it is not providing any cooling. I have added 3 cans of R134-A in the last week and no improvement. One of the cans had UV leak dye and I did not see any leaks. The expansion valve has frost on the outside of it. The low pressure gage reads around 20 psi when I first start the car and drops to near 0 psi after running for 5-10 minutes.

Any ideas of what to try to get cooling again would be appreciated.