Where is the most likely spot that an AC will leak?
The car (92 Z28) was converted to 134A. It was doing great for a month, but then after I finished hooking up the fan controller, the compressor started to cycle. So I hooked up my guages.
Engine off, 85 low side 75 high side. Compressor on, dipped down to 20/150.
I added about 20 ounces of a left over bottle i had. He jumped to about 25/190 compressor on. 20 ounces seems like a lot for such a small increase.

 

Possible leak locations.

Evaporator inside heater box
Any rubber part of a hose or where the metal crimps around the rubber hose
Any o-ring/seal connection where a hose connects to another component
AC compressor (body joints, shaft seal etc)

You could use a freon sniffer to try and pinpoint a leak. When I repair ac systems, with all the freon out of the system, I charge the system with nitrogen then use a soapy water solution to spray all possible leak locations and look for bubbles but even then leaks at the evaporator can't be seen. A freon sniffer at a dash vent can usually detect a leak from there.

 

I agree with above. Mine always seemed to leak in the compressor body with the R4 compressors, or the sides of the condenser.

I know it's not recommended, because it supposedly adds contaminates into the system, but if it's totally empty I have added 80 psi of shop air into the system then sprayed everything with dish soap and water mixture and look for bubbles. I guess you could try it without the shop air and see if the freon will make bubbles.

 

Here are a few pics of the dye. The first is behind the compressor, and the other 2 on the dryer.
The dryer might be normal. I bet people in the past didnt cover up the connector when plugging/unplugging, and stuff just went everywhere.
I dunno if whats running down the compressor is normal though.

I dont know how to get access to the condenser. Its pretty crowded down there.