I had to open my AC lines during an engine swap. I replaced the O rings that I disturbed and replaced the dryer. I have an appointment to recharge the system. Is there anything else I should do?

 

Did you lubricate the 'o' rings with compressor oil before assembly?

 

No I used O ring lube.

 

Had my AC evacuated and charged. It lasted for a day. Went back and put leak dye in the system and charged the system again. Found dye coming out of the low port. Stopped that leak and recharged. No more leak at the low port and no leak that I can see anywhere else, lost my charge once again. Anyone else have this problem?

 

Down in one day? That is big enough leak that it shouldn't be hard to find.

I assume you are inspecting with an UV light and cannot find any trace of the dye. Look behind the compressor clutch best you can. Seal failure is common there. Keep looking at all the connections. Look for signs of oil at a connection. The high pressure side has more probable locations.

Worst case was my evaporator core leak. No UV dye found anywhere by two different AC shops. Can't see dye in there. I found it by sticking a 'sniffer' down the dash AC vent. Couldn't detect it on anything other than low fan. More air diffused the R134a too much to detect.

 

Yup. Turns out I had a leak in one of my AC lines. The lower one on the rad was the culprit.

You can get a dye refrigerant and a black light to help hunt it down. You'll always see some dye at the schrader valve in the fill port since thats where it goes in. You can also try charging it up and listening around for the leak...takes a while but worked in my case.