so i have finally decided to try and fix the ac in our truck just in time for the heat on the way, i have a leak somewhere that i can seem to be able to find it tends to go from full to basically empty in about 2 or 3 days of use i have ran some uv dye through the system drove it for about 2 days and during that time the ac had given out and still unable to find out were the leak might be i had bought an el cheapo sniffer freon sniffer from amazon ran it around the system and wasnt able to find out where it was leaking ran it for about 30m tonight nothing from sniffer or uv light. any help would be appreciated i hope im just overlooking the obvious.

 

Evaporator core..... Or the front compressor seal.

 

If your leak detector is decent it may be able to pick up a leak coming out of your vents. (with fan and a/c off) This would confirm an evaporator leak.

 

it can be difficult. You could also try charging the system...running the system to create high side pressure...and spray soap solution on the big components and seals. if the leak is big enough bubbles will form. can't test the low side as its all covered. let the soap solution dry before you use the electronic sniffer as it can cause false hits...you don't want water in the sniffer.
when you use the sniffer...go slowly, refrigerant is heavier than air so leak test under lines, seal and components

common parts to fail are seals...they deteriorate, condensers get hit with road debris

never use a system sealer.