My A/C has been ill effective since last winter But when the lovely heat wave (in michigan its hot anyways lol for us..) started i wanted to fix it. So i vacuumed out the system (got the air out and it held a vacuum of 18psi no problems. Then i filled it with UV dye refrigerant cause i knew there was a leak....In less then 10 days the system was TOTALY empty back to 0psi....im no expert but thats def. a major leak. However i have checked all over the engine bay/underside/passenger compartment....and cant find anything. Seems that peope have problems with the evaporator? which is located by passenger foot well/theres a drain plug which u normaly c the dye but i couldnt see anything. Any ideas on where else it could be leaking or maybe is it possible the refigerant gets out but the dye doesnt? im not much of eexpert on AC systems but i do have a old but nice set of high and low pressure gauges. I just filled the system last night to about 220psi on the high side and i think low was 50"not positive though" and the air temp was 80. final static pressure was 90 which seemed slightly high so i may have over filled it but just sitting over night i went back this morning and hooked up the gauges and its down to 150psi on the high side (with the system running of course). Thnx for any advice....

P.S gonna be a freshman at MTU so everyone says i shouldnt fix it cause i wont need it but i NEED it now lol.

 

Truck: 99 QC 4x4 360

 

have you checked for leaks at the condencer core and compressor ? also check line fittings,they have o ring seals that can leak.