Hissing from AC compressor ?!
 

08 g35xs sedan

wats up guys, i took my car to the mechanic the other to see what was wrong with my AC because after recharging it, in like 3 days, it was blowing hot air. when he was putting the dye in the system we started to hear a hissing sound coming from the compressor but didnt see any dye with the black light on the compressor. i havent checked the compressor to see if it has dye around the outside now. if i remember correctly the blue gauge on the manifold tool was at -20. and the red gauge was at zero. price for the compressor is 400 new. with laber it comes out to 725. i want to make sure thats were the problem is coming from, before putting in all that money into it. after he heard the hissing coming from the compressor he said i shouldnt add refrigerant because itll come right out.

thanks in advance !

Just refer to the Factory Service Manual, it has detailed troubleshooting for gauge readings. Blue is the low side and red is the high side, I don't usually go off kg/cm2 because it's such a small number and it's more accurate to use the PSI scale on the gauge 20 is almost 300psi, that is normal high side pressure but your low side is nonexistant if it's actually zero on the gauge. Low side should be somewhere around 40-60 psi which is like 2-3 kg/cm2.

Your HVAC tech should know all this stuff... is the compressor cycling properly? Did he pump down the system and recharge with nitrogen? Did he thermal scan the high/low sides for proper temperature changes? Does he suspect (like I do) that you actually have a valve issue?