Originally Posted by markwb
A reputable A/C service mechanic will first check the R134a state of charge. They usually connect a roughing pump to the A/C system to pump it down to hard vacum, then do a drop test under vacum. This also removes any non-condensable gases from the system. Once strenght & tightness (air tight integrity) of the system is established, they should re-fill with a specified amount of compressor oil & refrigerant R134a.
correct. when i worked at pepboys, we used to do an A/C system performance check for $20 or $25.. plus the cost of leak detecting dye. We would pull a vacuum, look for leaks and check the general performance of the whole system and give an overview of functionality