624. Adding refrigerant to car A/C

Surprise, these instructions aren't always correct! So were the instructions on the AC PRO Refrigerant I added to my 2003 Subaru. The instructions stated to not undercharge or overcharge and to ensure the final pressure lies within the range on the gage. Well, it never made it to that range on the first can. So I bought a refill and same thing was happening. Turns out after calling their hot line that some cars have an expansion valve on the system (like on your hot water heater) to relieve pressure too high for the car's A/C design. The Subaru was one of them obviously. So, the atmosphere got half of what I tried to put in -- thankfully, it is only clean synthetic refrigerant now. Thus, beware of AC PRO instructions or any refrigerant instructions that don't tell you to STOP adding when pressure stabilizes. Live and learn. Next time I'll consult the Subaru manuals too.