Auto Air Conditioning & Heater Repair: 95 Chevy Tahoe Low Pressure Valve, r 134a, chevy tahoe

Question
Bought a can of R-134a "All-In-One" recharging can at the local auto parts store to recharge the a/c unit.  Need to know which of the two valves is which.  There is one near the compressor and one near the firewall cannister.  Which one do I hook the can to?  Thanks for helping an automotive repair bozo.  

Answer
Hi rick, the service valve is at the accumulator.check your hose fitting which should be the same as the accumulator.Male to female connectors. The accumulator is by the firewall- low side pressure is the service side to add freon.If your still not sure ask for help.

good luck , davidt