Recharge port for 99 blazer is located on the passenger side close to the firewall on the upper side of the silver cylinder tank located there. Trace your a/c hoses from your a/c unit across engine compartment. The larger line connects into the side of this tank. Black cap on port screws off to reveal quick connect recharging port. Smaller line from a/c unit also has a quick connect port with black cap. Single hose recharge kits(134a) will only fit recharge port on side of tank. On the opposite side of tank is the low pressure cut off switch and wiring plug for your a/c unit. This switch prevents a/c unit from coming on if refrigerant pressure is too low.