My husband bought something that sounds similar at our local parts store - comes in a pressurized can - and he recharged the system in our 94 GMC Jimmy - hope this helps !
The AC recharge port on a 2004 GMC envoy is on the low pressure connection. It is the larger of two hoses near the firewall.
Using the proper type of freon and a gauge, connect to the low side ac port. With the engine running and the ac on high, add freon till the gauge shows full.
take it to a dealer.
The air pump or smog pump on a 99 GMC Jimmy is located right behind the bumper, below the radiator, and on the passenger side.
91 will have r-12 freon but can be converted to r-134a easily
in the low pressure side
If the system is empty you have a leak. If you try to recharge it yourself it won't last for long. Take it to a AC specialist and get it over with. If you must give it a try go to your local auto parts store and purchase a recharge kit. The kit will come with directions. Remember it is illegal to release refrigerant into the atmosphere.
How do i Recharge AC Unit for a 1998 Dodge Stratus
you dont nid to change it is the same a/c is controled by the front control turn front on and turn rear on
It should be located on the passenger side near the firewall.
it is on the fire wall about half way across it. it is next to the powerr block