on the passenger side close to the firewall on the receiver dryer
It should be 134A, look at the fittings, if there are threads on the outside it's R-12. If they look like air hose quick connects it' 134A
The proper charging kit for a 1994 Chevy s-10 is a 134a - NOT a R-12. You can purchase this charging kit from most automotive stores.
The high and low pressure service fittings are different between r-12 and r-134a systems. To attach service equipment to a r-12 system the equipment would be threaded on to the service ports. The r-134a service ports have a snap on quick disconnect fitting.
YES--now days 134a coolant is used in all systems.
If your system is totally empty you will use 28 oz of R-134a. If you are topping off the system you should fill to the correct PSI level. You can find a Pressure Chart on the link below. Look on the Diagrams and Specs then the R-134a System Pressure Chart.