Does the A/C compressor turn on when you set A/C on the temp controls?
There must be a minimum pressure for the compressor to even power-up its clutch (a safety against running it unlubricated)
You may wanna check that your hot-cold slider goes all the way to the "cold" mark (that year has a vacuum operated heater valve - not getting the slider all the way to cold still leaves hot-coolant circulating through your heater core -- the adjustment for travel is the cable seen above your passenger's left foot)
Once you've verified the proper travel in that slider - with the engine running at idle (generating vacuum) check under the hood to ensure that the vacuum valve is at least moving (you'll be able to see the actuator move the valve arm -- ithe heater valve's near the firewall kinda above the starter hanging on the heater hoses there) -- if you don't see motion check for vacuum on the line and proper operation of the vacuum actuator on the valve itself..
NOW with the thing out of the heating mode - you may wanna check the fill level of your sysem -- if it's factory, then you're still running R12 (hard to get cheap, thank congress and the EPA), since the minimum sale size for service is 30# and then only to licensed professionals, you may wanna consider a DIY job to convert to the not as regulated R134...
... kits for that conversion are at most aftermarket places -- ensure that, if you do convert, that the kit you purchase is 100% tollerant of your old system's contents - you should replace the dryer and all seals (I believe that most of the early conversion litterature recommended replacing every non-metalic part, then flushing the system befroe drawing a wicked-strong vacuum on the system to clear it all out), but I've seen favorable results with just a kit that directly mentions it's compatibility with previous oil and freon types...