OK... I'm facing a similar issue with a 96: Always blows hot unless on Max A/C.
Apparently this is almost always related to the blend door. Proper repair requires removal of the dashboard, and the kits and 'how-to's" available involve cutting the air plenum to get to the broken door....
I believe there is a very quick, very simple workaround. The Heater Control Valve (under the hood in the heater hoses going to the heater core) is held open (allows flow to the heater core) by vacuum that it receives when the HVAC system is set to anything EXCEPT Max A/C. When set on Max A/C, there is no vacuum to the HCV, and it closes (recirculates coolant back to the engine, bypassing the heater core).
The workaround: remove the vacuum line from the HCV (and plug it so you don't induce a vacuum leak). This makes the HCV act like it's on Max A/C. This will get you through the hot summer without getting a face full of hot air, and also let you enjoy better fuel economy by not having to run the A/C compressor.
When you need heat, simply put the vacuum line back on the HCV.
Total time for the workaround - about 2 minutes (including the time for finding a golf tee or small bolt to plug the vacuum line). Cost - 1 golf tee or small leftover bolt (2 cents?)