I have a friend that has a 1977 Pontiac Can Am that has an a/c problem. When you put the a/c control on Max a/c, the blower stops working, and also when you put the fan speed on high, it also stops blowing. I have replaced the blower relay, but still the same. I can't seem to find a wiring diagram for the can am. Any suggestions? Ballroom

 

Try the blower motor resistor. Sounds like that is the issue