why does my air conditioner work really good sometimes? on 1991 Buick Park Avenue

while driving it will blow really cool air for about an hour and then it starts blowing hot

Asked by for the 1991 Buick Park Avenue
My 99 Park Avenue was doing this a few weeks ago. It was weird, because sometime it was just hot air, and sometimes it was cold air from the passenger side vents, and hot on the driver's side (at the same time). The culprit was low coolant.
check mechanical linkage under bottom panel ..far right side just up from floor
1 more answer
faulty relay ..under hood fuse panel