I suspect that heated air is getting in and mixing with the cooled air. (The a/c system seems fine; condenser works, plenty of charge.) This car does not have the monovalve, the failure of which would have explained this failure on other cars. I've searched on here and can't figure out how this mixture works on this car, or where to find the valve or other device that controls it. Thanks in advance for help!

The car is a 1991, though I doubt this matters...