Three things to check.

1) Monovalve. You should be able to feal this click when you go from heat to AC. But just because it clicks it doesnt mean its OK. You may also have a bad diaphram. The only way I know to tell is to pull the 4 screws and look. This is a 20 min job and about $30.00 worth of parts for a diaphram replacement.

2) AC Charge. Are you running R12 or R134. R12 will be colder than R134. Nothing you can do except go back to R12, which will mean flush and new oil unless you know Ester oil was used.

3) AC undercharge. This is most likely your problem. Have an assistent that you trust put the car in park and hold 2000 RPM with doors and windows open and AC on. You should see no bubles or very few bubbles in the sight glass. Make sure the glass is clean and the compressor is running. The sight glass can be cleaned with a pencile eraser.

John Roncallo