you are low on refrigerant.
get a can of 12 and adjust the charge to 32psi. look at the gauge, the little colored numbers correspond to boiling temp, you want the boiling temp to be above 32°F an easy way to test, is lay your hand on the cool suction line, when it flashes to the feel of a cold can of soda, you are pretty close to the correct charge. also, the sight glass on the receiver drier should flash clear of bubbles when you are full.
John

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!