If I remember correctly, the supply side comes from the block, and if it's hot, asi should be (engine runs around 90C there), coolant is running through the heater core, reheating the air so it appears that the AC isn't working.

Replace the monovalve insert, it's about $35 I think. Easy job, no coolant drain or anything.

Replace the fan, too -- head pressure will drop quite a bit.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!