I bought a '79 300SD in Jan. and was told the A/C compressor needed to be replaced. I replaced the a/c compressor and charged it up and it cools fine (42 F). The problem is it doesn't shut off, even with the temperature dial set at 85 F. Is there a thermostat or sending unit or something that might be out?
Also, the heater hasn't worked since I've had it.
Any suggestions?

Fix your heater. The system maintains the requested temperature by mixing warm and cold air, not by cycling the compressor off and on.

On a 79SD, the AC compressor engages anytime the climate control is operating.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Thanks for the help. I would have gone nuts chasing that down!