You can test the auxilliary pump pretty easily by jumping 12 volts from the battery directly to the pump and see if you can hear it running. It doesn't sound like a bad pump to me though. However, if the pump seizes, it can take out the climate control amplifier. Perhaps this combination is the source of your problems.

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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