If you do have climate control, as VS Tech questioned, on a car that has not run since 1998, you may want to consider blocking off the green vacuum line and making your heater run on an on-off basis. W123 climate controls are notoriously expensive and difficult to get running. The evil servo is no doubt bad, and that alone is almost a thousand dollars.

I live in the tropics and need no heat, so I have my 300D set up so when I push the defrost button I get air conditioning. Works for me.

Richard