Don't repair it till you isolate your problems to it. Have you tried following the troubleshooting procedures/tests in the service manual? If you pull the plug on the ACC Amplifier (I believe that's what it is called - it's a module on the passenger side in the blower motor area) almost all the tests can be run with only a volt-ohmmeter. The tests will rule out sensors, wiring, switches, much of which may come into play even with a manual system. You could have a bad cabin temp sensor or water temp sensor. If you rule all those other things out and isolate your problem to the ACC control unit, then you might resolder or consider going manual. But you're not going to want to go through all that trouble only to find out your problems are in some other part of the system that you'll need to repair anyway.

When I bought my car almost a year ago, the a/c didn't blow very cold, and with the heat on the fan would cycle up to full and blow full heat even with the temp wheel all the way down. Bad monovalve. Repaired that and the whole system has been working wonderfully ever since. For all its supposed faults, when it's right it's a thing of beauty.

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mjk

'84 300SD 119KMi (Liesl der Diesel)
'84 300D 326KMi when the oil left (former parts car)
'82 300SD 253KMi (new parts car)