Trade it in on a rebuilt one, it's not really repairable at home. Later (post 86, maybe all W124 units) have all electronic components, not the switches on the older units, and don't suffer from broken solder connections.

If the unit is giving you only hot air out the defrost vents or is not switching functions properly (air out the wrong vents), check the fuse first -- if it goes, you get full heat, windshield only, no fan. Replace the fuse, don't just spin it as the aluminum can vanish at the contact point.

If you have power, the vents work right, but the fan is dead, check the strip fuse for the fan (small box next to the fuse box) -- they crack in service and the blower won't run.

If you have only misdirected air, check the servos -- there is a switchover "bar" on the side of the AC box accessable after you remove the glove box (two screws for the catch, 8 "push rivets" -- pull the center up and the rivet base will come out, pull top center down to clear the hook molde into the top, pull liner our). Use a mitivac to test each line, all must hold vac indefinitely.

Converting to a manual control would be a big PITA even if you could get the parts in the USA.

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!