On my 1987 300D Turbo, unless the climate control wheel is at max cooling after a few minutes (at 22 degree stting) heat starts blowing out of all vents. By turning the wheel back to max cooling cold air will blow out all vents. Any suggestions as to what might be wrong.

Could be:
Monovalve leaking
Climate Unit not functioning right
Interior ambient temp sensor not functioning right and reading off incorrect interior temps

Monovalve is most likely so start there.

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If the monovalve was at fault, the problem would occur in the "Max Cooling" setting. There is nothing in the presented symptoms that suggests a problem with the monovalve itself.

Center vents pointed up at ceiling where interior temperature sensor resides next to dome light. Once you chill it down, it turns on the heat to warm itself back up.

Solution: Re-aim center vents straight into car.

Thanks for all the help. How dumb can I be - redirecting the center vents so cold air does not hit the the heat sensor did the trick. Thanks again.

On the plus side, ya gotta love the level of effort and complexity on that fix!