R129 500SL . Hot air from side vents , cold air from center vents with AC on

[ytech15]

I checked the mono valve and it seemed fine getting 12V DC at the connector. I replaced with a known good (thinking the internal seals may be bad)- resolved the issue for 24HR . Now the issue is back. Am I facing corrupt actuators? A faulty control unit?

[sixto]

In other models it’s a symptom of low refrigerant fill.

Sixto
98 E320s sedan and wagon
02 C320 wagon