1999 S320:

Air conditioning works fine 75% of the time. Will randomly stop blowing out the center vents and shift up to defrost vents. I can hear the center vents closing.

My mechanic got the following error codes from the climate control system:
B1234-sun sensor B32
B1423-switch valve block y11
B1419-electromagnetic
B1436-rear a/c shut off

Then he cleared the codes. B1423 came back and would not reset.

Any ideas on what the next move should be and what parts will cost?

Thank you!