A/C Kick On with Vent

[Cornerman]

'99 B3000
5-speed
V6

My A/C compressor kicks on when I put my selector on combo high/low vent. I don't think this was always happening.

The high(face) vent alone selection is normal (no A/C), and the low vent (feet) alone selection is fine. Only the high/low vent combination setting kicks on the compressor. You can see the compressor turning when it clutches in, and of course, feel the power loss.

Just to be clear, if I am in Max, A/C, Defrost, or Defrost/Feet Combination, the compressor kicks on as it should. The only setting that seems different than any other automatic a/c compressor is the high/low combination vent.

Any ideas?

Cornerman