Can someone please tell me what these little red and blue buttons located at the center vents are for?

I assume that the blue one is for cool and red for hot. But how and when to use them?

Is the blue one to be used only when the A/C is on?

If the A/C isn't one, and you press the blue button, does that cause the compressor to kick on?

Just how are they intended to be used? Are they useful?

The manual isn't very helpful.

Thanks,

DieselDawg

__________________
'82 300sd
'92 300sd