Bi-level center vents blows no heat
 

Have a 91 300E and I noticed a wired thing. When I set the climate control to 85 (it's cold in Chicago) and press one of the blower buttons the blower blows heat on the winshield, by the foot and the two side vents but not the center vents. When I press the next button the heat blows in the same directions. For some reason the heat does not come from the bi-level center vents (I remember it used to when the A/C is on). Is there any other way to get heat from the center vents or is there a problem with the dampers.

Check your owner's manual. The center vents are not operational in "heater" mode...