Auto Air Conditioning & Heater Repair: A/C MIDDLE VENTS, chevy suburban, climate control

Question
97 Chevy Suburban - no air flow from middle a/c vents while in a/c mode; however it does blow from underneath and above. All air vents work BUT the middle vents in a/c mode.

Answer
Steve,

 Your mode door selector is stuck on default for defrost and floor.  


1.  Try to disconnect and reconnect the battery.  This will solve logic locks in the climate control head.

2.  If you have a multi-meter and know how to use it measure voltage on the brown wire with key on engine off.  It should be very close to 12.  If there is no voltage on that wire check the splice as this is the power supply for all three motors.  If there is voltage on the brown wire then check for ground at the black wire.  If you are good on Bplus and ground its time to check the final wire which is the control signal and is regulated 12v from the climate control head, the white one.  Put the A/C centre vent selection on and you should have close to 12V on the white wire, brown wire and ground on the black.  If you have all those inputs then you most likely have a defective climate control head.  Its not uncommon, but used ones are plentiful.

3.  If you don't have a multimeter or don't know how to use it its a guessing game at this point unfortunately.  Mode door actuators and climate control heads are quite common.  Its a 50-50 shot in the dark or could but something mechanical like the flap stuck.  That would be uncommon.  You could remove the mode door actuator and see if you can manually move the flap but it it very difficult to get at and has an awkward drive on it.  

Hope this is helpful!

Wayne