bates2121

I have a 1998 Chevy K1500 6.5L turbo diesel and my problem is that the a/c heat vent control isn't working properly. I have spent 2 full days trying to fix it myself but with no luck. The vents wont change from floor to any other position the **** twist but no effect and the a/c and recirc air buttons don't engage or light up. What I've tried is to replace the control unit but it made no difference and to check the mode door motor, works but only when the fan/blower is turned off so it will change the vents but as soon as you put the blower on the vents go back to floor, also I bypassed the control unit and hot wired the a/c to see if it still worked and with the blower going and the control unit bypassed the a/c blows ice cold. so my only guess is a relay. This is the hvac control unit with 3 twist ***** and a button for a/c and a button for recirculating air. I replaced the control unit when I first got the truck 2 years ago b/c the controls would stay on the windshield vents and wouldn't change to any of the other vents and the a/c button wouldn't light up or engage the a/c. Replacing the control unit fix it all. But now it is something different any help or input you can give is well appreciated.

Thank you
Pvt Bates

EinST

It sounds like a grounding issue. The ground side of the blower is tied to the ground side of the air door actuators. If there's sufficient resistance between the grounding wire and the actual chassis ground, the blower will actually supply some positive voltage to the shared ground side. Measure the resistance (not just continuity) between BLK wires at electrical connectors and known chassis ground.

stuhomi

Did That Solve The Problem Bates ? I Would Like To Know Because I Am Going Through The Same Problem. Very Frustrating !!I Replaced Condensor, Compressor, Orfice, Dryer, High And Low Side Switches, Manifold And Ac Heater Switches. I Started The Truck And Light Came On, I Charged The System And Let It Run For A Litle Bit With Cold Air. Turned Off, Put The Grill Back On , Started Up The Truck Again And Now, All That Is Happening Is Hot Air At The Feet, Compressor Not Running And No Light At Switch. Called The Dealer And They Said To Change The Head Unit. I Replaced With New One And Still Same Thing. Gotta Be Something Simple. Just Don't Know What Else To Try.