Mode Actuator Not The Problem

HAVE A 97 SUBURBAN AND THE FLOOR VENT WONT SWITCH FROM FLOOR TO DEFROST VENTS? CHANGED THE MODE ACTUATOR BUT STILL DOES SAME THING? THE MODE ONLY MOVES SO FAR THATS IT? DOESN'T GO FAR ENOUGH TO SWITCH, BUT IF I REACH UNDER I CAN MANUALY HOLD THE BLENDER FLAP TO THE DEFROST VENT :confused: ?? PLEASE HELP THIS IS FRUSTRATING AND GETTING THE TIME OF YEAR WHERE I NEED IT.

There some issues with the mode door binding or the hinge are corroding causing the binding, the heater case must be taken out to access this, try getting a little rust penetrant in around the pivot first.

okay thanks ill try to put some on it. seems to work fairly easy with finger?

i've changed out the mode does same thing? mode only moves a little each way? even when off the housing?/loose...from

with no linkage hooked to it?

the mode is not turning far enough? tried oiling several areas. is working just not turning far enough to kick in defrost from floor?

Is the mode door vacuum-operated or by servo motor? If there are six or seven little colored tubes coming from the back of the mode switch, it is a vacuum operated diaphragm. If so, there may be a hole in the diaphragm (you should hear a hissing sound as you change modes). Servo-controlled doors have mode switches that are silent operating except for the slight clicking you hear and feel as you turn the dial. Being that my '95 C2500 is servo yet my '96 Jimmy was vacuum, I would err on the servo side for you..Burbans were based on the C/K trucks.

yes its got an electric motor on the heater box/floor box drivers side, motor when dialed from floor to defrost on dash,just doesn't turn far enough to engage defroster? even when i have it off the box in my hand it only moves about a 1/4inch each way? tried a new mode motor did same thing? but if i use my hand under dash i can manualy operate the blender door lever.

When moving the door lever by hand, how far do you need to move it to get full sweep? IE: are you sure the mode motor is not moving far enough?

I'm not really familiar with the GM automatic climate control systems. On Fords, there is a self diagnostic mode that may provide codes if the control unit determines something isn't working right. Part of this diagnostic mode can also be used to calibrate the servos. Maybe someone with a service manual for your Suburban will be able to provide you with such steps if they exist. It appears that one way to calibrate the mode motors is, with the key in the OFF position, to remove the HVAC control module fuse for greater than 60 seconds, then reinstall the fuse. It appears this would be the 15A radio fuse in the engine wiring harness junction block.

It appears that the mode motor contains a DC motor and a position feedback potentiometer. You could measure the voltage being provided to the mode motor as well as the the position feedback resistance as the motor runs through its range of motion. If the voltage provided to the mode motor is less than battery voltage, compare that with the voltage provided to the blend door motor or recirculate motor when it goes through its full range of motion. It looks like all three motors for the HVAC system may use the same motor system (recirc, mode, and blend/temp motors). The motor voltage would be between terminal locations 6 and 7 (wires white [mode control] and gray/black [ground]) and the position resistance would be between terminal locations 7 (ground) and 9 (poisition feedback), colors gray/black and red.

There is a TSB on the 1999-2002 Suburbans losing mode control due to lock up of the HVAC mode controller (not control head). This is TSB 04-01-39-007.

-Rod

thanks shorod i'll try this.

okay pulling fuses for 60 seconds didn't work? but seemed like a good idea?