I have seen various threads about problems with heater/ac system. Most tend to direct you to the blend door or vacuum issues. I have a different issue. You are either hot or cold during the winter. My blend door works and is not bound up. The motor works, however it doesn't start to move until the temperature control is half way then the blend door motor travels fully. So it is either full one way or the other. Does this sound like the control unit itself?

 

I would still drop the little motor feller, and check the coupler. Sounds like yours is broke.

 

Did that. All looks good. Motor just doesn't find any other position other than full one way or the other

 

Oh, I already installed a new coupler. Can I take my little motor and and connect it to a friends 2001 2500? Don't want to mess up his control unit

 

Set both controls to the center temp setting before removing either one. And put it back to center before taking it out.

Wonder if 'resetting' the motor would help.... there is a procedure for that on HeaterTreater.Net.

 

Did that too. Put the 9v to it and it rotated smooth with no issues. It is acting like it doesn't get any change in voltage till control is mid way then it goes full one way or the other

 

Ok, looks like three wires going to the little motor feller.... Dark Blue should have 12 volts with ignition on, Black w/lite green trace goes to ground, and then, the wire we are interested in.... Yellow with orange trace goes to the control ****, which is a variable resistor.

Unplug the little motor feller, put your probes in the the B/LG wire (red probe), and the Yellow/Orange wire (black probe), turn ignition on, run the temp control **** thru its full range of travel, see what voltage does. if you have to turn the **** quite a bit before voltage starts changing, control is bad.

 

Similar problem with my 99 ram. Cabin temp control, especially with AC, has little modulation. Freeze you or nothing. Sage advice on this one? Check the door motor? Replacing the temp controller looks un-fun.

 

Check out heatertreater-dot-net. The coupler is not too bad to access.