Originally Posted by DerekHill
I have a 2001 tj and am having a similar problem. My heat and ac both work fine at any speed except only blow out the driver side vents. Should I try any of the methods above or is this a completely different issue??
Check vaccume lines and make sure the actuators under dash on drivers side is working when selecting different settings. If there is a leak the vents will default to defrost vents. If defrost is not working when selected, then more likely it is an actuator or broken arm controlling the door/flap. I had a leak where it was just enough to hold in position, but if you switched the location it would not hold or revert back to defrost. Turned out to be the boot on the vaccume line and tank under the battery on passenger side tucked into the fender. Took a bit to actually locate when the line fell off. There is a "T" where the vaccume line comes off the engine and goes into the firewall where the heater core lines go in and the other lines goes to the tank under-ish the battery. Follow the lines and look for nicks, breaks or brittle, cracked rubber boots and elbows.
As for the others. I have found the Switch goes before the resistor more times than not. I have replaced the fan speed switch 2 times in last 6 months. Both melted a bit. But the resistor is fine. No reason other than buying cheep switches that the melted.
The temp selector on dash controls the blend door. That door is located on passengers side close to center under dash. Allowing hot air from the heater core to enter the vent system or not. My 01 is controlled by an electric motor not vaccume. If the temp does not change, the motor could be bad or the switch on dash or door/flap broke. Look for cheep fix first.