To prevent the air conditioner from automatically running while defrosting, there are a pair of microswitch connections that are located under the mode selector (rightmost knob), that can be removed.

1. Remove the three knobs from the HVAC controls.
2. Remove the three screws located behind the knob locations.
3. Remove the two screws located in the center vents with the vents pointed fully up.
4. Remove center instrument cluster. (Note: The main retaining clip is located at the center of the top portion of the cluster. Support the cluster to prevent damage to the wiring harness.)
5. Locate and slip off the two white connectors which are found under the mode selector switch on a pair of black wires which run from the blower switch to the mode switch.
6. Tape and stow the connectors to prevent rattles and/or shorting.
7. Test for desired operation.
8. Restore cluster, screws and knobs.

http://www.tundrasolutions.com/forums/garage/faqs/lighting/images/microswitch.jpg

I've been using this mod for years and it's great! No need for AC when defrosting in the winter, might as well save the gas.

I am a little confused on this? The air conditioner comes on to pull moisture from the air in the cabin to prevent the fogging of the windows. If you remote start the vehicle and it is warm by the time you get in, yes the need of running the AC is gone, being that the cabin is at a temperature where the windows would not fog up once you got in. So why disconnect besides saving a bit of gas from the AC pump kicking in, but then if you are remote starting the truck you are wasting more gas than if you got in and just waited for it to start to warm up and drive off.

Not looking for a debate on this. Just something I learned while working on my own vehicles over the years.

I don't know about other people, but for me in the winter the air is very dry, so if you're using outside air and heating it there is no need to run the a/c pump to defrost. When it's very cold out you often have to run the defroster constantly to keep the windshield clear, so the gas savings from this free mod are not insignificant.