One thing that bugs the crap out of me is when cars automatically engage the AC compressor whenever defrost is selected.  My Ford truck engages ac for every position except one! So, I decided to rip my dash apart on the tracker to find the wire and cut it.  Well, it’s not part of the switch controls ironically but I was able to find it behind the steering wheel and unplugged it.  Fixed and now I can select AC when I want AC, which will probably last longer now as a result of being used a lot less for no reason.   

While I was at it I defeated the clutch interlock switch as well. 

I'd like to do the same.  Could you describe in detail where those wires are?  Color code?  Thanks!

Gosh I was afraid you’d ask that.  Well all I can do is describe.  But it’s obvious on my rig. 
Okay, pull the big panel under steering wheel and look back there, slight right side up high theres a bright silver box.  To the right of that there’s some plastic levers that operate the various dampers for the heater flow plenums.  Look at that and slide the heater controls you will see that lever rise up and trip a tiny limit switch.  You’ll notice that the switch is engaged only on the two defrost settings.    Simply remove that switch or just unplug it and now you have a little more control on your HVAC.  Here’s what it looks like.  I removed it but you could just unplug too.   

NOTE: I’ve read some HVAC controls on these rigs are push buttons for selecting.  My rig is old schoole slider type levers to select so this mod is only for those trucks.  If you have buttons, I’m sorry. 

There is a reason the compressor engages with defrost...part of the reason is to dehumidify the air that is blowing on the windshield.  This isn't that important for "defrosting", but if you live in a very humid area, it is essential for "defogging".  My ac leaks freon like the Valdez, so I am not able to take advantage of the dehumidifying of the air blown on the windshield, and it makes defogging the windows a pipe dream.  The other reason for the HVAC to function that way is to keep the compressor for sitting idle for months at a time.  If there happens to be any moisture in the system, it can settle in the compressor and start causing corrosion/rust.  Cycling the compressor with the Defrost function keeps the moving surfaces of the compressor lubricated and any possible moisture suspended and not settled out causing corrosion somewhere.  If humidity isn't a problem, then the defrost/defog may still work as designed, but don't be surprised the first warm day of spring when you decide to kick the air on and get the belt scream of death from your compressor.

There is a reason the compressor engages with defrost...part of the reason is to dehumidify the air that is blowing on the windshield.  This isn't that important for "defrosting", but if you live in a very humid area, it is essential for "defogging".  My ac leaks freon like the Valdez, so I am not able to take advantage of the dehumidifying of the air blown on the windshield, and it makes defogging the windows a pipe dream.  The other reason for the HVAC to function that way is to keep the compressor for sitting idle for months at a time.  If there happens to be any moisture in the system, it can settle in the compressor and start causing corrosion/rust.  Cycling the compressor with the Defrost function keeps the moving surfaces of the compressor lubricated and any possible moisture suspended and not settled out causing corrosion somewhere.  If humidity isn't a problem, then the defrost/defog may still work as designed, but don't be surprised the first warm day of spring when you decide to kick the air on and get the belt scream of death from your compressor.

right.  I understand why they do it.  I just don’t agree with it.  Because I have a button literally 1” away from this lever.  So, if I want the drying effect or not, is now up to me.  It’s a simple (very) training issue to me.  I mean what else do we need to make automatic in the car?  Why not remove all heater controls and just blow regulated air All the time?  Why can we turn our headlight switch off? (Oh wait I had to defeat that system too lol)  That way we never have to trouble ourselves with the task of reaching dangerously 18” to the HVAC system? 
And re lubrication: I’m not totally sure I buy this.  I have refrigerators, AC and other devices that sit all winter or longer, years, between running with no ill effects.  I can point to cars that sit all winter without even being driven and still works in Spring.   But, again, with this amazing button, I can use the ac compressor occasionally in winter, sometimes even for the purpose of defogging. Which I do.  Am I weird?  Why can’t this just be a line in the owners manual instead of a built in function that limits the flexibility of the system?  My main objection is the wear on parts and the drying effect on the air hurts my eyes.