Why did Toyota do this ???

[nuclear3579]

My g/f has a '98 Tacoma 4wd, and every time you move the selector knob to defrost, it automatically turns on the AC, bypassing the AC button itself. How stupid! We usually run the defrost when it's raining or snowing out, and we don't need the AC on as well. Why would Toyota do this, I honostly don't see any reason for it. I never use the AC in the winter time, yet we use the defrost all the time to help clear the windshield. Toyota wanted the AC on all year round for the defrost?
I'll look this weekend, but I assume there's just a wire that I can snip behind the console to prevent the computer from knowing when I put it in defrost. Anyone do this simple mod before? And why did they configure it this way?

[cep89]

A lot of car makers run the A/C to dry the air in defrost. It also helps to keep the A/C lubricated.

[outdoorsbc]

It removes the moisture from the air quicker, thus helping with defrosting and fogging windows.

All the newer cars I know of use the same technique, although sometimes I wish i could bypass it to save on fuel. But overall, it doesn't make that much difference.

[Mike Kelly]

A/C not only cools the air, but it removes the humidity. Since the the point of "defogging" your window is to remove the moisture build up on your window, when you move the vent to the windshield, the A/C kicks in and helps to remove the moisture from your window.
My '88 did not have this feature, but I tested it both ways, and with the A/C on it worked much better.