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I had read through 1999 Ford Escort Owner’s Manual, and have few questions regarding air conditioning modes. The manual’s section on climate control states:

The air conditioning compressor will operate in all modes except [floor] and [panel]. However, the air conditioning will only function if the outside temperature is about 10°C (50°F) or higher.

  1. Is it normal that A/C is engaged in most climate control modes outside of clearly marked [A/C], and [Max A/C]? Is it model-specific feature, Ford deal, or many manufacturers A/C units work the same way?

  2. From maintenance standpoint (wear and tear of the A/C system, extra load on the engine etc.) does simply engaging the compressor and “functioning A/C” differ much, if at all?

  3. Similarly, how big is the difference between [A/C] and [Max A/C] modes? Somewhat counter-intuitively, [Max A/C] is more economical (it is obvious once you know that it is the only mode that recirculates interior cool air, it is just not obvious to know that), but how much more?

  4. I understand the idea behind using A/C in [Defrost] mode (A/C removes considerably moisture from the air, thus it is used to prevent fogging of a windscreen), but why is A/C used in combined [Floor and Panel] mode? Especially, since individually [Floor] and [Panel] are A/C-free, as mentioned above?

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I've never understood Ford, or many other domestic (at least, to me here in the US) car makers' reasoning behind their climate control systems. Later models are starting to have more digital and better controls, but the model year you have is a prime example.

For domestics, Max A/C is recirculate and the A/C 'switch' is usually combined in the vent selector, as below:

enter image description here

So if you want conditioned air on your feet, no dice. I don't know why anyone would want that, but it's nice to leave the option available instead of nearly arbitrary restrictions in place by design.

In comparison, the Japanese vehicles that I deal with daily have a control system that makes sense to me. There's a:

  • Fan speed knob
  • Temperature knob
  • Vent selector knob
  • A/C button
  • Recirculate button

See below:

enter image description here

So you can have any combination you want. As far as I know the only exception is the A/C system pressure/temperature switch that cycles the compressor clutch on and off when in use. But it still allows you to use the A/C in whatever vent and temperature combination you want. This allows the compressor to run in the winter (like, below 50 degrees F). This is good because it allows the refrigerant oil to circulate and keep the seals in good working order.

So, with my rant now over, to answer your questions:

  1. It's a Big Three thing. I couldn't tell you why they make them like this.

  2. I'm not sure what you are asking. But if the compressor is engaged, the A/C system starts working. They are the same thing. Your vents may or may not be routed around the evaporator in the dash, but the system is still working nearly as hard.

  3. This is my biggest gripe. For example: If I see a dead skunk ahead and I want to minimize the amount of smell entering the cabin, on a domestic that means I have to select "Max A/C", of course. It's really not obvious and the majority of people I ask have no idea if they are not even slightly interested in cars. However, it's mostly in the past now; I know Ford has jumped to a Japanese like system on at least some models.

  4. Well, there is no good reason. So it's not that big of a deal. But, like I said above in my huge rant, what if someone doesn't like the dash vents blowing dry air at me? What if someone wanted to have cool, dry air on their feet during a hot summer? They can't.

For me, the Big Three systems don't make a lot of sense. I'm biased though because I've grown up around Japanese cars. That and I'm a programmer and I like lots of features and switches (which end users don't like!)

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Is the "big three" system still popular? I haven't seen that in any Ford or Chrysler newer than 1995. -- They either have the "japanese" style switches, or a completely digital climate control system that escapes me. –  Robbie Feb 8 '13 at 22:09
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Not as much, in my experience. My 2012 Focus has separate fan, vent, temperature, A/C, and recirculate controls but if you turn the temperature knob all the way cold, it enables recirculate automatically. Likewise, if you turn the vent knob to full defrost it turns on the A/C. Much better, still kind of irks me but i can understand it. –  Nick Feb 9 '13 at 3:30
    
@Robbie, as you can see in this question, 1999 Ford (third gen. of Escort from 1997 to 2002) does, so does my father’s 2005-ish Taurus and 2003 Expedition. –  theUg Feb 9 '13 at 6:53
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