It is possible to run the fan and get hot and cold air without turning on the A/C; so what does it do internally to the air? Is it needed when trying to heat the car?
A/C button turns on the A/C system which cools the air (either internal or external air). Heated air comes from the hot water that cools the gas engine. the A/C system does not in any way heat the air in the car.
Air Conditioning. in the usa, we consider it cooling. in japan, they consider it conditioning: heating, cooling, humiity, filtration. we call that HVAC, heating, ventilating, and air conditioning. how do you see it in the uk?
With a Canadian model at least, I've never seen the AC button come on by itself, if it was off, when I hit the Auto button. It will come on if I hit Front Defog button, though. That said, I know, from monitoring with ScanGuageII, the AC compressor does activate when you have Mode set to Heat/Defog. And the light on the AC button does NOT come on during this occurence. A sort-of "stealth AC" mode, lol. Maybe if Auto switches it to Heat/Defog too, though can't recall ever seeing that switch.
I believe this function is programable in the customise section of the car set up. A/C does indeed turn on in the UK if you select the windscreen (windshield) demise button.
Romario, the best way to think of the system is an integrated heating, ventilation and air conditioning system, which is marketed as "Climate Control" This is so much more than just air conditioning. Essentially you set the system on Auto and tell it what temperature you want and the system endeavours to give you that. Just because A/C is set to on, does not necessarily mean that you will be using A/C (for cooling). It is activated as required when the circumstances need its function. A/C also provides humidity control, so can also dry out damp air. This is what happens when you select the windscreen defogging function. For some reason the defogging works better when you use fresh air from outside. There is a lot of angst concerning the climate control, but my take is that people are trying to use it as a simple air conditioner not realising that air may need to be dried when heating to lower the possibility of mist forming on cold windows, caused when warm damp air hits a cold surface (your windscreen). I have always used the climate control by setting A/C on, putting it on Auto and then selecting the temperature I desire. The only adjustment I make is to change the temperature selected up or down as I see fit. It works well this way and, in the moderate climate where I live, there is almost no perceivable hit to fuel economy. In London, UK, where you live, it is even more moderate so the same will apply to you. The only concession, I make is to turn the A/C off, via the steering wheel control, when I arrive at my destination just prior to shutting down for the day, so that on the next start up the following morning I can get a shorter warm up cycle. I will then bring the Climate Control online once I am in the cruising part of my journey, but this is weather dependant—I will never compromise visibility/safety. In the depths of (the UK) winter (circa 4-8℃), I found that it was hard to keep the windscreen clear by just having the climate control on normally, and found I was using the defogging button much more extensively than I was used to. The situation is different in hotter places (where such cold temps are non-existent) such as Southern California, Arizona and Texas (e. g.) of the USA, so this advice would not be particularly applicable to those regions and similar. Hope that helps.
Maybe or maybe not, but not enough for me to worry about it. And at 4.4 - 4.7 l/100km per tank I'll take comfort and ease of use over a hard life any day.
Dolj gives a good explanation. AC means air conditioning, and that may mean cooling, or it may mean heating; it depends what temperature you choose for the cabin and what temperature it is outside. If you choose a cabin temperature setting lower than outside then AC will cool the cabin If you choose a cabin temperature setting higher than outside then AC will heat the cabin Humidity control is automatic if AC is activated. The driver has three choices in how to use the fan/cooling/heating/humidity: Click the 'AUTO' button and set the cabin temperature. Everything else is automatic Click 'AC', and then manually set the fan speed and/or recirc and desired cabin temperature. If you were in AUTO mode and then change fan speed or recirc mode then you are in mode (2) Keep AC off, and set the cabin temperature, recirc mode and fan speed yourself. In this case if the cabin temperature setting is higher than outside, the car will bring in heat from ICE use once the engine is warm. If the cabin temperature setting is lower than outside, the car will ventilate with outside air if recirc is off and the fan is running. My wife still has trouble with this setup even though we have owned Prius for over 10 years. The habit of viewing 'AC' as 'cooling' (always) is hard to break. I just tell her to use choice #1 when she is confused. And truthfully, Choice #1 works very well if you are not OCD. I live in a dry climate and often save energy by using ventilation only, but if I had to deal with humidity I would have little to no reason to stray from 'AUTO' mode.
