Automatic A/C in a cold weather

[KVV]

CX-9 is my first car with the automatic A/C. Just curious - in a fully auto mode the A/C light is on. My car is obviously heating the air rather than cooling. Is the A/C unit also operating when it is heating? Am I supposed to turn the A/C off and keep the Fan on "auto" during the cold weather? Thanks.

[xarthan]

Sure, you are prob getting dry air from the AC to help de-fog the windows.

[ceric]

A/C serves two purposes.
Cooling and de-humidify. (Heating is another story. It needs engine to warm up first.)
Even in winter, you probably still need A/C to avoid fogging up the windows and windshield.
Keep it on, I would say. With 3.7L engine, A/C does not impose a heavy load on the engine.

[KVV]

Thank you for your replies. De-humidifying certainly makes sense.
Do I need to care about unnecessary tear and wear of the A/C compressor and other parts?


A/C serves two purposes.
Cooling and de-humidify. (Heating is another story. It needs engine to warm up first.)
Even in winter, you probably still need A/C to avoid fogging up the windows and windshield.
Keep it on, I would say. With 3.7L engine, A/C does not impose a heavy load on the engine.

[xarthan]

Thank you for your replies. De-humidifying certainly makes sense.
Do I need to care about unnecessary tear and wear of the A/C compressor and other parts?

I would think not. I had my honda accord all the way up to 115K miles and the AC was on all the time since 20 miles and never had any problems. Sure with the AC on all the time you'll be using a bit more gas.

[mihalis]

The AC will come on as soon as you turn on the rear defogger as well. Actually, my BMW had the AC come on every time the temp was below 37 degrees. I went to the dealer and had them program for that NOT to happen. Not sure if you can do the same with the Mazda, but yeah, the AC helps de-fog, so everytime you hit the "auto" button, it will come on, whether you want heat or cold air.

I do what you do, shut off the AC and leave it on manual. My wife (drives the car all the time) I believe just leaves it on auto and lets it do its thing.

[sjg]

I notice the A/C is on all the time in "Auto" as well. My last Subaru Legacy GT Limited would behave similarly but would turn off the A/C under certain cool/dry conditions. I am yet to see the CX-9 turn off the A/C on it's own. The good news is that you can turn the A/C off manually when you don't think you need it and all other "Auto" features (temp, fan speed, fan direction) seem to remain under automatic control. If you notice any fogging or are uncomfortable with the humidity in the car, just press A/C again and it will re-engage. A/C can be manually turned on and off repeatedly without disturbing the other automatic settings.

[Touring9]

The light on does not mean the compressor is on, but simply available when called for.

If you watch the system in full auto on a cold day, it will switch to low speed defog while the engine is cold, and end up on floor heat when warm air is available. In full auto, if your windows start fogging up you just press defog and it will turn on the compressor and adjust the vents and temp. Press it again, or Auto, and you're back to normal. Very nice vs. having to manually adjust everything to defog.

It really is a full auto system, and we leave it there 90% of the time.