HVAC on Auto... don't do what I did

[Thunder22]

I have the HVAC on Auto and 70*, but I must have hit the AC button at some point by accident. I discovered it when the girlfriend said "the top vents are blowing cold". I turned it off, but was thinking "hmmm, that's been on for a couple of weeks at least" and I'm used to it being on as the light is on on BMW X5's (which I've previously owned 4 of) when the HVAC is in auto (iirc).

So you're probably thinking so what.

The point is that since turning it off I'm getting better MPG. Oh, and the gf isn't complaining about cold air from the top vents.

 

[Stbentoak]

I could be wrong, but when you are in "AUTO" the AC may or may not run using its own discretion. If it was blowing cold then the cabin sensor must have thought it was above 70.
When you push the AC button you effectively "Lockout" the AC for the current cycle even though you may think your in Auto. Unless saving gas is your priority, its better to just bump up the temp if someone is cold or redirect the flow. She could also turn the temp up on her side if you think YOU still need 70....

 

[Thunder22]

yes, when in auto the system controls the ac, i'm good with how the system works, I just accidentally hit the AC button at some point. I'm not into saving gas, it was just an observation that I had the ac on 100% of the time, and after a 150 mile round trip today, the MPG improved. Since I turned it off, I've started/stopped the truck many times, and it (it being the light) hasn't come back on once.

 

[muncie21]

Air conditioning (AC) by definition can either heat or cool. The 'conditioning' part of AC, means that moisture is being removed and the temperature either increased or decreased. If it is cold and damp outside I will engage the AC while heating, so that the incoming air has less moisture.

 

[Jason in DLH]

Air conditioning (AC) by definition can either heat or cool. The 'conditioning' part of AC, means that moisture is being removed and the temperature either increased or decreased. If it is cold and damp outside I will engage the AC while heating, so that the incoming air has less moisture.

I’ve found that my AC has been on as well at times when it’s below freezing (and I don’t even use auto temp), so this is good to know. I’ve always wondered this, so thanks for clarifying.

I wonder....during the very cold winter days 0 degrees and colder we get a lot ice buildup on our wood windows during the night(which I then have to go around and wipe dry in the day when it starts melting). I wonder if turning the AC on would rectify this from happening?

 

[muncie21]

I’ve found that my AC has been on as well at times when it’s below freezing (and I don’t even use auto temp), so this is good to know. I’ve always wondered this, so thanks for clarifying.

Most newer cars have a sensor that prevents the AC compressor from engaging when the ambient temperature is at/near freezing, to prevent damage to the system. The AC light may be on (in some vehicles it blinks) but the AC compressor clutch should not be energized.

I wonder....during the very cold winter days 0 degrees and colder we get a lot ice buildup on our wood windows during the night(which I then have to go around and wipe dry in the day when it starts melting). I wonder if turning the AC on would rectify this from happening?

Your home AC is a little bit different than AC in a vehicle. Let me explain.

You are driving on a cool day (say 40*F) it's damp out and you want to both warm and dry the incoming air. The AC system will condition the air and then use your heater core to heat/blend the air so that the discharge temperature is equal to what you are requesting via the climate control in the dash.

Using the same 40* (or colder) day for your home, the big difference is that there's isn't an available heat source to warm up the air. Therefore home AC units typically only cool. Adding a 'heat pump' or inverter style AC unit (think mini-split) to your home system changes the whole game for home AC. But that's a topic of residential AC, not necessarily AC for gas/diesel powered cars.

 

[Jason in DLH]

Makes sense now, thanks for schooling me!

 

[HACK BLOCK]

I think in the car if you set it to 70* the air will come out at 70* no matter what but the fan speed will adjust to maintain the cabin temperature so in my truck I have it at 70* in the summer and 75* in the winter with the AC always on