Is there any setting on our HVAC controls that will force the A/C without us knowing it? The reason that I ask, is because when I have the blower on face/floor mix with the dial all the way to the blue zone, the air coming out of the vents feels colder than the outside air. Just a slight bit colder though. If I hit the A/C button, the light turns on and the air gets a lot colder.

From what I know about A/C, it's either on or off, nothing in between. Shall I assume this anomaly is purely the product of defective neurons between the hand and brain, or is it possible that there are other forces at work?

 

well there is always air coming through your side vents no matter, what, and yes, the temp depends on where your *** is set

 

put it on "recirculate" and then the vents will be closed. other than that, you're stuck with whatever temp your **** is set at. sometimes, i don't even need to turn on the heat on cold days. i just drive and the air from the outside will be forced into the inside and it gets really warm.

 

I must not be explaining myself well. I'm noticing that the air coming out of the vent is colder than the ambient air outside, without the A/C on. I'm trying to figure out if the A/C compressor and other bits are running when I don't choose it to be on.

 

Like Big_Bird said, your vents are always open unless you put it on recirculate. If you are doing 65mph the air coming in is going to be chilled a little because of the speed that its entering the car. On the flip side, if your control is set to warm, the air is re-directed around the heater core then into the cabin. Hope this helps.

 

if you had the a/c on for a while and turned it off, the air comes out from the vent will be colder than the outside air

 

The real temperature of the air shouldn't go down as speed increases. If anything, friction should make the temp go up. At speed, the perceived temperature should be lower with a hand out the window than from the vent, as long as the car is going faster than the air coming out of the vent. Evaporative cooling and such.

The only solution I can come up with that would make any sort of sense is that path the air travels though on its way to the vent is surrounded by materials that are temporarily cooler than the outside air, say from sitting overnight.

I think we can drop this. Thanks for the input.

 

Well there is certainly not enough friction to make the tempature of the air dramatically increase to a level where you can realize that it is much hotter.

Consider the 2 scenarios.

A. 85 degrees, sunny, 5 mph wind
B. 85 degrees, sunny, 20mph wind

Which breeze is going to feel cooler? Obviously the 20mph breeze
The wind may not necessarily be colder, but it sure does feel colder
And thats why the air flowing through your AC wents feels colder.
Also remember, the air thats in your consider is stagnant, and will increase in tempature from the sun, car, and your body.

Well, maybe this helps.

 

You should be able to feel a performance difference if your a/c is on. One thing i noticed too is that the a/c pump turns on when the defroster is on (defroster/foot vents) , even thought the light for a/c is still off.

 

I think we're saying the same thing about evaporative cooling. Maybe one day I'll use a thermometer to measure this.[/quote]

 

When the setting is set to the floor/defrost setting, even without the A/C light on, the A/C is actually working. I noticed this as well when I first got my car and asked a tech at the dealership.

 

Reeeeeeally...that would make me feel less crazy

 

Yeah it definately does come on. Next time you're driving, drive at a steady speed with the foot/defroster off and then turn it on, you should feel a very distinct lag and hear the pump kick on

 

I noticed the same thing you did MonkeySauce... recently as well, as the weather in Philly has been up and down. I've experienced days where I've needed the A/C (because I just had my windows tinted).. on days that I didn't need the A/C just cruising with the windows up (allowing tint to cure), I noticed the air coming through the vents were as cool as if I had the A/C on low.

I don't encounter the same lag as I do when the A/C is actually on, and I think what BEazy said above is the most probable scenario. Air being directed around the heater core when the **** is turned towards the warm zone. And coming straight through when it's turned to the cool zone, giving you the impression that you're getting conditioned air.

 

Deceiving, isn't is? I wish the light would just turn on anytime it was working.

 

not to take your thread OT... but another "weird" thing I notice is that if you just have the vents open (AC not running), and open the sunroof, an insane amount of air comes through the vents while you're at speed.

I'm sure it has to do with pressure differences, but its pretty cool