Does 'defrost' setting, use air conditioner?

[mr_Cash]

... even if the air conditioner button (and its light) is off?

Full question and related sub questions, at:

**********.com/forums/

Anyone know?

[jwight]

According to the 451 owners manual it does*:

Warning!

When the recirculation mode is switched on, windows can fog on the inside immediately. Fogged windows impair visibility,endangering you and others. If the windows begin to fog on the inside, switching off the air recirculation mode immediately should clear interior window fogging. If interior window fogging persists, make sure the air conditioning is switched on, turn the air distribution control to position [defrost] (page 150) and increase
air volume 1.

*Actually, the answer to your question is no, not if the A/C is off. The manual says you have to have the A/C on to get the full defrost effect.

[pickledchang]

if it does, you should be able to feel the compressor kick on and off as you are driving. on most cars you can anyway...

it would probably be most noticeable at a slower speed for the highest gear, say 45mph or so.

[mr_Cash]

Originally Posted by jwight

According to the 451 owners manual it does*:



*Actually, the answer to your question is no, not if the A/C is off. The manual says you have to have the A/C on to get the full defrost effect.

Well, the page before, is the confusing one.

which says (page 152 of the smart manual):

! Do not turn the air distribution control permanently to position "defrost". The air conditioner switches on independently of other settings. The indicator lamp on switch '2' then does not come on.
The vehicles fuel consumption increases and the driving performance may be influenced.

********

This is confusing, and I think it may mean, that when its straight up in the 'Defrost' position, even if the air conditioning light is OFF, the air conditioner will run in tandem with the DEFROST when its in the straight up setting position.

Notice the warning, about worse fuel consumption, and that the air conditioning light NOT coming on, and the air conditioning 'switching on' independently of other settings.

The other notice (not sure which page) is the air conditioner does not work when the temp is below 36 or 34 degrees F. So, withthe defrost striaght up, on Defrost, with the temp only 15 degrees, maybe the air doesn't come one. But if 40 degrees F, and the defrost is in the straight up position, it sounds like it WILL come on, even though its light, at that time, will not come on.

The buick lesabre works like that. shift to defrost, and one can hear the air conditioner come on, even though the Air conditioner controls, are not engaged.

This would explain, why they say, in the defrost mode, it can increase fule consumption.

So, it seems this question remains:

1) Does it work like the Buick Lesabre, where, if on Defrost, even if the air conditioner isn't turned on, the air does come on when defrost is selected?

2) If "number one question above" is true, ... is it also true on the smart, when the setting is half defrost, and half chest air (pointing north northeast)? or, on the other side, half defrost, and half feet air (north northwest)?

Until this is resolved, to be on the safe side, and to not waste fuel, nor reduce performance, I plan to keep the indicator, NOT pointing UP on defrost, but instead I will point it straight DOWN, half way between the chest air and foot air controls. ... the number 2 question above, if known, would be very helpful, since i would like to put it hlaf way between the chest air and defrost, when the fogging of the window occurs to a small, slight degree.

Again, if anyone can confirm the precise answer, maybe with verification, please post. (I suppose I could ask the service department on a visit next week, if I can remember to ask it.)

Or, as pickledchang suggests, listen closely to the engine, in 4th or 5th gear, when the temp is above 40 F, to hear if the air conditioning compressor cycles on, when the control is placed in defrost, without turning on the air conditioner and its light.

[oldbike]

On most cars, the A/C compressor is cycled when in the defrost position in order to keep the refrigerant oil circulated through the system. To “exercise� the compressor, so to speak. The cycle time is short, so the affect on fuel consumption is minimal.

[mr_Cash]

Asked service dept 3/4/08.

Their reply, in post #3, in the thread at:

**********.com/forums/

[saronian]

We ran through this issue on the Scion xA a few years ago. Many were disappointed with the mileage and it was noticed that turning vent knob to defrost would activate the A/C, bypassing the A/C switch.

Of course, as mentioned above, you can hear/feel the compressor activating.

[bobnyuma]

Also, as an HVAC type person the defrost mode needs warm "dry" air to defog/defrost properly. The A/C unit is actually de-humidifying the air, just like your house a/c unit does.. Makes the defog-defrost system work more efficiently.

[SmartAzz]

Originally Posted by bobnyuma

The A/C unit is actually de-humidifying the air, just like your house a/c unit does.. Makes the defog-defrost system work more efficiently.

This was one of those great realizations way back when I first started driving, I was so frustrated dealing with fogged windows and discovering that using the AC made all the difference was a revelation

[SmartCard]

Originally Posted by bobnyuma

Also, as an HVAC type person the defrost mode needs warm "dry" air to defog/defrost properly. The A/C unit is actually de-humidifying the air, just like your house a/c unit does.. Makes the defog-defrost system work more efficiently.

....and also throwing warm defrost air onto a cold windshield only makes matters worst! I found this out once surprinsing in my MINI, which does not automatically turn on the A/C in defrost mode. In some systems (Chrysler for one) not only does defrost activate the A/C, but also switches the vent position from the closed, recirculate position, to open vent (outside air)...all in an effort to get rid of the moisture. Most cars I have been in DO turn on the A/C led to let you know its on.