Archives




View Full Version : Does the A/C go on when you choose defog, but the fan is at 0?


voodoo22
11-28-2008, 01:10 PM
I pulse the defogger off and on to avoid too much A/C use and one morning I forgot to turn the defogger back to normal air flow after turning the fan off.

I'm getting worse than normal FE on this tank because of the horrid weather, but I'm wondering if anyone with a Yaris Sedan can confirm or not that the A/C stays on when you have the knob set to defog, but the fan is at 0?

Thanks for the help.

Right Lane Cruiser
11-28-2008, 01:11 PM
I don't know about a Yaris but my Elantra doesn't engage the compressor unless the fan is on.

abcdpeterson
11-28-2008, 01:20 PM
same for my Vibe. no compressor until the fan is on.

I also believe I read in my Vibe's owners manual the compressor will not come on when it's below 40. i will verify once my wife is back with my car.

jdhog
11-28-2008, 07:29 PM
I think you're safe with the fan at 0, at least that's how I do it in my Matrix, just to allow a little air flow up onto the windshield without engaging the A/C. As soon as I put the fan to 1 I can see a little drop in impg and little increase in LOD on the SGII

FWIW I used to have a Tacoma, and there was a Mod that I found, and implemented, to allow the fan to flow up onto the winshield without the A/C coming at all. It consisted of shaving a small tab off the A/C bezel and allowed an extra position on the dial that disengaged the A/C but kept the fan and ducts running up to the windshield......

voodoo22
11-28-2008, 08:15 PM
I think you're safe with the fan at 0, at least that's how I do it in my Matrix, just to allow a little air flow up onto the windshield without engaging the A/C. As soon as I put the fan to 1 I can see a little drop in impg and little increase in LOD on the SGII

FWIW I used to have a Tacoma, and there was a Mod that I found, and implemented, to allow the fan to flow up onto the winshield without the A/C coming at all. It consisted of shaving a small tab off the A/C bezel and allowed an extra position on the dial that disengaged the A/C but kept the fan and ducts running up to the windshield......

I wish an option like that was standard. Thanks for all the info guys. I was wondering what other peoples thoughts were as I'm not a fan of having to continually more the dial from defog every time.

Kacey Green
11-29-2008, 09:10 PM
I doubt the compressor was still on, but your owners manual should tell you for sure.

JasonA
11-30-2008, 08:54 PM
With the fan at "0", the HVAC system is generally "off", isn't it? That's how it is on my Corolla. So no, the compressor would not run.

abcdpeterson
11-30-2008, 08:57 PM
Yep it's off if the fan is off.

Skwyre7
12-03-2008, 07:03 AM
The compressor is off, but some air still goes through the vents, which gets me toasty (read: I can feel my fingers, but I'm still wearing a coat) warm. I usually have it set to defrost/floor vents with the fan at zero for most of the winter.

jstol3
12-03-2008, 11:56 AM
I had a cutoff switch installed on my Mystique so I can choose whether I want the A/C comp. to be on or off. Most days I don't need it on - only when the humidity is high. The heat, def, vent, floor and panel are otherwise normal.

PaleMelanesian
12-03-2008, 02:44 PM
The compressor is off, but some air still goes through the vents, which gets me toasty (read: I can feel my fingers, but I'm still wearing a coat) warm. I usually have it set to defrost/floor vents with the fan at zero for most of the winter.

There's a measurable difference in warmup time with the temperature set to hot, but the fan off.

YarSwiss
12-03-2008, 05:55 PM
No, unless the AC button is in and the knob is set to FAN 1, the AC shouldn't be working. I set my default position to max cold, AC off and vent open when not using the AC and even then, I occasionally get the impression that the AC is on because the vent is open, but it's not.

Even after the AC has been off for a few minutes, you may still get a draft of cold/hot air comping through as the vent is pushing the remaining air-conditioned air out.

As a tip, the best defogging technique I found with the AC is to set max cold, vent open (no recycling) and fan to 2, but with no AC.

Finally, if you want to check whether the AC is on or not, you should notice a significant drop in torque when the fan is on, even slightly. Change the settings so that everything is off, and then change them to notice the difference.

voodoo22
12-03-2008, 07:05 PM
As a tip, the best defogging technique I found with the AC is to set max cold, vent open (no recycling) and fan to 2, but with no AC

Which position do you put the directional knob at?

I usually leave the fan at 0, but also have found it's best to put the fan to 2, but then have found it most effect to put the air flow direction know to defrost which automatically puts the a/c on from what I've read.

YarSwiss
12-03-2008, 10:25 PM
I put the direction knob onto up vent, which I believe is on the far right of the available options. I don't know if it actually does turn the AC on or not, but if you are driving in cold weather, the outside air being blown in on fan 2 should do the trick just fine.

voodoo22
12-04-2008, 08:05 AM
I put the direction knob onto up vent, which I believe is on the far right of the available options. I don't know if it actually does turn the AC on or not, but if you are driving in cold weather, the outside air being blown in on fan 2 should do the trick just fine.

That's what I do as well, but on that setting, when you put the fan on, the A/C goes on automatically.

Showbizk
12-05-2008, 07:52 AM
With the fan at 0 (off), I'd be surprised if any vehicle a/c compressor would be on, simply because, no matter the temperature, there is not enough air movement most of the time to prevent the condenser from freezing, unless the fan is moving more air across it. That's pretty much an HVAC fact. It's also the reason many, if not all, vehicles' compressors do not run if the ambient temperature is below a minimum, usually around 40F.
YarSwiss's advice to check it is worthwhile. While parked, raise the hood, select defog or defrost, alternate the fan between off and low for 30 seconds at a time, and you should hear the compressor coming on a few seconds after the fan is on, and remain off while the fan is off.

Right Lane Cruiser
12-05-2008, 08:07 AM
It's also the reason many, if not all, vehicles' compressors do not run if the ambient temperature is below a minimum, usually around 40F.

This is news to me. Both of my vehicles will turn on the compressor at any temp I've tried it for defrost...

RningOnFumes
12-05-2008, 08:13 AM
What? I thought this was already sorted. The AC is on if you select defrost/vent to windshield. Toyota made it automatic. AC to dehumidify the air.

Showbizk
12-11-2008, 07:55 AM
...Toyota made it automatic. AC to dehumidify the air.
As have most newer vehicles. The question that seems to have variable answers is whether the A/C will run at very low ambient temps. Mine (according to the owner's manual) in all cars I've owned with AC since the late 70's say the compressor will not run if the temp is below some minumum. And that's been around 40F.

jambo101
12-19-2008, 02:50 AM
I have no idea what Toyota was thinking when they put this mandatory air on when using the defrost mode,Yes defrosting with the air on is quicker but what about when the car has warmed up?why do i still need the air continually cycling on and off.And Toyota i know where the air button is if i need air.:confused:

jstol3
12-19-2008, 08:00 AM
I have no idea what Toyota was thinking when they put this mandatory air on when using the defrost mode,Yes defrosting with the air on is quicker but what about when the car has warmed up?why do i still need the air continually cycling on and off.And Toyota i know where the air button is if i need air.:confused:
Toyota is not the only one. My 1998 Merc Mystique is the same way. I had a cutoff switch installed so I could choose when to have the compressor on. They say they are trying to build more FE cars but then they do jackass stuff like this! I wonder how much the oil companies paid them to do that.



Copyright 2006 Clean MPG, LLC. All Rights Reserved.