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Why An Air Conditioner Linked Defroster In The 9th Generation Corolla?

by Roger, April 4, 2006



Have we as drivers become so ignorant (I included) we are not capable of managing the climate control systems in our vehicles?? In my judgment the vast majority of Corolla owners buy for economical reasons. With the ever rising cost of energy (fuel) the Corolla driver is at the mercy of a 10 to 15 percent reduction in fuel economy the moment he or she engages the defroster.

Why not allow the driver to decide if he or she wants to engage the A/C when the defroster is activated. It's simple.......engage the defroster and press the A/C button if desired. But with the a/c linked defroster, there's no option and the driver takes the hit in fuel economy.

Does anyone know if Honda or Nissan vehicles have the defroster a/c linked system?

Honda has defroster linked A/C - but it can be disabled by punching and holding buttons on the climate control unit in a particular order. No idea why Toyota choose NOT to do that, unless someone can verify there is a "button" trick. I have a feeling it has something to do with Honda having a programmable ECU vs Toyota setup.

check out the manual, there might be something in there about it? or you may try calling a dealer and asking the service dept.

Add me to the list of those with the same complaint. To defrost your windshield, what you really need is just some air which is warmer than the air surrounding the windshield. The warmer air will be dryer, and should clear (defrost) the windshield most effectively. I've seen these A/C linked defrosters actually cause a windshield to fog up in warmer weather -- which is dangerous while driving in highway traffic. So this system is not only un-economical, it has the potential to cause a fatal accident.

I wish you could override this feature too, but in almost all cases the defrost works better with the AC on even though it doesn't seem like it would at first thought. This is especially true in very cold weather, running with the AC is the only way to defrost. I used to have a car that allowed the AC to be operated independently, but I almost always had to turn AC on for defrost.

one of the reasons the air cond fails is not using it regularly,

haveing the defrost - on to AC helps to reduce air cond breakdown,

unfortunately at the cost of higher fuel consumption.

Have we as drivers become so ignorant (I included) we are not capable of managing the climate control systems in our vehicles?? In my judgment the vast majority of Corolla owners buy for economical reasons. With the ever rising cost of energy (fuel) the Corolla driver is at the mercy of a 10 to 15 percent reduction in fuel economy the moment he or she engages the defroster.

Why not allow the driver to decide if he or she wants to engage the A/C when the defroster is activated. It's simple.......engage the defroster and press the A/C button if desired. But with the a/c linked defroster, there's no option and the driver takes the hit in fuel economy.

Does anyone know if Honda or Nissan vehicles have the defroster a/c linked system?

Toyota was inconsistent adopting this feature to their line of Corollas. My siblings have a 2000 LE with the link but my 2001 S air con isn't linked to the defroster. In my experience the defroster/air con link would be very useful in really cold weather with more than 2 people in the car. The Corollas seem to be poorly ventilated (inside/outside air exchange) and condensation/frost accumulates very fast on the window surfaces (particularily the passenger side front). Luckily, I have a choice.

BTW: I disagree with the 10-15% reduction in mileage when your running the A/C. In my experience its about 5% (if that) but YMMV cause I don't idle the car too much on my commute (almost no city driving).

Funny thing is that in my owner's manual it says I can override it when you clearly cannot.

In a Honda, when switched to defrost, the A/C button lights up to let you know it's engaged to help defrost quicker. Then at your option, you can leave it like that or turn it off. Pretty logical and simple and more important it gives YOU control when it's used or not.

In my Corolla, when switched to defrost, the A/C button stays dark and doesn't let you know that the A/C is engaged and give you NO option to disengage. When it's -30C and the car is barely warm, I really don't need the compressor to be engaged.

I took it to the dealer to complain and was explained that the owner's manual is wrong and that my car was operating correctly. The demo Corolla they had did the same thing. Oh well, I just end up rarely using defrost to avoid the fuel economy hit and the reduction in engine torque.

Add me to the list of those with the same complaint. To defrost your windshield, what you really need is just some air which is warmer than the air surrounding the windshield. The warmer air will be dryer, and should clear (defrost) the windshield most effectively. I've seen these A/C linked defrosters actually cause a windshield to fog up in warmer weather -- which is dangerous while driving in highway traffic. So this system is not only un-economical, it has the potential to cause a fatal accident.

 

Larry, you are absolutely correct in all aspects. The fogging is a meteorological event determined by the level of moisture (humidity) in the air.

This may sound familiar to drivers in balmy climates with high humidity ( I am in that group). The A/C linked defroster with no manual control for the A/C clears the fogging on the inside of the windshield rapidly, no question... However, the cold air directed to the interior windshield causes condensation to accumulate on the exterior of the windshield requiring windshield wiper use every few minutes to keep it clear. And, within several minutes the driver and passanger side windows exterior begins accumulating condensation, blocking the side view, as well as the ability to use the outside mirrors. And the best part, we experience this wonderful phenomenon at the cost of reduced fuel economy. How nice!! There is something wrong with that equation in my judgment.

In the engineers defense, I am certain they meant well in implementing the feature. However, it's just not applicable in the vast differences of climates. Therefore, it SHOULD have a manual override to accomodate everyone in every corner of the world.

Funny thing is that in my owner's manual it says I can override it when you clearly cannot.

I have the '04 model and my owner's manual makes no mention of any override, whatsoever.

I also took my complaint to the service department. I thought the climate/defroster control was malfunctioning due to the A/C light not illuminating when the defroster was activated. I knew the A/C compressor was engaging, as I could feel the added load on the engine and it was suddenly uncomfortably cold in the cabin. I was told by service mgr. there was NO override and the A/C indicator does NOT illuminate when the defroster is engaged.

He also said ALL Toyotas, Nissans and Hondas, as well as about 95% of the other manufacturers models in current production have the defroster linked A/C.

snip...........

He also said ALL Toyotas, Nissans and Hondas, as well as about 95% of the other manufacturers models in current production have the defroster linked A/C.

I have no doubt that is true......they do have it linked....however other car makers like Honda does allow you to override that linkage if need be. Why not let the driver have that control? I hear you just need to uplug a wire in the back of the control unit. I might give it a shot.Traction control has the same issue with some models as well.

I am glad my 95 does not have the A/C linked to the defroster.

Bikeman982

I am glad my 95 does not have the A/C linked to the defroster.

It is not linked on my 1993 or 1994's. I never have their problem.

I hear you just need to uplug a wire in the back of the control unit. I might give it a shot.Traction control has the same issue with some models as well.

 

Unplug a wire on the rear of the control panel???? I like it... Unfortunately, I am not highly wiring schematic oriented. But it shouldn't be more than a single wire of specific color, right? I'll browse around online and see if there is a wiring diagram out there somewhere. In the meantime, if you experiment with any success let us know.

I have seen the traction control option on some of the Corollas but didn't know it engaged automatically. I have only seen it with the control button or switch in the dash which I am presuming is for manual engaging of traction control.

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I hear you just need to uplug a wire in the back of the control unit. I might give it a shot.Traction control has the same issue with some models as well.

 

Unplug a wire on the rear of the control panel???? I like it... Unfortunately, I am not highly wiring schematic oriented. But it shouldn't be more than a single wire of specific color, right? I'll browse around online and see if there is a wiring diagram out there somewhere. In the meantime, if you experiment with any success let us know.

I have seen the traction control option on some of the Corollas but didn't know it engaged automatically. I have only seen it with the control button or switch in the dash which I am presuming is for manual engaging of traction control.

And you would be wrong. Traction control is automatic, but the button isn't for manual engaging. TC stands by after your car reaches 5 mph for the first time after startup and is there ready to react at any loss of traction. The button is to manually over-ride it so you can rock the car back and forth to get unstuck, etc.

Most vehicles I've had don't always run the compressor when the defrost is engaged. Most without a manual control of the compressor would only kick the compressor on if the outside temperature was above ~40 degrees F. Any colder and the system would not run the compressor.

I suspect the newer Corolla has a system like this.

If it's warm and you are running the defrost/defog, you are probably looking for the defog feature, and the compressor takes moisture out of the passenger compartment, removing the fog from your windows.

If it's cold and you run the defrost/defog, you are probably looking to clear ice from your windows and have less need of the defog feature, so the compressor does not run.

I like to have the control as well, but I haven't seen horrible fuel economy from running the A/C.

I get better mileage in spring and summer than I do winter, so running the A/C is not so bad from what I can see.



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