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2009 - How do I disable auto A/C when selecting defrost?

('09-'13) 
33K views 69 replies 38 participants last post by  ruderegime 
#1 ·
I have always detested the idea of automatically turning on the A/C when selecting the defrost airflow position. Yesterday I drove home in mid 60's temps with light rain. All I needed was a little warm air on the windshield, but the engineers at Subaru decided that I should have the A/C running the whole time.

I'm guessing that there are 2 wires on the back of the air flow dial, and by disconnecting them I would have the option of turning the A/C on when needed with the standard switch.

Any hints or tips on how to do this on my 2009 2.5X ??

Besides this little annoyance I love my 2009 Forester :woohoo:

Thanks !!


Mods, not sure if this should be in "How to" or "Interior..." please move as you see fit.
 
#2 ·
Not sure how to disable, but virtually every car on the market runs the A/C compressor on defrost/defog because the A/C will dehumidify the air and help defog the windows in a major way. I am not aware of any car that does not run the A/C in defrost/defog, actually--oh yeah, my '91 BMW 318is does have 3 sliders for dash, vent, and floor air, so the A/C is totally independent on that car.

My last car was a Protege5 which had the logic error (I assume) of running the A/C compressor when the floor vents only were on--the only position on the dial where the A/C did not run was the combined floor and dash vent position(!?) So I usually kept it on that position, and considered that an annoyance. Some engineer was asleep when the switch was designed on that car, I think.

George
 
#4 ·
You can unplug the connector at the compressor, or wire in a switch to disable it, but all cars that I know of kick on the Compressor when in Defrost mode.
 
#6 ·
A/C equipped cars have done this since the 60's for the reasons above. What probably bugs you or brought this to your attention is newer Subarus have an indicator on them letting you know A/C mode is now on.

Our daughters 95 Escort does it. I can hear the compressor cycle, but the blue A/C light does not illuminate when Defrost is selected.

My wife's 04 Highlander also cycles the compressor in defrost, but her A/C indicator doesn't illuminate either.
 
#8 ·
Thanks for all the input, but to those of you who maintain that every car "does that"... My new Forester replaces a 2004 VW Jetta. The Jetta did not automatically turn on the A/C when air was directed to the Windshield. Before that I had a SAAB 93, it also did not automatically turn on the A/C when defrost was selected.

I'm planning on installing a subwoofer before too long which will require that I tear into the dash. I'll look around while I'm in there to see if I can find a way to easily disable this "feature". If anyone has any tips I'm all ears :) :)
 
#9 ·
Yeah, it's "normal" operating procedure. For example, from page 4-4 of the '09 Forester manual:

NOTE
When the dial is placed in the “(windshield defrost icon) ” or “(windshield defrost + footwell icon) ” position, the air conditioner compressor operates automatically regardless of the position of the air conditioner button to defog the windshield quickly. However the indicator on the air conditioner button will not illuminate.

At the same time, the air inlet selection is automatically set to “outside air” mode. In this state, you cannot select “recirculation” mode by manually pressing the air inlet selection button.

Also, you cannot stop the air conditioner compressor by pressing the air conditioner button.
I understand why car manufacturers design the system this way, if for no other reason that to run the A/C system occasionally during the winter to help lube the seals.

But, I'd like to see a wider range of operational modes. For example, the A/C system in my old MY00 Ford F250 SD pickup works similarly if the outside temperature is above ~50 F (~10 C). Otherwise, its A/C compressor stays off.

HTH,
Jim / crewzer
 
#10 ·
Agreed, I think the other reason that manufacturers design systems like this is because our society has become so uninformed that many people don't even understand that the most effective windshield defrosting occurs with A/C on and recirculate off. Add to that the fact that someone who gets in a wreck because they couldn't see could sue the manufacturer, and the easiest choice is to dumb the system down to the lowest common denominator.
 
#12 ·
I have always detested the idea of automatically turning on the A/C when selecting the defrost airflow position. Yesterday I drove home in mid 60's temps with light rain. All I needed was a little warm air on the windshield, but the engineers at Subaru decided that I should have the A/C running the whole time.

I'm guessing that there are 2 wires on the back of the air flow dial, and by disconnecting them I would have the option of turning the A/C on when needed with the standard switch.

Any hints or tips on how to do this on my 2009 2.5X ??

Besides this little annoyance I love my 2009 Forester :woohoo:

Thanks !!

Mods, not sure if this should be in "How to" or "Interior..." please move as you see fit.
My 03 Jeep Liberty had this feature as well, but only if the temperature was below 30-35 degrees. Later Jeeps had an On/Off switch for the compressor. Some owners installed their own switch.
 
#14 ·
A simple MOD to disable the A/C when defrost is selected.

This feature is very easy to disable on the '03-'08 X models! All you need to do is pop off the linkage that turns on the A/C when defog/defrost is selected. After the linkage is removed, if you want to use A/C with the defog/defrost, you simply press the A/C button. This MOD is just as easy to undo, just pop back in the linkage.

As to the automatic climate control, it simply a matter of pressing the A/C button to turn off the A/C, so no MOD is needed.:

Bobby...
Here's a picture of the linkage:
523046


Forum member @Snow drifter did this simple MOD on his Forester & has detailed pictures on his post, which you can view here:
['07 FSXT Member Journal] ['03 X Member Journal]
 
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#22 · (Edited)
This feature is very easy to disable on the '03-'08X models! All you need to do is pop off the linkage that turns on the A/C when defog/defrost is selected. After the linkage is removed, if you want to use A/C with the defog/defrost, you simply press the A/C button. This MOD is just as easy to undo, just pop back in the linkage. :wink:

As to the automatic climate control, it simply a matter of pressing the A/C button to turn off the A/C, so no MOD is needed. :smile:

Bobby...
+1

I was going to install a cutoff switch but this is better. :woohoo:

But where do I find this linkage and how do I perform this simple surgery?

--------------------

Also if I were to install an isolator (econo button) switch for the AC, how does this effect the general operation of the heating/cooling system?

Does the climate control go nuts or is it unaffected!
 
#18 ·
I have a MOD in our '95 Neon Sport (bought it new) to disable the running of the A/C defog/defrost, unless it's switched on. The A/C has never been recharged & it cools way better than A/C in in the '03 or '07 Forester! Bottom line, not running the A/C during with the defog/defrost won't cause any problems.

Bobby...

['07 FSXT Member Journal] ['03 X Member Journal]
 
#20 ·
There is an easy way to disable this that does not involve any modifications.


1) turn the dial to defog, A/C will go on
2) select the A/C button so the light comes on
3) de-select A/C so the light goes off
4) defog is now running WITHOUT A/C
 
#23 ·
There is an easy way to disable this that does not involve any modifications.


1) turn the dial to defog, A/C will go on
2) select the A/C button so the light comes on
3) de-select A/C so the light goes off
4) defog is now running WITHOUT A/C
Hmmm... I have to admit I've never tried this. I'm curious if the A/C does stay off, or does it goes thru a timing period & restart? Since in the defog/defrost mode, the A/C light doesn't come on (manual controls, not automatic). It would be difficult to tell it was running, unless you felt the cold, or the added load on your engine?

Bobby...

['07 FSXT Member Journal] ['03 X Member Journal]
 
#25 ·
My '90 Miata does not do this. A/C is always selectable no matter what the other settings are at (other than fan-off). Not that I never use the A/C with the defroster, but I find it an added convenience to be able to choose to do so when I want to.
 
#34 ·
deactivation

With our 1998 honda accord, shutting off the main airconditioning select button would deactivate the air in defrost mode. In my 1995 neon I notice a great loss of performace in defrost mode (air conditioning was always on) and a significant loss in mpg. I found a fix on the internet to drill out the circuit behind the defrost selection knob. If I do need some air conditioning to defog my windows in defrost mode I turn the fan selection knob to the blue area (air conditoning). My temp selection is still in the red area for heat. It works great! My acceleration on cold morning start ups is dramatic and my mpg is up! From Ohio. I also routinely disable airconditioning on acceleration with this 5 speed manual. It blows cold air for a good 20 seconds before it needs to be switched back. I average 36 to 40 mpg this way. With the air on all the time in the summer I average low 30s. There are patents from the 60s and 70s detailing how to do this during acceleration. But I don't think any of the auto makers use this.
 
#35 ·
I think the prior post is correct. The vast majority of cars are turning the AC on whether you know it or not. Just adjust the temp to something comfortable & let the compressor do what you are asking it to. My headache with my 2005 is that when I select floor/defrost I can get moderate auto-fan speed (and the noise that goes with it) but if I select full defrost it goes into super-turbo-full-panic-defrost-now-or-we-all-die fan speed & I have to turn up the radio to hear over it.
 
#38 ·
I tried that on my '95 Neon & there was a problem. The A/C is wired thru the ECM & when it senses the A/C was selected, it increases the engine idle to compensate for the additional load (if it was there or not). That meant the engine would idle at 1500 RPM+ without the load of the A/C compressor. I ended up placing a switch on the A/C on sense lead & that worked perfectly.

I'm not sure the Forester would act the same, but I suspect it would.

Bobby...

['07 FSXT Member Journal] ['03 X Member Journal]
 
#39 ·
Hi,

I have a 1999 Outback and need help with this too! My compressor siezed over the summer, and I had planned to put off the $1000+ repair until next spring, that is until I discovered that the defroster engages the a/c compressor. I live near Lake Tahoe and cannot live without my defroster! Any suggestions on how to disable the a/c compressor so that I can make it through the Winter? I know this might not be approved, but can I just cut the a/c belt?

Thanks!
Jenny
 
#40 ·
I see this is your first post, so welcome to the forum from Oregon!

For your situation, I'd suggest just unplugging the wire that operates the compressor's magnetic clutch. You should see it near the top of the compressor. There may be an issue with the engine idling faster when the A/C is being used... so the ECM thinks, but give it a try to see what happens. I'd do this before cutting or removing the belt.

Bobby...

['07 FSXT Member Journal] ['03 X Member Journal]
 
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