DIY: Unlink A/C from Defroster

[stran]

My first DIY post.

Total Time:
7 mins (if you know what you're doing)
20 mins (if first time opening the dash)
2 hours (if you're have two left hands or missing your opposable thumbs)

Tools:
Small flathead screwdriver to disconnect wire harness and push in the little clips that holds the plastic pieces together. (But not required. I could have done it with my keys or just my fingers.)

Follow instructions for changing the LED to access the back of the vent dial. Everything comes apart really easy. http://www.yarisworld.com/forums/showthread.php?t=9857&highlight=led+dash On the back of the circuit board (the one with the A/C button), there is a momentary switch (momentary means it requires continuous pressure to be closed) with a little metal arm. I know this description is vague, and I'm sorry I don't have pictures, but there's nothing else on the back and once you're there, it'll be obvious. Bend the metal arm a few times and it breaks right off. Presto! No more annoying A/C with defrost. Reassemble.

How it works: the back plastic piece has a ridge that engages when the vent knob is in the defroster mode. The ridge presses on the metal arm to trigger the momentary switch. No metal arm means the ridge can't trigger the A/C switch.

For the belt and suspender people to check you have the right switch (which is what I did), you can turn on the car and press the switch and see if the A/C turns on. It's easiest to tell when the car is fully warmed up since the difference in idle speed between A/C off and A/C on is very noticeable. I also had a scangauge to check fuel flow, but you can open the hood and check the condenser fan.

Tips:

Leave the vent dial knob all the way to one side (like face vent) so when you reassemble, you don't have to worry about aligning the indicator.
There's a little bit of grease on the knob to lubricate the gears. Having some paper towels is handy.


Man, this mod made my week. I've been pissed at my defroster for so long. Maybe someone can post pics. I don't have a digi-cam.

Though, the knob has a few sticky points. I didn't pay enough attention before to know if I made it stickier or it has always been this way. I can't think of anything I did that would affect the smoothness of the knob.

[IllusionX]

things i've already known...

but keep in mind that you are also disconnecting the ceramic heater built into the system. I know you live in Cali and don't need any heat.. but other might want to know.

[stran]

things i've already known...

but keep in mind that you are also disconnecting the ceramic heater built into the system. I know you live in Cali and don't need any heat.. but other might want to know.

what ceramic heater?! yikes.

the heat still works. the hot air comes from the heater core which is a mini-radiator powered by engine coolant. what's the ceramic unit for?

[Rick]

It's been a while since I studied that in the factory manuals, but I recall that the PTC heater is a supplimental electric heat source that is enabled by turning the temp dial to MAX. It does not require selecting one of the Defrost related air positions.

There is actually a separate controller that monitors airbox temp and climate control settings to decide if and when IT will activate AC compressor and/or PTC heater.

The PTC heating element, when enabled, allows for faster cabin warm up and assists when the traditional heater core can't keep up with extreme low ambient temperatures.

I'll know for sure soon. I'm definitely going to disable the forced AC when defrosting and here in MN it will be very obvious if the PTC heater function is then missing.

[stran]

I love having a searchable factory repair manual.

The PTC heater operating conditions are as follows: "engine at idling speed or faster, ambient temperature is 10C (50F) or less, engine coolant temperature is 65C (149F) or less, and No. 3 heater control knob setting is MAX HOT." Also, blower has to be on.
[page 54 of A/C manual]

So PTC is not affected by defroster operation.

I think this is only for people with winter package, though I will check my car when I get a chance.

[IllusionX]

I have posted the PTC heater diagram in the other thread. I was told by a very experienced toyota mechanics that it had to be in either defrost mode AND max hot and max air.

i will check it out tomorrow when i warm up the car.

[DanQ]

Can you manually turn on the A/C with the button when in defrost mode "after" the mod?

[stran]

Can you manually turn on the A/C with the button when in defrost mode "after" the mod?

yup.

[IllusionX]

push the AC button :rofl:

[CTScott]

I have posted the PTC heater diagram in the other thread. I was told by a very experienced toyota mechanics that it had to be in either defrost mode AND max hot and max air.

i will check it out tomorrow when i warm up the car.

I just checked the manual and verified on the car that the PTC Heater will run with the blower direction control knob in any position and with any fan level (except off).

[YarisSedan]

Your supose to have ac on with the defroster. Thats how it defrost. By supplimenting the heater by removing the moisture. Otherwise your window will fog up.

[IllusionX]

I just checked the manual and verified on the car that the PTC Heater will run with the blower direction control knob in any position and with any fan level (except off).

great to know... sorry i didn't report back. there is actually a switch when you turn the heat all the way to "max hot".. so i guess it is the PTC heater...


Your supose to have ac on with the defroster. Thats how it defrost. By supplimenting the heater by removing the moisture. Otherwise your window will fog up.

Sometimes... it is enough with just hot fresh outside air to defog. I guess i will go ahead and unhook that wire one of those days.

[DanQ]

yup.

thanks, I didn't see any reason why it wouldn't but just wanted to ask since this is a one-way mod.

[Rick]

It doesn't have to be a one-way modification. I unsoldered and removed the microswitch instead of breaking off it's actuator. I can reinstall it if I ever want to. BTW, it's working great so far.

The older people living in very cold climates already know this, but defogging and defrosting are sometimes very different animals. Sometimes you just need all the raw heat you can get into the windshield glass. The 20 deg F or so that the AC knocks off of the defroster outlet temperature is sorely missed. Dehumidifying air that is already close to 0% RH is a lost cause anyway.

Sometimes just some air movement onto the windshield glass is enough to keep my 'personal' humidity from condensing there. It really bugs me to take the AC mileage hit just to have a small airflow onto the windshield.

Toyota ( and others) took the safe way out from a liability perspective and made the AC operation automatic so people don't need to understand dewpoints to properly use defrost/defog. It limits the defrost capabilities but does keep the lawsuits down.

[SilverGlow]

Why would anyone disconnect A/C to the defroster mechanism?

There is no faster way to remove moisture from the windows and air then using an A/C. If you don't like the coolness, move the temp control to full heat.

This DIY has to be the most idiotic yet! And for what benefit? Surely not for gas savings, as the savings is insignificant....you really need to fill your time doing something useful, productive, and not devoind of logic, and utility.

[stran]

Why would anyone disconnect A/C to the defroster mechanism?

There is no faster way to remove moisture from the windows and air then using an A/C. If you don't like the coolness, move the temp control to full heat.

This DIY has to be the most idiotic yet! And for what benefit? Surely not for gas savings, as the savings is insignificant....you really need to fill your time doing something useful, productive, and not devoind of logic, and utility.

I have a ScanGauge so I know exactly how much gas I use. When I idle, I use around 0.16-0.21 gallon / hour. With the A/C on, I use around 0.38 gallon / hour (I think it's 0.38. I haven't used the A/C in so long I don't remember).

So I reduce my gas consumption by half or more by cutting out the A/C.

Also, when you have a cold engine, you have no heat. So it's nice to be able to run the defrost without making the inside any colder.

[WolfWings]

Why would anyone disconnect A/C to the defroster mechanism?

There is no faster way to remove moisture from the windows and air then using an A/C. If you don't like the coolness, move the temp control to full heat.

This DIY has to be the most idiotic yet! And for what benefit? Surely not for gas savings, as the savings is insignificant....you really need to fill your time doing something useful, productive, and not devoind of logic, and utility.

So how does having bone-dry air on the inside of the car, help remove frost and ice on the outside of the windshield? Glass is a moisture barrier.

This mod is for those that benefit from the added raw heat, including the ceramic heating element, to defrost their windshield. You're confusing defogging the inside (windshield air flow w/ AC on) with defrosting the outside (windshield air flow with maximum heat) in this case.

Also, I can give a real-world example: Security guard watching a landslide area in your own personal vehicle on a cold night. I've done that before, had to huddle inside my vehicle to stay warm some nights, '87 Corolla FX I had until I bought my Yaris. Three quarters of a tank pumping weak heat across the windshield, or a quarter-tank if I dealt with frying my face off instead and used cardboard to redirect the heat up on the windshield. My Jeep I took one night ('87 also, Jeep Comanche w/ 4.0l engine) was the same exact way, quarter tank versus three quarters of a tank idling for 8 hours.

[stran]

Also, I can give a real-world example: Security guard watching a landslide area in your own personal vehicle on a cold night. I've done that before, had to huddle inside my vehicle to stay warm some nights, '87 Corolla FX I had until I bought my Yaris. Three quarters of a tank pumping weak heat across the windshield, or a quarter-tank if I dealt with frying my face off instead and used cardboard to redirect the heat up on the windshield. My Jeep I took one night ('87 also, Jeep Comanche w/ 4.0l engine) was the same exact way, quarter tank versus three quarters of a tank idling for 8 hours.

Out of curiosity, did you unlink the defroster on the Jeep and Corolla? How did you do it?

[jambo101]

Why would anyone disconnect A/C to the defroster mechanism?

There is no faster way to remove moisture from the windows and air then using an A/C. If you don't like the coolness, move the temp control to full heat.

This DIY has to be the most idiotic yet! And for what benefit? Surely not for gas savings, as the savings is insignificant....you really need to fill your time doing something useful, productive, and not devoind of logic, and utility.
I have no problem with the A/C removing moisture from the interior of the car for the first couple of minutes,but once the car is warmed up and windows are clear why do i now need the A/C on when just un A/Ced air from the vents will keep the windows clear. In fact its somewhat of an insult from Toyota to put in this feature as i'm quite capable of pushing the A/C button when i need A/C.

[dybbuk]

An insult? Don't most car manufacturer's do this automatically anyways? All the cars I've ever owned sure have. As Rick said it helps to keep the lawsuits down. Might give this a go, I think I'd unsolder it rather then break it though.

[drt1120]

Though, the knob has a few sticky points. I didn't pay enough attention before to know if I made it stickier or it has always been this way. I can't think of anything I did that would affect the smoothness of the knob.


Thanks for the info on this. I did it a few weeks ago and love not having to run the AC in the defrost mode. I also had the problem with my knob being sticky after I disabled the switch but it turns out that those gears are keyed inside and if you do not line them back up it will stick a every time that smaller gear goes around. Each gear had a notch in it and needs to be lined up to prevent the sticking.

[toast]

Couldn't you save some bother by just pulling the fuse for the a/c or pull the plug off the compressor clutch?

[dreamteam]

I agree with Toast, had the same problem with my defrost, pulled the fuse on the air.
It's clearly marked and easy to get to........liked the results so well, that I pulled the fuse on the wife's '07 corolla. Suddenly, we are both getting better mileage!
Now, this won't work so good if you live in a hot climate........, up here, I won't have to put that fuse back in until spring.

[CTScott]

I agree with Toast, had the same problem with my defrost, pulled the fuse on the air.
It's clearly marked and easy to get to........liked the results so well, that I pulled the fuse on the wife's '07 corolla. Suddenly, we are both getting better mileage!
Now, this won't work so good if you live in a hot climate........, up here, I won't have to put that fuse back in until spring.

People often forget that the A/C is turned on automatically with various settings. Pulling the fuse definitely works as an absolute verification that it is off, but in the case of the Yaris, doing the mod mentioned above definitely turns off the automatic mode, but still lets you turn it manually (without stopping to put the fuse back in).

[Lewis]

WARNING!

I just did this today. I want to warn people who are comptemplating it to leave plenty of time and go very slowly. It is an extremely delicate proceedure and maybe I'm hamfisted but I broke one of the pull out white tabs removing the white piece to get to the curcuit board and had to spot glue it to get it together again so that it was solidly sitting in the holder. The tabs are a very very thin plastic and can snap easily.

Despite the extra bother described above I'm glad I did it because I live in a very damp wooded area and am always running the defroster/defogger. I want to have the choice of engaging the compressor and losing performance and using more gasoline or not engaging the compressor for AC based on whether I judge it's needed in the climatic conditions of the moment. There have been many times a smidgen of heat would have done the trick defogging without AC IMO.

[Lewis]

I just want to take a moment to say THANKS to Stran for doing this DYI. I have run the car two days with this mod and am very happy with the result. One of these days has been cool and drizzly and would have needed the defogger with the compressor running before the mod and now a bit of heat and fresh air on the windschield did the trick saving gas and the bother of turning on and off the defroster constantly to clear the window.

THANKS again Stran!

[yaris-info]

I spoke with the Toyota tech and he said disconnecting the A/C during winter (could be mild winter) is a bad idea. Besides quicker defogging, one of the reasons is to keep A/C compressor running at times, therefore to prolong its life and avoid premature failure.

[stran]

If it's fogging, I turn on the A/C manually to defog quicker. You can also cycle the A/C manually during winter to keep the seals from drying out.

This mod helps you defrost faster. (Frost = ice on the outside)
Also saves gas once you're done the initial defogging.

[darkMINI]

Think of it this way, if you had bought a car with no A/C, would it be any more dangerous to drive in inclement weather simply because it was lacking dryer air? Most of the cars I have owned either had no A/C or it was removed for simplicity or longevity reasons and I have never noticed a problem with defogging. Having the A\C engage automatically every time you want to defrost/defog is similar to believing idiot lights are better than gauges.

[bronsin]

Hmm what about putting in a switch to cut the power to the AC instead of pulling the fuse (or doing the mod maybe)?

The mod sounds tricky so i want to pull the fuse instead.

I doesnt need AC in winter in NJ

But not cycling ac once in a while prolly isnt good for it.

And you might want ac defrost in an emergency even in winter.

Is an ac power disconnect switch easier than the mod or visa versa?

[barryware]

when the compressor is allowed to run based on the status of the A/C switch or the position of the air selector knob, it won't run for long anyway in the winter. The compressor runs and cycles on and off based on refrigerant pressure.

When it is cold out, the compressor may start but because the refrigerant pressure will be too low based on temperature to continue to run, it will shut itself off. I really do not see the need to disable the operation based on the position of the selector knob.

If it is warm enough, you may want the compressor to run and aid in defogging the windows. If it is cold enough and heat alone will do the job, the compressor isn't going to run anyway.

[CTScott]

Hmm what about putting in a switch to cut the power to the AC instead of pulling the fuse (or doing the mod maybe)?

The mod sounds tricky so i want to pull the fuse instead.

I doesnt need AC in winter in NJ

But not cycling ac once in a while prolly isnt good for it.

And you might want ac defrost in an emergency even in winter.

Is an ac power disconnect switch easier than the mod or visa versa?

Adding a switch would be a bit less risky (the risk being breaking the little plastic tabs when taking apart the knob). The switch would simply need to interrupt the light green wire in pin 4 of the 8 pin connector on the back of the knob.

[CTScott]

when the compressor is allowed to run based on the status of the A/C switch or the position of the air selector knob, it won't run for long anyway in the winter. The compressor runs and cycles on and off based on refrigerant pressure.

When it is cold out, the compressor may start but because the refrigerant pressure will be too low based on temperature to continue to run, it will shut itself off. I really do not see the need to disable the operation based on the position of the selector knob.

If it is warm enough, you may want the compressor to run and aid in defogging the windows. If it is cold enough and heat alone will do the job, the compressor isn't going to run anyway.

I find that even in below freezing temperatures that the compressor engages far more frequently than you would expect it to when running in defog mode.

[rick996]

I'm glad bronsin posted to this thread recently. I hadn't seen it before. I just did the tab removal. It took just 10 minutes. I never liked the link of the defroster to the A/C. Thank you stran for posting the original hack (3 years ago). :clap:

[A-Dingo-Ate-My-Baby]

I'm glad bronsin posted to this thread recently. I hadn't seen it before. I just did the tab removal. It took just 10 minutes. I never liked the link of the defroster to the A/C. Thank you stran for posting the original hack (3 years ago). :clap:


I am not sure I understand this. My AC turns on with a button press.

2010 Yaris 5 door US spec with manual temp control knobs.

are you saying that the A/C turns on by itself in certain modes ?
my A/C light will only go on when I press the button

[rick996]

2010 Yaris 5 door US spec with manual temp control knobs.

are you saying that the A/C turns on by itself in certain modes ?
my A/C light will only go on when I press the button

Yes. Whenever you are in one of the 3 defrost modes (full or split). The light doen't come on. All modern cars that I know of do this. It makes the A/C last longer to run the A/C compressor once in a while during the winter. I will put the A/C on manually to accomplish this, but only when I am going down a long hill using DCFO.

[A-Dingo-Ate-My-Baby]

Yes. Whenever you are in one of the 3 defrost modes (full or split). The light doen't come on. All modern cars that I know of do this. It makes the A/C last longer to run the A/C compressor once in a while during the winter. I will put the A/C on manually to accomplish this, but only when I am going down a long hill using DCFO.

holy crap you are right. I just tested it and watched the a/c engage
because I didn't really believe it, and the manual says 'if so equipped' and
since I got an almost rock bottom base model, I was convinced there were no
freebies here. the 4runner always goes to full a/c when you press defog but the
a/c lights up too...yaris doesn't light but compressor certainly starts

[swede]

I tried this mod today, I couldn't believe how easy it was to pull the dash apart to get to it. Everything just popped out and popped back in with ease, no screws or nothing. Just seemed a lot easier than previous cars that I've owned.

anyways I took some pictures and didn't find the wiper arm, maybe somebody can point it out to me. Hopefully the pictures will show it. I have a feeling that maybe I didn't go far enough.

1. Remove dash pieces
2. Pull AC knob out, be careful not to break the tabs
http://i288.photobucket.com/albums/ll191/eahlberg/Yaris/2012-01-01125729.jpg
http://i288.photobucket.com/albums/ll191/eahlberg/Yaris/2012-01-01130017.jpg
3. Pull backing off the unit, again be careful not to break the tabs
http://i288.photobucket.com/albums/ll191/eahlberg/Yaris/2012-01-01130036.jpg
http://i288.photobucket.com/albums/ll191/eahlberg/Yaris/2012-01-01130245.jpg

[swede]

here are some pictures of the micro switch. Didn't have AC in my last car and didn't have too much trouble without it, but I am still considering soldering it off instead of breaking it.




https://lh4.googleusercontent.com/-wD4iXdUSdKY/TwYWo_GGkBI/AAAAAAAAAYA/TFxoECeyQI4/s640/2012-01-05%25252016.28.44.jpg


https://lh3.googleusercontent.com/-jrDBDTeRxDA/TwYWuRTv7aI/AAAAAAAAAYI/FIdAYa83jg0/s640/2012-01-05%25252016.28.20.jpg

[CTScott]

You might as well desolder it, since you are in there. Chances are that you will never bother to put it back, but that way you have the option.

[lilpusher]

hey there people. Yes the ac is a pump and robs power etc. however there is a really good reason it turrns on with the defrost. There is oil suspended in your refrigerant that keeps all those tight clearance parts in your expensive ac compressor running smooth. when your compressor doesn't run for say 8 months of the year the oil seeps down and parts seize up. when the pump blows you get to replace everything at a huge cost the engineers are smart so to prevent you from replacing your ac system every year or so they attached a trigger wire to your defrost to keep things lubed up. cheers.

[A-Dingo-Ate-My-Baby]

hey there people. Yes the ac is a pump and robs power etc. however there is a really good reason it turrns on with the defrost. There is oil suspended in your refrigerant that keeps all those tight clearance parts in your expensive ac compressor running smooth. when your compressor doesn't run for say 8 months of the year the oil seeps down and parts seize up. when the pump blows you get to replace everything at a huge cost the engineers are smart so to prevent you from replacing your ac system every year or so they attached a trigger wire to your defrost to keep things lubed up. cheers.

well let me be the one to say this is BS

The defrost mode goes to A/C, BECAUSE

most people track snow and slush into the vehicle, and in the
winter the inside of a car becomes really humid, and often, ice forms
on the inside of the window as well as the outside in winter.

So, defrost mode activates A/C to assist taking care of this problem
of frost on the inside of the glass.

[bronsin]

True enough moisture inside the car makes trouble and the AC with defrost fixes it fast.

And also I would want to cycle my AC once in a while to keep things lubed for long life.

But having the AC slaved to defrost means running the AC without reason plenty of times.

Which wastes fuel.

Toyota I can decide for myself when to use the AC with defrost thankyou very much.

That goes for all their other idjit "protect the driver from himself" things like ABS, traction control, press clutch to start etc etc etc.






well let me be the one to say this is BS

The defrost mode goes to A/C, BECAUSE

most people track snow and slush into the vehicle, and in the
winter the inside of a car becomes really humid, and often, ice forms
on the inside of the window as well as the outside in winter.

So, defrost mode activates A/C to assist taking care of this problem
of frost on the inside of the glass.

[lilpusher]

chastised on first post, love it. so you've heard of Holden down in OZ right? Bet you $10 the AC pumps in their cars periodically cycle with defrost. Not a lot of snow to contend with down there. BUT ac does indeed help with humidity. Maybe you can enlighten me since I'm new to this model. does the defrost setting on the yaris put the hvac system into recycle as opposed to fresh air?

[rick996]

+1

True enough moisture inside the car makes trouble and the AC with defrost fixes it fast.

And also I would want to cycle my AC once in a while to keep things lubed for long life.

But having the AC slaved to defrost means running the AC without reason plenty of times.

Which wastes fuel.

Toyota I can decide for myself when to use the AC with defrost thankyou very much.

That goes for all their other idjit "protect the driver from himself" things like ABS, traction control, press clutch to start etc etc etc.

[edgardhe]

I did this mod yesterday. It was more tricky than I wanted. I'm pretty new at this though. I tried to desolder the switch and after some fenangling I got it, but I had turned the gears and they were out of alignment for reassembly. I turned the gears until I heard the switch engage and that should have marched the selector at the top of the dial where the defrost turns on. It didn't seem to match though and after a few turns, I heard a crackle and the metal bit of the switch fell out of the assembly. So much for the soldering. Without having to align the switch it was easy to get everything back together once I figured out that the notch on the small gear faces the wall of the assembly. Live and learn. I'm thankful for this forum. I was leaving my car in defrost so the compressor was pretty much running all the time.

[spookybathtub]

Fantastic, thanks so much for posting this! I desoldered the switch and the whole job took about 10 minutes. I wish I had discovered this years ago.