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Old 11-19-2008, 08:30 PM   #1
stran
 
Drives: '07 Yaris 3D HB Auto
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Thumbs up DIY: Unlink A/C from Defroster

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/sho...light=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.
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Old 11-20-2008, 10:53 AM   #2
IllusionX
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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.
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Old 11-20-2008, 12:02 PM   #3
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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?
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Old 11-20-2008, 12:51 PM   #4
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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.

Last edited by echo_hrs; 11-24-2008 at 07:56 PM. Reason: ...
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Old 11-20-2008, 01:23 PM   #5
stran
 
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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.
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Old 11-20-2008, 07:09 PM   #6
IllusionX
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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.
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Old 11-24-2008, 06:44 PM   #7
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Can you manually turn on the A/C with the button when in defrost mode "after" the mod?
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Old 11-24-2008, 09:24 PM   #8
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Can you manually turn on the A/C with the button when in defrost mode "after" the mod?
yup.
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Old 11-25-2008, 09:54 AM   #9
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push the AC button :rofl:
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Old 11-25-2008, 05:15 PM   #10
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Quote:
Originally Posted by IllusionX View Post
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).
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Old 11-25-2008, 05:26 PM   #11
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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.
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Old 11-25-2008, 08:42 PM   #12
IllusionX
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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...


Quote:
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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.
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Old 11-26-2008, 04:29 PM   #13
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yup.
thanks, I didn't see any reason why it wouldn't but just wanted to ask since this is a one-way mod.
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Old 11-26-2008, 08:50 PM   #14
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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.
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Old 11-28-2008, 06:55 PM   #15
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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.
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Old 11-28-2008, 07:57 PM   #16
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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.
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Old 11-28-2008, 09:11 PM   #17
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Originally Posted by SilverGlow View Post
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.
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Old 11-29-2008, 03:32 AM   #18
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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?
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