Manually control a/c compressor with defrost on

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Old 14 Apr 2015, 11:00 am   #1 (permalink)
Bob Simon
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Default Manually control a/c compressor with defrost on

2012 Prius C, Trim Level 3

I would like the ability to keep the windshield defrost button engaged for the duration of a trip while manually cycling the compressor on and off at will. I presume the best way to do this involves overriding the signal to the compressor relay. Please advise how this can be done or suggest a better approach.

If the modification involves working with an IC, I will need the exact location of the device. Please also include the part # and names of the signalpins I need to work with if you have them.

This will be my first mod to my car but I have steady hands and an adjustable power soldering pencil.

Thanks!
Bob Simon
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Old 15 Apr 2015, 06:48 am   #2 (permalink)
Elmo P. Shagnasty
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Default Re: Manually control a/c compressor with defrost on

In article <d6caf336-77a4-41f7-8591-5d7b2e0b998c@googlegroups.com>,
Bob Simon <bobneworleans@gmail.com> wrote:

> I would like the ability to keep the windshield defrost button engaged for
> the duration of a trip while manually cycling the compressor on and off at
> will. I presume the best way to do this involves overriding the signal to
> the compressor relay. Please advise how this can be done or suggest a better
> approach.


ummm.....you're WAY overthinking this.

Don't worry about the windshield defrost button. Just manually control
the climate system. Turn the temp to where you want it, turn the
airflow to where you want it (in this case the windshield), and turn the
AC button on and off at will.

You DID read your owner's manual, right?

Why did you immediately go to soldering onto a circuit board???
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Old 15 Apr 2015, 01:39 pm   #3 (permalink)
Bob Simon
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Default Re: Manually control a/c compressor with defrost on

On Wednesday, April 15, 2015 at 5:48:58 AM UTC-5, Elmo P. Shagnasty wrote:
> In article <d6caf336-77a4-41f7-8591-5d7b2e0b998c@googlegroups.com>,
> Bob Simon <bobneworleans@gmail.com> wrote:
>
> > I would like the ability to keep the windshield defrost button engaged for
> > the duration of a trip while manually cycling the compressor on and offat
> > will. I presume the best way to do this involves overriding the signalto
> > the compressor relay. Please advise how this can be done or suggest a better
> > approach.

>
> ummm.....you're WAY overthinking this.
>
> Don't worry about the windshield defrost button. Just manually control
> the climate system. Turn the temp to where you want it, turn the
> airflow to where you want it (in this case the windshield), and turn the
> AC button on and off at will.
>
> You DID read your owner's manual, right?
>
> Why did you immediately go to soldering onto a circuit board???


Elmo, thanks for the reply. It is possible that there's a better way to dowhat I want but your suggestion does not do it.

There isn't an option to set the air flow to both head + windshield on my system. Airflow toggles between head, head + feet, feet, feet + windshield.I've been doing something like what you suggest by setting the airflow tohead then intermittently pressing the defrost button when the windshield is cloudy and un-pressing it when it's clear. But that does not keep the windshield damper open when defrost is off, which is what I'm trying to fix.

Also, although I have not verified this by checking under the hood, it seems to me that when I have defrost on, the compressor runs continuously because it is ALWAYS blowing cold. The AC button doesn't have any noticeable affect at all. If I turn up the temperature knob, the air is heated before delivery but I presume that the compressor is still on.
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Old 15 Apr 2015, 04:12 pm   #4 (permalink)
Le Forgeron
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Default Re: Manually control a/c compressor with defrost on

Le 15/04/2015 19:39, Bob Simon a écrit :
> On Wednesday, April 15, 2015 at 5:48:58 AM UTC-5, Elmo P. Shagnasty wrote:
>> In article <d6caf336-77a4-41f7-8591-5d7b2e0b998c@googlegroups.com>,
>> Bob Simon <bobneworleans@gmail.com> wrote:
>>
>>> I would like the ability to keep the windshield defrost button engaged for
>>> the duration of a trip while manually cycling the compressor on and off at
>>> will. I presume the best way to do this involves overriding the signal to
>>> the compressor relay. Please advise how this can be done or suggest a better
>>> approach.

>>
>> ummm.....you're WAY overthinking this.
>>
>> Don't worry about the windshield defrost button. Just manually control
>> the climate system. Turn the temp to where you want it, turn the
>> airflow to where you want it (in this case the windshield), and turn the
>> AC button on and off at will.
>>
>> You DID read your owner's manual, right?
>>
>> Why did you immediately go to soldering onto a circuit board???

>
> Elmo, thanks for the reply. It is possible that there's a better way to do what I want but your suggestion does not do it.
>
> There isn't an option to set the air flow to both head + windshield on my system. Airflow toggles between head, head + feet, feet, feet + windshield. I've been doing something like what you suggest by setting the airflow to head then intermittently pressing the defrost button when the windshield is cloudy and un-pressing it when it's clear. But that does not keep the windshield damper open when defrost is off, which is what I'm trying to fix.
>
> Also, although I have not verified this by checking under the hood, it seems to me that when I have defrost on, the compressor runs continuously because it is ALWAYS blowing cold. The AC button doesn't have any noticeable affect at all. If I turn up the temperature knob, the air is heated before delivery but I presume that the compressor is still on.
>


Of course you know how windshield demist (not defrost) is supposed to
work, don't you ?

For the innocents:
==================

The air is cooled to have it condense any extra humidity, liquid water
is collected and throw away, then cooled air can be heated back a bit:
hotter air have a greater acceptance for water (heating cooled air makes
it dry if it cannot take back the water that went liquid during
cooling), so when meeting the windshield, the mist (condensed water on
glass) is transferred to the air (as invisible vapour), thus demisting
the windshield.



What you are asking (stop the compressor on demand, while demisting) is
a scientific non-sense. It can work a few moments, playing on the
inertia of the cold block, but on the long run it will just fail to
demist, as wet air to the windshield will not remove the current liquid
water (the white mist) from it, it might even provide more. (as the
windshield is exposed to external wind... it become the coolest place,
and that's where water in the inside air will condense).

If the outside of the car is a rainy tropical forest, you might consider
using closed-loop AC/demist instead of open-flow intake.
It might be wise considering too when inside a large mist like SF
sometime have. In the closed-loop situation, once demisted, the living
bodies inside the car are the only source of additional mist: you could
probably, once windshield is clear, just stay in AC mode (so no full
time compressor). The more passengers, the more humidity.


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Old 16 Apr 2015, 12:53 am   #5 (permalink)
bwilson4web
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Default Re: Manually control a/c compressor with defrost on

Hi Bob,

On Tuesday, April 14, 2015 at 10:00:08 AM UTC-5, Bob Simon wrote:
> 2012 Prius C, Trim Level 3
>
> I would like the ability to keep the windshield defrost button engaged for the duration
> of a trip while manually cycling the compressor on and off at will. I presume the best way
> to do this involves overriding the signal to the compressor relay. Please advise how
> this can be done or suggest a better approach.


I know how to find out. Toyota has a technical information service:
https://techinfo.toyota.com/techInfo...pmanager/t3/ti

With this service, you can register and pay for access to the shop manuals for your car. Download the schematics and parts of the shop manual that apply to your prius and the problem is solved.

You might also visit PriusChat.com, the Prius c forums. The moderators are very skilled at keeping the 'trash talkers' out. Best of all, you'll be working with folks who own your model car and walk out to the car to see what is there. Registration is free at PriusChat.com

GOOD LUCK!
Bob Wilson

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Old 16 Apr 2015, 06:01 am   #6 (permalink)
Elmo P. Shagnasty
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Default Re: Manually control a/c compressor with defrost on

In article <841509b6-95ac-4f36-9652-0aa896679098@googlegroups.com>,
Bob Simon <bobneworleans@gmail.com> wrote:

> But that does not keep the windshield damper open when defrost is off, which
> is what I'm trying to fix.


Huh. Well, how about simply mechanically rigging the damper such that
air always flows onto the windshield? Don't know if you can do that,
but if so it may be simpler than messing with the electronics.



> Also, although I have not verified this by checking under the hood, it seems
> to me that when I have defrost on, the compressor runs continuously because
> it is ALWAYS blowing cold. The AC button doesn't have any noticeable affect
> at all. If I turn up the temperature knob, the air is heated before delivery
> but I presume that the compressor is still on.


Well, by definition "defrost" means "remove moisture"--and the removal
of moisture (not cooling) is why the air conditioning compressor is
there in the first place. To defrost, one must first start with dry air.

To mitigate the cold effect that comes with removing moisture, one can
add heat back to the dry air--which is what the system does.

I guess Toyota never considered that anyone would want air on the
windshield for general purposes--that any air directed to the windshield
is overall intended for the purpose of removing moisture from the
windshield.

Ergo, I keep going back to the mechanical solution--can the door that
diverts air to the windshield be rigged or removed such that air always
goes to the windshield regardless? Would that solve the problem?
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Old 16 Apr 2015, 01:55 pm   #7 (permalink)
Bob Simon
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Default Re: Manually control a/c compressor with defrost on

> What you are asking (stop the compressor on demand, while demisting) is
> a scientific non-sense. It can work a few moments, playing on the
> inertia of the cold block, but on the long run it will just fail to
> demist, as wet air to the windshield will not remove the current liquid
> water (the white mist) from it, it might even provide more. (as the
> windshield is exposed to external wind... it become the coolest place,
> and that's where water in the inside air will condense).


I disagree. I expect that ambient air moving across the windshield will do some good for at least 15 seconds, which is my desired minimum on or off duration.
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Old 16 Apr 2015, 01:57 pm   #8 (permalink)
Bob Simon
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Default Re: Manually control a/c compressor with defrost on

On Wednesday, April 15, 2015 at 11:53:18 PM UTC-5, bwilson4web wrote:
> Hi Bob,
>
> On Tuesday, April 14, 2015 at 10:00:08 AM UTC-5, Bob Simon wrote:
> > 2012 Prius C, Trim Level 3
> >
> > I would like the ability to keep the windshield defrost button engaged for the duration
> > of a trip while manually cycling the compressor on and off at will. I presume the best way
> > to do this involves overriding the signal to the compressor relay. Please advise how
> > this can be done or suggest a better approach.

>
> I know how to find out. Toyota has a technical information service:
> https://techinfo.toyota.com/techInfo...pmanager/t3/ti
>
> With this service, you can register and pay for access to the shop manuals for your car. Download the schematics and parts of the shop manual that apply to your prius and the problem is solved.
>
> You might also visit PriusChat.com, the Prius c forums. The moderators are very skilled at keeping the 'trash talkers' out. Best of all, you'll be working with folks who own your model car and walk out to the car to see what is there. Registration is free at PriusChat.com
>
> GOOD LUCK!
> Bob Wilson


Bob,
Thanks for the useful reference. Since this project will be a stretch for me, I'd like to like up some potential technical assistance. Are you awareof a newsgroup where Toyota electrical mods are discussed?
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Old 16 Apr 2015, 01:59 pm   #9 (permalink)
Bob Simon
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Default Re: Manually control a/c compressor with defrost on

On Thursday, April 16, 2015 at 12:57:49 PM UTC-5, Bob Simon wrote:
> On Wednesday, April 15, 2015 at 11:53:18 PM UTC-5, bwilson4web wrote:
> > Hi Bob,
> >
> > On Tuesday, April 14, 2015 at 10:00:08 AM UTC-5, Bob Simon wrote:
> > > 2012 Prius C, Trim Level 3
> > >
> > > I would like the ability to keep the windshield defrost button engaged for the duration
> > > of a trip while manually cycling the compressor on and off at will. I presume the best way
> > > to do this involves overriding the signal to the compressor relay. Please advise how
> > > this can be done or suggest a better approach.

> >
> > I know how to find out. Toyota has a technical information service:
> > https://techinfo.toyota.com/techInfo...pmanager/t3/ti
> >
> > With this service, you can register and pay for access to the shop manuals for your car. Download the schematics and parts of the shop manual thatapply to your prius and the problem is solved.
> >
> > You might also visit PriusChat.com, the Prius c forums. The moderators are very skilled at keeping the 'trash talkers' out. Best of all, you'll beworking with folks who own your model car and walk out to the car to see what is there. Registration is free at PriusChat.com
> >
> > GOOD LUCK!
> > Bob Wilson

>
> Bob,
> Thanks for the useful reference. Since this project will be a stretch for me, I'd like to like up some potential technical assistance. Are you aware of a newsgroup where Toyota electrical mods are discussed?


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