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Discussion Starter #1
I had a look through the "mod" forum but couldn't see this one.. so maybe it has been done, maybe not.
I find when I'm driving a vehicle with air conditioning, and am tempted to use it, I try to just enable it just when going down steep hills, that's often enough to keep the car cool. Of course the insight has an effective regen system, but any time the brake pedal is being pressed, there's energy being wasted :)
So I was wondering about having the brake light switch connected to a normally-open relay in series with the AC pump clutch. Of course, you would want an extra switch to put the operation back to normal..

Worth bothering with? I may try it..
 

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I like it! That would great for us in the deep south, hot & humid.

Great idea.

Will you let us know the results?
 

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It's a good idea. I always thought it would be good to have the AC have an "econ" mode where the AC only runs when the car is either coasting or braking, I tend to just switch the AC in my civic on and off manually in these cases. For coasting down hills the AC is nice, it can provide just enough exrtra drag to keep the car in control without downshifting further or applying more brake pressure where I live.
 

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It is would be a bit more work, but you could use a vacuum switch plugged into the intake manifold. Then the A/C compressor only engages when you lift off the gas. You might need a relay and of course a bypass switch mounted inside.
 

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Discussion Starter #5
Thanks for the feedback and ideas.. from what you're saying, perhaps off-throttle AC would be a benefit too (of course it's "stealing" some regen opportunity..?). It's sounding like another feature for MIMA_C almost :)

In the meantime, the suggestion of a vacuum operated switch is a good one, or maybe a simple microswitch to detect "gas pedal completely up".

It might be a while before I get around to trying it so if anyone else wants to give it a go, please do!
 

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The only problem with this idea is the cycling of the A/C system so frequently is not good for it in the long run.
 

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Discussion Starter #7
Resist said:
The only problem with this idea is the cycling of the A/C system so frequently is not good for it in the long run.
In what way? Surely the compressor cycles on and off all the time, to maintain the temperature. All this mod would do it prevent it cycling on when the accellerator is pressed..
 

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This reminds me about my previous car.
The 1998 Subaru Legacy GT turns off the AC automatically during hard or medium acceleration, but my Insight with high tech super duper electronic everything 10x the computer power required to travel to the moon does not turn off the AC when accelerating! :evil:
The AC affects the acceration of the Insight so much that some might consider this a safety hazard.
This feature along with those mentioned by others above would be awesome to include in the next generation of MIMA if possible.
 

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kalmar said:
In what way? Surely the compressor cycles on and off all the time, to maintain the temperature. All this mod would do it prevent it cycling on when the accellerator is pressed..
Oh I see, then maybe I misunderstood what was stated.
 

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Guillermo said:
The AC affects the acceration of the Insight so much that some might consider this a safety hazard.
A safety hazard? This is a rather long stretch to be considered a safety hazard. Yes there is a slight decrease in performance due to the A/C, as there is in any car. But a simple press of a button returns that performance when needed. It certainly isn't enough of a loss to cause a safety concern.
 

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kalmar said:
Resist said:
The only problem with this idea is the cycling of the A/C system so frequently is not good for it in the long run.
In what way? Surely the compressor cycles on and off all the time, to maintain the temperature. All this mod would do it prevent it cycling on when the accellerator is pressed..
While true the A/C does cycle all of the time...it is a more rhythmic cycle.
Tapping the brake (electric switch) or accelerator (vacuum) a few times
within 20 seconds (like when in traffic) cannot be good for the compressor.

If there was a timing circuit in place to only allow the A/C on after say
30 seconds between brake applications should allow a safety factor.

I have thought about this type of mod as well as I also try to use the A/C
more when going downhill.

Another thought would be an incline (downhill) sensor (mecury switch??)
with the timing circuit and relay could be used as well... Why let off the
gas or use the brake if you don't have to?....


Without the timing circuit, I agree with Resist on this one...

JoeCVT - Just your average CVT owner
 

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I believe that the cycling of the compressor is quite frequent as it is. Further, cycling of the compressor does not put any strain on it. The only component that might incur wear from this would be the clutch on the compressor. Even in this case, you are looking at one application when you brake, which will likely occur possibly once every minute or more. Tapping the brake repeatedly within a short period, as has been implied, does not seem a very realistic braking scenario.

Having said that, I'm on the other side of the "throttle completely up" issue. I hate the way the car tries to regenerate when no throttle is applied, as it means I have to choose between coasting in neutral, using gas at idle, or coasting in gear, using no gas (fuel cut mode) but coasting a much shorter distance. I would not want the AC to stifle the time spent in fuel cut that I do have. AC on during braking is something I would favor, as it would reduce wear on the brake system and it wouldn't waste energy.
 

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The compressor is designed to be of the clutch cycling type so little or no extra wear will occur except in some type of repeated abnormal brake pedal fluttering.

However, what this thread so far seems to miss is that the effective on time will be insufficient for adequate cooling in almost all foreseeable scenarios.

Guillermo's got the ticket :!: :)

From wayyyy back in the 70's, one of the few EPA proven "gas saver" devices was a vacuum switch wired in series with the A/C compressor clutch. It was proven in the city drive cycle a 5-7% MPG improvement was realized if the A/C compressor was cycled off on _acceleration_.

This was a feature incorporated in the Insight's predecessor the CRX HF. The PCM has full control of the compressor clutch the "acceleration" logic was built-in.

Haven't done the test on the Insight to see if its also in there.

HTH! :)
 

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The shop manual page 21-79, where it tells how to diagnose the A/C clutch not engaging problem, mentions that the throttle position sensor voltage needs to be be within a certain range. So I suspect that the system does in fact cycle off under heavy acceleration.

Since it also knows about the application of the brakes, it's possible that it could run the compressor for extra braking power, too. Has anybody put a little test light on the compressor relay to find out for sure?
 

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Tapping the brake repeatedly within a short period, as has been implied,
does not seem a very realistic braking scenario
I'm talking about driving in heavy highway traffic where one nervous
person in front repeatedly puts on the brakes and others following put
on the brakes as well....I wasn't suggesting that you just tap the brakes
for fun. I was using the brakes as the example but this also applies to
the idea of lifting off the throttle repeatedly as well.

I like the idea as a whole but I would try to add some method to make
sure it does not cycle quickly with every foot action (brake or gas).

JoeCVT - Just your average CVT owner
 

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joecvt said:
I'm talking about driving in heavy highway traffic where one nervous person in front repeatedly puts on the brakes and others following put on the brakes as well...
Ah, easily alleviated by not riding the bumper of the car in front of you. ;)
 

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i like to keep track of whats going on with the car. when i converted my jeep to fuel injection i added 3 LEDs to the efi system to keep track of the different operating modes. i plan to put a blue LED on the dash to see when the a/c compressor is on.

andy g.
 

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Insightful Trekker said:
From wayyyy back in the 70's, one of the few EPA proven "gas saver" devices was a vacuum switch wired in series with the A/C compressor clutch. It was proven in the city drive cycle a 5-7% MPG improvement was realized if the A/C compressor was cycled off on _acceleration_.
Anyone know where to get an automotive vacuum switch? i have checked a couple junk yards and they don't know what i'm talking about. approx $65 for a new McMaster or industrial switch.

I used to have one of these vacuum switches on my 77 plymouth volare with a slant six with a 4 barrel holley carb and a 4 spd.
 
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