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Old 09-15-2008, 07:02 AM   #1
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A/C Modification Idea

So I still have A/C in my gassaver and I intend to keep it (it gets hot in the south). But I was thinking about how inefficient it is and I concocted a new idea that I need some help with.

The air conditioner sometimes gets too cold when I only need a little cooling. The compressor is cycling on and off quite often, but if I turn it off it gets too hot and if I slide the temp setting on my climate control over, it is simply adding heat and continuing to cycle the compressor just as often (very inefficient).

So I looked in the manual to see what switched the compressor on and off and there is a thermostat set against the coils inside the car. The thermostat is set to cut on if the temp gets above something like 38-41 F and cut back off when it gets down to 32-35 F. (these numbers are estimates because i dont have the manual with me at work, but they are close to give you the idea)

So my idea was to change this thermostat to an adjustable one, or just a higher set one that would require less cycling of the compressor (or just shorter cycles). Say turn on if the temp is above 50-53 and turn off when it gets below 44-47. This would keep the same range as the stock thermostat, but move it up into a more comfortable area, where i could keep the fan on without sliding the temp control away from full cool. And the compressor shouldn't have to work as much, thus increasing FE in the summer time.

Any ideas or suggestions or corrections would be appreciated.
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Old 09-15-2008, 07:16 AM   #2
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Good idea- but it might be easier to put an adjustable thermostat hooked in to the AC on/off button wire- just like an older analog AC thermostat in a house- it would complete the circuit automatically when it got too warn in the car and then open the circuit when it got too cold.

Kinda like having a passenger that turned the ac button on and off as they got too cold /hot
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Old 09-15-2008, 07:50 AM   #3
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Crazy thing about AC in a car is that there is no difference putting the fan blower on Low, Medium, or High. It will all produce the same drag on engine. Therefore what I do is put it on the highest level and hit the AC Button on and off when I get comfortable.

As for the Thermostat. I just did an overhaul on my AC system this past spring and learned a thing or two about the system. The reason they put the thermostat on the system isn't because the air might get too cold for you, but rather because it gets too cold for the system since you don't want the system to run below freezing point... 32*.

Since almost all systems are designed the same way you'll be hard pressed to find a thermostat rated for 50 degrees.
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Old 09-15-2008, 08:34 AM   #4
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Is the a/c really that inefficient?

Isn't one of the claims behind HHO that it works the engine harder so it gets into a more efficient operating range? Why doesn't that work with the a/c system?
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Old 09-15-2008, 08:52 AM   #5
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I like the idea of using a bimetal thermostat (mercury thermostats won't work in a car) to control the a/c clutch. Just cut the a/c clutch wire and extend it to the interior, and run it through the bimetal thermostat. The fan will run all the time, but the compressor will only run when it gets too warm inside.

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Old 09-15-2008, 09:28 AM   #6
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How about this DIY thermostat?

http://www.apogeekits.com/thermostat.htm

This would be a low-budget DC thermostat that could work. I may just have to order one if the conscensus is that an adjustable air temp thermostat spliced into the a/c activation line would work.

I don't think that splicing in at the clutch would work because most cars also have a method of increasing the engine's bypass air to maintain an idle speed and if the clutch doesnt engage and the idle air control valve opens then the rpms will jump up and waste fuel.

I could pull the plug from the stock thermostat and wire to the adjustable unit (just leave the stock thermostat in and disconnected). No wire cutting necessary and i could always plug the stock one back in.

Thanks for the input so far.
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Old 09-15-2008, 10:14 AM   #7
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Ok, then have the thermostat control a DPDT relay. The relay will cut the power to the a/c clutch and the a/c idle solenoid. The only problem I see with this is that it may cause surging and an irregular idle at times.

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Old 09-15-2008, 10:19 AM   #8
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Now hold up. You might not have to do all of that.

Try this. Go to the clutch and disconnect it. Then turn the ac on and see if the idle speeds up or not. Most cars won't idle up if the clutch is disconnected.
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Old 09-16-2008, 03:09 PM   #9
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You may run into a problem of the car fogging up if you mess with the thermostat. The coils are kept between the factory set temps so the water continues to condense on them. If you let them warm up too much the sudden rise of humidity on the inside of the car could cause the surfaces to fog.


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Old 09-17-2008, 03:24 PM   #10
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I cannot even do a simple mod, so I try to act as my own thermostat. I switch on the AC button when it is hot, and switch it off when it is cold. For the Matrix, it is just a light tap on the AC button for on or off.
However, I make it a habit to switch the AC off and turn the fan power to maximum about 5 minutes before a trip ends so as to save fuel. The car can usually remain comfortable enough for a short period like that. For short trips, I don't use the AC at all. It takes time for the AC to cool the car down anyway.
A by-product is that no foul smell will come out of the ventilation the next day when the car is started because my practice helps keep the vents dry and prevent the growth of smelly fungi inside them. After I switch off the AC in that manner each trip, a strong draft still keep blowing through and out of the vents to keep people comfortable and dry up the moisture in the vents.
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