Re: 2002 Caravan defroster

No way to turn it off other than un plugging the A/C compressor.
It's for your own safety. It goes a long way to help prevent window
fogging.
And yes, it does take more gas...

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It's important to keep in mind that there is a temperature sensor on the evaporator of both of these vehicles that will not alow the A/C to engage at any temperature that would cause the system to freeze up. So your -25 scenario is a non issue. Even though the system is asking for the A/C to be on the sensor won't let it below approx 32 F.

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Sam Man wrote:

So 'splain to me why the A/C came on in just those circumstances on the '95.
Dan
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Another stupid button that for 99% of drivers will get left permanently in the "cancel" position.
I remember reading about this "turn on A/C when defrost is on" feature back in the 70's on GM vehicles, I think. It was stupid then and is still stupid today. The only time it significantly shortens the defog time is when the car is cold and the coolant temp is low and the air temp is above freezing.
The controls need to be designed so that the A/C can be optionally switched on during defog, by the driver. Then, the minority of drivers that would see any benefit can make use of it, and the rest of us can just wait until our car warms up.
Ted
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It could come on under certian conditions in cold weather if you're sitting still and you get a slug of hot air from the engine box that is recirculated into the HVAC opening which would cause the sensor to read high.
Ted: It'll never be made an end user feature since it would drive up warranty and JD Power numbers for window fogging complaints when people forget to turn it back on....

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Hi Sam Man,
Thanks for your thoughts but I must diagree about the safety benefits of having A/C during defrost.
Here in New England during times of fairly cool days and high outside humidity, having the A/C on during defrost causes the OUTSIDE of my windshield to fog up due to the drop in glass temperature. Then I have to run the windshield wipers in order to see and/or add enough heat to reheat the glass making the interior temperature rise to the uncomfortable level. Overall, it's a ridiculous situation that also wastes energy and drops fuel mileage. I've see to A/C come on during defrost down to about 50 degrees F - well below the temp needed to start outside frosting of the glass.
Since all HVAC functions are controlled by software in the control module, I'm sure that it can be reprogrammed to stop this function. However, it may well take the use of the dealer programming device and someone who knows the software coding to do it. Obviously, unplugging the compressor is an alternative but not the ideal one. Once my warranty expires I may well add a switch.
Doug
wrote:

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It is the accepted best practice of the industry. Of course there are always some conditions which could be compromised by the strategy. We have discovered that this strategy benifits the majority of our customers...

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