It seems that when I switch fan to windscreen, my A/C is forced on although the A/C button & light is off.

I wish it to be possible to disable A/C while blowing air to windscreen. It does not bother too much on summer, but it means that you have to run A/C constantly in the winter to keep your windows clear.

Usually I just run A/C a while after start in the winter to get the windows cleared out quick and then turn it of to save some gas.

Has anyone experienced the same, or is there something wrong with my controls? Any clues how I can go a round it?

Thanks,

3xJ

I haven't experienced this in the Patriot yet...still playing with this puppy and learning its tricks. My Ford Focus would do the same thing - turn on the A/C when set to Defrost, but the A/C light went on.

It is my understanding that the a/c will go on when in defrost mode unless the temperature is below 55 degrees Fahrenheit. That is not from reading the current owners manual but from several older cars.

i have not noticed this, but i guess i have not ever paid that close of attention.

Just tried windscreen setting this evening, and indeed the A/C started up without the A/C button light coming on.

Most Japanese cars do this, and can be fixed with a relay change. Not sure anything like this is out there for the Patriot/Jeeps yet.

It kicks the AC on in defrost mode to help dry things out. What's even more irritating about it is that (at least in my SE-R) if you legitimately needed to use it on defrost, leave it that way and turn off the car and come back to it whenever- you start it up and it's still on defrost you can't get the AC off until you shut the car off again and turn the fan to another position.

The manufacturer's indeed do this to dry the air being blown on the windshield. Since you are trying to remove moisture (frost/condensation/mist) from the inside of the windshield, it will work much faster to use air that has been dried (conditioned).

Ever notice the drip from the firewall during the summer? That is the humidity that has been removed from the incoming air. Since the moisture also holds heat, when it is removed, the temperature of the air drops significantly, which is the now cooled air blown in by the air conditioner.

The practice of using the A/C while defrosting (even in winter) began decades ago: since many people would not use the A/C from, say, October til late April, the seals in the A/C system would dry out, and begin to leak the refrigerant. Many people would have to buy a can of Freon (R12-the old stuff) to top off the system every spring. So, the mfgrs began to use the A/C system to dry the air for defrost purposes, which also kept the seals lubricated so the system would remain leak free.

Net result: better demisting/defrosting, fewer system repairs over several years, and less environmental pollution from unnecessarily leaked refrigerant.

Don't know why you would want to develop a bypass for this (except for better mpg). Easiest way around it is to manually turn off the defroster as soon as the windshield is clear - there is no need to have it on if you are not trying to demist the windshield. Also, use RainX AntiFog, and you will rarely have moisture on the inside of the windshield.