Engine Fan - AC - Thanks
 

Hi everyone,

3 month ago, in another thread, I was posting about how my engine fan is going all the time with no reason.

I Have a Toyota Matrix 2013.

NoD~ told me that my AC should be ON. Because it's turned on automaticly just by using the defrost. I was not even listening to that advice because it seemed silly. After some test ... I can insure you that that NoD~ is in the truth.

In my Toyota, If I push air in my windshield, AC is kicking-in without noticed. Which mean that last winter, I had my AC running ALL the time.

Why do I need to run AC during winter? Heater is not enough to remove humidity?

Any way, my next mod is to find a way to be able to blow hot air in my windshield without involving the AC

Also thanks to every member of this forum that is taking the time to formulate complete and clear answers.

The defrost setting is really for fog on the windshield and side windows. A/C is activated because the A/C can very quickly remove moisture from the car in the car which is what causes the fog in the first place.

If you don't actually have an A/C button to deactivate the compressor while you are trying to de-ice your windshield, then just turn the heat setting to full hot and it will still blow out hot air. On some modern cars you don't have a choice as to whether your A/C compressor gets selected or not. On my older Civic it automatically turns on but I can manually hit the A/C button and turn it off if it's winter and I am de-icing the windshield.

Pull the A/C relay, or wire in a disabling switch or something like that would be easiest I would think.

cbaber,

In my Matrix, the AC is kicking in without any king of noticed. I cannot press a button to disabled it.

I will do something like what Doax is suggesting and put another switch to kill that AC when needed.

Hopefully next winter I will have a better Fuel Millage!

Side note, for the tags of the thread, is it possible to write 2 letters words. "AC" would make a lot of sence.

There is likely a wire plug on the A/C compressor that you can hook and it will cut power, disabling the A/C.
To make the A/C work again all you have to do is put the plug back where it goes.

keep in mind, doing this MAY or may not trigger a SES due to the compressor not running when the PCM is expecting it to.

IMO, the better(though much more involved on some vehicles) option would be to intercept the signal that the HVAC module sends to the PCM to indicate that the compressor should be running. some vehicles, this can be done by opening the circuit with a rocker/toggle switch. your HVAC module will still command the blend door(s) and routing door(s) to where you set them to, but the PCM won't try to turn the compressor on.

i have no idea how a 2013 toyota's HVAC module handles the compressor request though, probably over a datastream if i had to guess.

In any event disabling should be possible by taking out the relay which drives the clutch on the compressor.
Take that out and it'll be like compressor is off.
But you might need it to defog, so, for the coil side of the relay, wire a switch back to say the glovebox where you can disable the relay coil being energised.

I pull the fuse for the A/C circuit in my ranger after summer is over, but I do put it back in about once every 2 months to run it for a few minutes (resale value you know)

The reasoning behind running the A/C is sound. At a given temperature air is capable of holding a certain mass of water. Drop below that temperature and the water condenses out. (This is why it rains or snows.) Precooling the air before reheating dries the air by allowing the water to condense out on the A/C evaporator core and drain from there to outside the car. That makes the defrosting more effective.

Disabling it at the relay that switches the A/C clutch will be easiest. It is possible to connect through the brake light switch (or an additional switch) and still have the A/C, essentially for free. There does need to be some hysteresis in the switch or the cycling can be too rapid, such as when a brief brake application is used.

A warning though: the brake switch may be an input into a body control module and not switching the brake lights directly which will affect how you can wire it.

If there is an issue with the on board computers expecting A/C on and not getting it, there should be an evaporator temperature sensor that cuts out the A/C to prevent the evaporator freezing. Emulating that signal as 'cold' would prevent the compressor being switched on.

this is true.... an A/C system that isn't in use does tend to have problems once it starts to get used again.