preventing AC from coming on when using defogger

[whiterabbit]

Is there a way to keep the AC from kicking in when you use the front defogger?

[Mulder]

Info here:
http://forums.nasioc.com/forums/show...hreadid=148118
You're welcome

[samowrx]

i've never noticed if the ac tunes on in my car with the defrost. i don't think it does. the ac light doesn't light up.

[Mulder]

It does, there is a microswitch that is activated when the mode dial is moved to the defrost position and turns on the compressor. The light in the AC switch won't come on unless you push the button but the compressor still runs in defrost mode. If you do the mod in the linked thread the compressor will be fully independent and only controlled by the button.

[Chunky_Chicken]

The AC comes on for a reason, defeating it will dramatically reduce your defroster's effectiveness.

Your window fogs when there is enough moisture inside the car to cause condensation on your colder window. Its called the Dew point.

Your defroster needs 2 things to work properly. It needs to be drawing air from the outside (not recirculating the moist stagnant air from the inside) and it needs the AC on. By running the incoming air through the super cold evaporator you're causing the moisture which would have condenced on your windscreen to condence earlier on the evaporator coils. Thats why you see AC systems dripping water under the car on hot days.

Turning the AC off is gonna let this moisture make it to your windshield, where its gonna inhibit your view.

-Pete

[Mulder]

You're right Chunky, the idea of the mod is not to defeat this function totally but to allow driver control of when the compressor comes on. There are some conditions when just blowing air through the defroster vents will clear the window, and for those times running the AC is a waste. When it's needed the AC can still be used for defrost by pushing the switch. Many cars come from the factory this way so you have the choice of whether to use the defrost mode w/ or w/o AC.

[Snowphun]

Exactly, I'm smart enough to determine if I want the AC on or not. Lots of other cars allow you to make this choice on your own.

[WRXVT]

Hey, does the A/C kick on when you have it on the defog/floor setting? I am talking about the second to last setting on the vent controller thing, I know it kicks on when its on the last setting (defrost) but was curious about the other defrost/floor setting.

Also, does anyone know if the a/c sucks less power when the fan setting is low? Like if the fan is on 1, is the a/c running less hard than if the fan is on 3 or 4?

[FutureWagon]

Originally posted by WRXVT
Also, does anyone know if the a/c sucks less power when the fan setting is low? Like if the fan is on 1, is the a/c running less hard than if the fan is on 3 or 4?

No, the fan setting has no DIRECT bearing on how HARD the a/c runs, it IS directly related to how OFTEN the a/c compressor clutch turns on/off (based on my limited knowledge of the way a/c systems work). Since the a/c belt is always spinning when the engine is turned on, there is an electrical clutch on the compressor. When you turn the a/c on, the clutch engages, compressing the refrigerant.

The compressor pumps the refrigerant; the refrigerant goes to the condenser (radiator-looking thing next to the engine coolant radiator) to SLIGHTLY cool off the hot compressed refrigerant; then to a heat exchanger in the dash; the pressure drop in the heat exchanger (evaporator?) causes the refrigerant to get REALLY cold; the climate control fan blows air over the heat (actually cold) exchanger; cold air comes out vents; refrigerant goes back to compressor. There's a thermometer in the heat exchanger, so the more you warm up the cold part in the dash by blowing air over it, the more often the compressor clutch is engaged, using available HP from the crank.

...I think...

[whiterabbit]

i cant find the purple wires to cut. pics? description?

thanks

here is the coressponding thread with how to...
http://forums.nasioc.com/forums/show...hreadid=148118