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Originally posted by Biper on MSV


Cost: $5
Time: 1-2 hours
Parts:
1 single pole double throw (SPDT) switch
50cm (18in) small gauge (~24 AWG) wire
10cm (3in) of heat shrink tube OR black electrical tape
Tools:
Wire cutters
Soldering Iron
Drill

When driving my 2002 Sentra, it would bother me to no end when the front windows started to fog up because this meant turning on the front defog fan. That alone is fine, it’s the fact that the A/C compressor turns on with the fan that burns. It steals powers and it uses extra gas, no thanks!

Now those of you who want to banish this demon to the far corners of hell can find that “how to” elsewhere. For those of you that like the convenience of having their windows defrost quickly in the morning and want to turn the compressor off after that then this mod is for you.

Preparation:

Cut the wire into three equal-length parts. Solder them to the three terminals on the switch. Shrink wrap or tape up terminals.

NOTE: this mod involves adding a switch near the instrument cluster. If you want to put it somewhere else then add extra wire accordingly!

The job:

Start by popping out the centre console and trim piece that surrounds the environment controls.

Next remove the radio.

Locate the two black wires running into the back of the cabin zone switch (see picture)




Free up the wires by looping them under the tie-down tab. The above picture show one of them free. Cut one of the two wires (doesn’t matter which) and splice in the switch. Make sure the center switch terminal is connected to the wire running back into the environmental control unit. The third wire on the switch taps into the second black wire on the Sentra. Tape or shrink wrap job. Here is a wiring diagram:




Here is how it should look:




Now all that's left to do is find an appropriate place to mount the switch. Mark and drill through using a sharp drill bit. Mount the switch:



Looks good!

How to test:

With the engine running on a quiet street turn the fan knob to 1 and the cabin zone knob to defog. You should now be able to hear the A/C compressor turn on/off as you flip the switch.
 

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as a heads up, companies do this so the A/C compressor runs some in the winter months and doesn't lockup. I see why this is done however if you do it, it might be a good idea to kick it on from time to time so it can run a bit.
 

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Whoa, way too much work. All I did was unscrew the micro switch, flip it around, and screw it back in 180* from how it was.
 

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Its also done because when using ac to defog the windows it acts a a dehumidifier and makes it defog quicker
exactly...its air"conditioning". people dont relize that. they think the damn thing just blows cold...lol
 

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i just removed some of the wire insulation and twisted and soldered togther. works good... i had the HVAC control board out to do lighting mod so it was easy as pie...
 

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All I do is key off and then pop the clutch lol...works like a charm.
 

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hmmm...this is a nice find. I might like to add a switch, and use the ac to help defog ONLY when i want it done super quick.

First I have to see where I want to put the switch.
 

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you could just flip the microswitch and screw it back into the same hole so it doesnt activate with the dial, no splicing, no drilling, no worthless hassle and is completely reversible. this way when you want it to defog fast, you simply press the ac button. and waalaaa
 

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you could just flip the microswitch and screw it back into the same hole so it doesnt activate with the dial, no splicing, no drilling, no worthless hassle and is completely reversible. this way when you want it to defog fast, you simply press the ac button. and waalaaa
ahh yes. this is win, lol.

I will have to open it up and look at it. the "microswitch" should be obvious to spot, yes?
 

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the microswitch is on the underside of the hvac unit, it's on the knob that selects area (face, legs, defrost) if you flip the hvac unit over and turn the dial, you will see it hitting the microswitch when you put it on a setting with defrost. just flip the microswitch and screw it back in so the dial doesnt hit it, you dont need to take out the hvac unit, but it does have a cable attached to it, so its a little difficult to flip over. when you want the ac to come on, you press the ac button for moisture control.

edit: microswitch looks like mini black box with a metal type lever with 2 wires going to it and one screw holding it to the bottom of the hvac, you will see it once you flip the hvac unit over.
 

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the microswitch is on the underside of the hvac unit, it's on the knob that selects area (face, legs, defrost) if you flip the hvac unit over and turn the dial, you will see it hitting the microswitch when you put it on a setting with defrost. just flip the microswitch and screw it back in so the dial doesnt hit it, you dont need to take out the hvac unit, but it does have a cable attached to it, so its a little difficult to flip over. when you want the ac to come on, you press the ac button for moisture control.

edit: microswitch looks like mini black box with a metal type lever with 2 wires going to it and one screw holding it to the bottom of the hvac, you will see it once you flip the hvac unit over.
So doing this will prevent the ac compressor from running when the ac is not in use correct? I.e. heat on floor=no ac compressor?
 

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So doing this will prevent the ac compressor from running when the ac is not in use correct? I.e. heat on floor=no ac compressor?
this prevents the ac compressor from running when the "ac button" is not pressed, after you do this mod, the ac compressor will only run when you press the ac button, not when you select a defrost setting.

the microswitch automatically turns the ac on when you select a defrost setting and have the blower on 1-4. either defrost or feet/defrost or inbetween.
 

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this prevents the ac compressor from running when the "ac button" is not pressed, after you do this mod, the ac compressor will only run when you press the ac button, not when you select a defrost setting.

the microswitch automatically turns the ac on when you select a defrost setting and have the blower on 1-4. either defrost or feet/defrost or inbetween.
And the ac will be on and stay on without indicating so, until the car is shut off and started again with the position selector not in a defrost position.


Sent from my iPhone using Tapatalk
 

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i have an 02, i hear the 04+ ac has different cycles. normally i could select a non-defrost position and the ac kicks off upon selection, no need to restart motor here. maybe the ac stays off once it finishes its cycle?
 
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