Disable Air Conditioner-On in Defrost


All modern cars that I know of are designed to engage the Air Conditioning whenever the Defroster is turned on (this includes any settting that involves the defroster: "heater+defroster", etc.) The problem with this is you are placing wear-and-tear on the Air Conditioner without actually needing it. And there are those rainy, humid days when you have to run the defroster vertually non-stop - I just can't see wasting all that A/C for no good reason.

"So, how do you disable this function?"

Every car is different. If your Heater/Air Conditioner control is basically a mechanical-type switch, you just need to locate the A/C wire that's connected to the Defrost function. But most cars have these functions controlled by the main computer, which makes it a little more complicated.

1. For the computer-controlled Heater/Air Conditioner switches, you need to locate the lead that sends the Air Conditioner signal to the Main Computer. A wiring diagram will be necessary to determine this (e.g., from a Haynes manual), and then confirm the lead with a meter test.

2. The second stage is: you will have to splice a switch into this lead. Keep in mind that since there is no separate lead for the normal A/C and the defroster's A/C, this switch will turn the A/C on or off for ALL controls, including normal A/C. You'll just have to remember to turn this additional switch "on" whenever you select the regular A/C switch on your dashboard.

That's my experience, here are some other searches, links, and comments:



www.tundrasolutions.com/forums/interior-and-exterior/31448-wiper-question-wipers-suck-esp

[Toyota Tundra]: Take the face plate off the center of the dash and remove the wire from the air control knob assembly. That turns on the air conditioner everytime the air control is in the defrost or floor/defrost position. You'll have hotter defrost air. Any time you want the a/c on to de-fog, just push the a/c button.

Actually, I've disconnected the a/c from my defrost setting and I'd suggest that to everyone.

http://www.gweep.net/~sfoskett/miata/favmods/index.html

[Miata]: All you have to do is disconnect a single connector behind the vent selection knob. Once it is disconnected, the A/C and defrost operate completely manually: The hard part is reaching the connector! Once you can reach the connector, look at the connector with the red circle around it. PHOTO: www.gweep.net/~sfoskett/miata/favmods/Defrost%20AC%201.JPG

Push the lever at the front on the top and pull the connector off. Now fold the connector back and tape it to the wiring bundle behind it. You're done!

http://forums.nicoclub.com/zerothread/184367

[Nissan:] there is a small micro switch with about half a dozen small wires running to it. It is held in place from below by one tiny phillips-head screw about an inch long. You can see the tip of it on the top of the housing...

2. Remove the tiny screw from the bottom of the switch.

3. Move the switch to the top of the white housing, and screw it right back into the same hole from above...

http://www.dodgepowerclub.com/dodge_power_club_130.htm

[Dodge RAM site:] Remove the four screws holding the climate control to the dash. Turn the temperature control knob to the coldest position, push in on the red cable lock that holds the damper control cable in place, tip the cable up and remove the cable from the sliding gear. Pull off the temperature control and the mode selector knobs.

Disconnect the electrical plug and the vacuum distribution manifold from the rear of the unit.

Remove the unit and notice the black tamper-proof screw on the back of the unit. We filed the center of the screw down until the Torx size T10 driver could get a grip on the screw. Remove this screw, then use a screwdriver to pop the four plastic retainer tabs from the four corners of the rear of the unit and remove the rear cover. Take caution at this point, as we broke one of our tabs off.

See the BLACK WAFER that corresponds to the mode selector knob, take it out, notice the two contacts grouped together. Well, pry out the OUTER CONTACT and its spring. If you remove the inner contact, the fan will not work at all. Then reassemble the unit, reinstall it and put the dash back together. No more ac on defrost.
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For 1998-2001 Rams with the 4 position fan switch (computer controlled):

The fan switch does not have a position for AC, so a separate switch must be added to the HVAC control to disable the AC compressor. If the HVAC control is disassembled and the defrost contact is removed, the AC will be permanently disabled. The only option for a selectable AC disable switch is:

Cut the Light Green/White wire from the HVAC control
Wire a small switch into the circuit and mount the switch near the HVAC control.
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[Toyota: COMPUTER CONTROLLING the A/C function] The wiring diagram for my '02 shows a COMPUTER CONTROLLING A/C FUNCTIONS· I suppose it is possible to install a toggle switch in the power lead to the AC compressor clutch· No power = no compressor = no AC regardless of what the computer says to do· 
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[Lexus] Disable your A/C compressor ... Typically, you can simply disconnect the electrical connection to the A/C compressor clutch to do this.
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LINKS:

Information is lean on this subject, so several changes of keywords are necessary. Here's a start:

GOOGLE SEARCH 1: disconnected, A/C, defrost

GOOGLE SEARCH 2: disconnect, automatic, A/C, turn on, defroster, disable

GOOGLE SEARCH: disconnected, A/C, defrost, Dodge


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