A/C purple wire mod with a twist

[jlkuehl]

I know the ”purple wire mod ” has been discussed, hashed over, complained about, and showed off until everyone is sick of it, but I have to add my version of it in. I simply can't do anything as easy as putting splicing in a switch and calling it good. First off, during the winter my gas mileage drops from between 28 to 30, to 25 or so. With only having the 2.3 under the hood of my 06 XLT and driving roughly 300 to 400 miles a week, I've noticed that I can feel the power loss when the compressor kicks on. I know some of the loss is due to winter blended fuel, but I can't ignore the feel of the compressor cycling.

So:

1: the compressor cycles to circulate oil and keep the seals good
2: it also cycles to dry the air in the cab and speed defogging.
3: I'm a forgetful idiot, and would most likely wind up turning the compressor off, and not
letting it cycle from time to time.
So, my solution to all three issues is this

I wired up a relay into the purple wire so that the compressor signal wire would operate normally when the truck is first started. After the truck is warmed up and the windows are defogged, I can press a momentary switch, which activates the relay, which is wired up to hold itself in the switched position. Once the button is pushed and the relay activated, a red LED is turned on, and the purple wire is open.

The system is reset to normal function when there is no voltage present at the purple wire, such as the blend door selector knob is turned to off or vent, or the ignition is turned off.

The entire system is contained under the shifter console (manual transmission), with all wire and relay hidden. The push button and LED are on the driver's side of the console, in front of the cup holders.

I don't think this mod alone will bring my gas mileage up to summer numbers, but I do anticipate a bit of a gain, maybe from 25 back up to 26 or 27.


This is the circuit I used. The resistor labeled powertrain ecm is only there to show where the purple wire runs to (without it, my circuit design software showed short to ground), and is not added into to actual circuit. The resistor for the LED should be around 270 ohms, 1 watt rated for the average automotive system.

It's also important to note that power flows from the red connector on the climate control panel to the pcm. This would put the red connector before the momentary switch, and the pcm end of the wire connected to the normally closed pin on the relay.

 

[alwaysFlOoReD]

Hey, thanks for posting. I've never heard of the purple wire mod, so this is new to me.

Richard

 

[jlkuehl]

From what I can tell, most people cut the purple wire going to the red connector on the back of the climate control panel and splice in a switch. Since this wire tells the pcm to cycle the compressor or not, it's a simple mod to trick the pcm into thinking the position selector is either off or in vent position. I'm just too forgetful to let the compressor cycle a bit, so I needed a different solution.

It's been a long time since I posted last, I figured this might be something others would want to see, though. I cobbled it all together using parts I had sitting around, so there was no cost involved. If I had to buy the relay, switch, led, and resistor, it would still cost less than $10. Best kind of mod, free or cheap'r than dirt.