How-to: Permanently fix the "no A/C on fan speed 2/3" problem

If your A/C light is flickering (or doesn't even come on) on fan speeds 2 and/or 3 this is a simple solution that will hopefully fix it permanently. The original solution posted many years ago never really addressed the root cause of the problem. Almost 3 years later pasadena_commut came up with a solution which would definitely fix the problem, but I always thought it was much too complicated. The method I describe below is simple, cheap, and can be put together and installed in less than 30 minutes.

This is just a mirror of a how-to I posted here. If you'd like to know exactly why this problem occurs and how the solution works, click here.


Materials

The only thing you really need to do this are two resistors that are close to 470 Ohms (yellow-violet-brown) and 200 Ohms (red-black-brown). I'll list everything I used just for the sake of completeness.

Materials:
  • 1x 470 Ohm resistor (1/4W or greater)
  • 1x 200 Ohm resistor (1/4W or greater)
  • 2x Small/Red crimp-type butt connectors
  • 1x Small/Red solderless quick splice connector
  • 3x 20cm length of hook-up wire
  • 1x 10cm length of 1/4" heat-shrink tubing

Tools:
  • Soldering Iron
  • Wire cutters/strippers
  • Crimp tool
  • Small flat-head screwdriver
  • Radio removal tool (made from a coat hanger)


Instructions

These instructions are merely the process I used, feel free to get creative.

Prepare the resistors



Attach wires, solder, and trim

This is the colour code I used for my wires:
  • Black - Ground
  • White - Input
  • White/Blue - Output



Add some heat-shrink to isolate everything

Tape works just as well...



I pre-crimped and labelled my connectors to make sure I don't mess up




A quick primer on how to remove a stock Protege radio

Remove the plastic covers on either side of the radio.


Insert two bent pieces of coat hanger wire into the holes as shown. You'll feel them lock in place when you get far enough (don't be afraid to force them in there). Push your tools towards the doors while pulling out and the radio should just slide out. You might not get it the first time, but when you do you'll be able to steal a stock radio in less than 15 seconds ;)

Remember to remove the antenna and main radio harness connectors before proceeding.




This is the wire you're going to cut (Blue/Yellow)

It's much easier if you remove the connector from the back of the climate control unit to give yourself more room to work.



Cut and strip the wire

Try to cut away from the connector ... just in case you make a mistake.



Connect the circuit you made previously
  • Connect the "output" to the wire that's still attached to the connector (the right butt connector).
  • Connect the "input" to the wire that's buried in the harness (the left butt connector).



Connect your ground

Not very surprisingly, the black wire in that harness is ground. Splice into it or use any other bare metal to make your ground connection. I used one of those fancy solderless quick splice connector's just because I had some handy.



Enjoy some A/C at a proper fan speed

Seriously, 3 is the best speed.
 
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:
Mazda Protege5
i did it with no hiccups!
and if I can do it, then a brain dead monkey can do it.... not too sure where to get a monkey.... but you know what i mean

(btw, 2 is the best speed)
 
i did it with no hiccups!
and if I can do it, then a brain dead monkey can do it.... not too sure where to get a monkey.... but you know what i mean

(btw, 2 is the best speed)
4 is the best...
^You people don't know what you're talking about, 3 is the best :p

Yup, that's a simpler circuit than mine. Good job.
It would be even simpler (and probably more robust) if you changed that one bias resistor on the PCB to a lower value, but I didn't think people would want to do that... Oh and sorry, I forgot link to your solution (fixed now).
 

zhy

:
I aint even mad!
This calls for a sticky really.
fan speed preference hahaha. really good work nick, cant wait to meet you tomorrow.
 

THE Phen

Phenda Bear
:
2013 Abarth, 2004 MSM - FM, '74 BMW Bavaria, 97 Civic EX B18C1
There was another write-up done on this a few years ago, but this is definitely a bit better. Nice work.
 

Hank3

Asian Persuasion <><
Contributor
:
2010 Mazda5 GT
Great job, CheeseHelmet. I never really had the gumption to attempt any of the other fixes for this, but you've made it easy enough where it's now on my radar to do. Even then, I'll probably wait till the Fall to do it. This way the fan will be ready for next Summer! :)
 
:
Protege5 2003
I used one of those fancy solderless quick splice connector's just because I had some handy.
Some folks claim that these sorts of connectors are not a good idea for cars. They think that the constant vibration of normal driving causes wear at the wire/metal contact, which can eventually result in the contact failing, or even the tapped wire being cut (worn through). I don't know if this is a real worry or not, but just to be safe I soldered and shrink wrapped all the connections on my fix.
 
:
02 Mazda Protege5
This is awesome...my fans just started to give me a headache. Added to my to-do list! Awesome write up too!
 
Some folks claim that these sorts of connectors are not a good idea for cars. They think that the constant vibration of normal driving causes wear at the wire/metal contact, which can eventually result in the contact failing, or even the tapped wire being cut (worn through). I don't know if this is a real worry or not, but just to be safe I soldered and shrink wrapped all the connections on my fix.
That's a very good point, I just used it because of the novelty of using one of those connectors. If I were doing it on someone else's car I'd crimp it or solder it properly.
 
:
2002 Protege5
Cool! I don't have my diagram handy. Remind me what this is doing? Is it just ensuring that the compressor sense wire sees ground in every ON position?
 
:
Mazda Protege5
Nice Job. I'm going to absolutely try it out this weekend.
Great write up, very simple and straight forward instructions. Good work.
 
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