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

SpicyorangeMSP

Registered User
Contributor
:
MSM MS3 CX7 626
Clearly the original poster is of an engineering background, a well thought up work around. However out of curiousity, of those of you who have done this how has it held up long term? I'm sure the AC still works, basically the "acceptable range" for the compressor to engage after voltage drop, and understand that completely. So the AC light won't flicker anymore. In the engineering realm i understand what this does and why it works.

However the root cause that i've found real world (which doesn't always mesh with the engineering world) is that the contacts inside the fan switch are very thin, and the surface area of the contact point itself leaves a bit to be desired. When clean, everything works great. However over time dirt accumulates in there, which adds resistance to the circuit. This added resistance inside the fan switch itself is why the voltage drops as much as it does, to put the "AC Sense" circuit out of range, and turning off the compressor (AC light turns off). resistance adds heat, and enough resistance/heat melts connectors and wires. Normally, if the AC quits working, you'll stop and choose a different fan speed that DOES work. You don't LEAVE it on the setting that doesn't work (and if you do, you've likely got damaged/melted wires/connectors behind the fan switch).

While this work-around does increase the operating range of the AC sense circuit, and the AC doesn't cut out anymore, you're not fixing the increased resistance through the switch itself, which in many cases melts connectors/wires/etc at the back of the fan switch. So i'm curious to some of you who have done this, hows it work out long term? Any signs of melting parts because you're basically ignoring that it normally "wouldn't" work and forcing it to work anyway.
I did mine on 6-29-14 and still working fine!
 

pcb

The Diagram Dude
:
2002 MP5
... Any signs of melting parts because you're basically ignoring that it normally "wouldn't" work and forcing it to work anyway.
My fix is working awesome.. I reduced the current through my switch to 20 milliamps using relays...

No heat... No meltiness.

 
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02 Protege LX, 03 P5 (x2), 09 Miata, 07 Mazda3, 13 Fit, 09 Ody
While this work-around does increase the operating range of the AC sense circuit, and the AC doesn't cut out anymore, you're not fixing the increased resistance through the switch itself, which in many cases melts connectors/wires/etc at the back of the fan switch. So i'm curious to some of you who have done this, hows it work out long term? Any signs of melting parts because you're basically ignoring that it normally "wouldn't" work and forcing it to work anyway.
Over a year on two different cars. No problems.
 
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2002 Mazda Proteg5
To CheeseHelmet I'd like to give you a massive thanks for this solution and write-up. This problem has been driving me nuts since I've owned both my P5s, and just this week I finally implemented this fix. So far so good! I have the highest hopes that this will finally allow the wife and me to keep the interior cool during the Phoenix summer, especially with the two little ones. Thanks again!
dusterbd13, I'd highly recommend attempting this fix if you are having this issue. For both my P5s it took me no more than a couple hours to get everything soldered and spliced, now both cars so far have flawlessly functioning A/C on all fan speeds!
I think I would be interested in making a few more of these and selling them, if anyone is interested please PM me.
 
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mazda protege5
I just did this and ac in speeds 2,3,and 4 are working now but 1 no longer works. Nothing works in 1, the fan doesnt even turn on but it was working before I did this.
 
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mazda protege5
Fixed it. I spliced into the wrong blue/yellow wire. But to be honest the directions should've been more clear. To clear things up for people that'll do this in the future, there are 2 blue/yellow wires in the vicinity. The 1 that you immediately see after removing the stereo is coming from the white plug(fan switch). This is not the right one. You have to splice into the blue/yellow wire coming from the black plug that is under the white plug. lol
 
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02 Mazda P5
Just did this now and wow 2 & 3 work now. Thanks for the how-to, but I did notice when on the off position the ac light stay lite and I can here the compressor still on is this normal. I know I can just turn the ac switch off, I did do all the step right
 

pcb

The Diagram Dude
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2002 MP5
Remember,...
You can always make your own fan switch...

 
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2003.5 Mazdaspeed Protege
I finally did this on my P5 last weekend. It worked absolutley perfect! All 4 speeds work great now and no light flickering of any kind. I hope it lasts.
 
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Mazda Protege5
Just wanted to come here and bump to say that this works for me!

Last summer (2017), I found a different write-up that suggested soldering the wires from the harness directly to the terminals on the blower switch. I did this, and it seemed to sort-of fix the issue. My a/c light would flicker moving from 1-2 and 2-3, but it would stay on for the most part. A couple of weeks ago, my blower switch died. I could not get the fans to even come on in any position. I ordered a new switch, grabbed a factory blower switch plug from a junkyard, and wired it up / installed the new blower switch. The fans worked, but the A/C light wouldn't stay on!

I completed this repair last night with wiring the resistors inline to the A/C detection circuit. Works like a charm. I'm really glad this was posted here - 100+ degree summers aren't fun without A/C.
 
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'02 Protege5
I bought a used P5 and the A/C only works only on fanspeed 1 but all fanspeeds do in fact function quite audibly I'll say. I'd like my A/C to function on 2,3 and 4. I followed this thread but before I start spending any money I decided to take a look myself. Then I followed a video on youtube to find the Blower Motor Resistor...

Video stated the Blower Motor Resistor was behind the glovebox, so I took a look https://imgur.com/uRk5ria Boy is that dirty! Took a deeper look https://imgur.com/q2QLA3x Holy shit! Looks like the Crypt Keeper sleeps in there!
So I reassembled it, started the car and turned to A/C on and to fanspeed 1 (fanspeed 1 always works) Still works so I put it on 2.. It worked! then I switched to 3 and the A/C light went off after about 10 seconds BUT the cold air was alot colder this time. I noticed that jiggling the board around by hand the A/C light would flash, stay on or strobe depending on where I hold the board. Awesome. I think I just need to clean something and maybe replace that resistor board. Can anyone comment? I'm just guessing here. I have no idea what I'm doing.
How do I clean that area behind the resistor board? Vacuum cleaner? What do people normally clean that area behind the board? If I disconnect the resistor board its self and clean the dirt off will my A/C on 2,3 and 4 work again?
 

pcb

The Diagram Dude
:
2002 MP5
Doing the resistor mod would most likely fix your flickering.
The sense wire on your car is right at the limit and keeps cutting out and flickering.
The resistor mod changes the settings on the sense wire to keep the AC and the light on.
The parts for the mod are just a few bucks.

Cleaning out behind the resistor is a good idea. Air will flow better. A vacuum should work.
 
Is anybody in the Philadelphia area interested in performing this fix on my 2003 Protege for $200??

My wife has had enough of the AC only working intermittently and I'm going to have to move on from my beloved Mazda if I cannot get it fixed. I was able to pull out the radio and start poking around, but I'm really not sure what I'm doing so I didn't get much further than that.

Please let me know if interested!!
 
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