The dreaded A/C Issue!

[crazywhitte]

Alrighty folks, I know it has been discussed and a solution has been provided for the A/C not coming on when you turn the fan speed up.. I have completed the solution and even soldered all the wiring to ensure a great connection and it didn't fix my issue. Before I had my radio out and would move around the wires connected to the fan speed switch and it would kick the a/c. I would still have to constantly mess with it to ensure it stayed on when I had the speed greater than 1 (The A.C. works perfect on 1 even after the resonator fix). Anyone else have this usse and it not be fixed? What's my next step? Thanks Y'all!

 

[pcb]

A new fan switch may fix your problem.
They get all burnt up inside.

Cleaning up the connectors on the fan switch can help, and soldering them on is even better.

 

[crazywhitte]

Soo my car had a brand new one in it when I bought it. And I've pulled two out of the junk yard and none of those have fixed it either .

 

[pcb]

You may have to do a few things to get it to work.
The resistor fix, a new fan switch, a new resistor pack, and a new wire harness from the fan switch to the resistor pack.

The key is to reduce the resistance from the fan switch to the resistor pack to the blower motor so that the sense circuit doesn't kick in.

A used fan switch will most likely have the same problems.
I don't think there are any P5 owners who haven't had to deal with this problem.

 

[INYOURCHAIR]

did it lol. I followed another guide that involved actually opening the climate control to get at the circuit. involved pulling one leg of a diode, and soldering a couple resistors in there. I dug in the thread I posted abut it and found I used a 470ohm and 200 ohm as a substitute for a 1k and 2k. it worked with the lower resistance on the second try. I paid usd $9 for a multi value 1/4 watt resistor pack. but you could order the two values in a 10 pack. The soldering isn't on the easy level though. Mine has worked flawlessly since. I am keeping an eye on my fan switch though lol. If I were to restomod this car a complete wiring harness overhaul would be needed. that fan wire gets HOTT on full blast.

GF's P5's AC was working intermittently. Cleaning the fan switch temporarily "fixed" the issue and further research and perusing the AC system schematic shed light on Mazda's mickey mouse attempt to make sure that fan was on before engaging AC compressor. They sense the voltage drop across one wire to enable the compressor. Problem is that if there is no significant voltage drop between the sense point and +12V then it doesn't trigger the circuit. It wants to see lower than +12V.

One of the several fixes I've see require making a voltage divider using resistors and inserting into the wiring harness.

Cutting or otherwise mutilating a car's electrical wiring is one thing that I completely hate to do; they are problematic enough as they come out of the box without any molesting, I decided to do the mod on the PC board itself.

I bought a used AC control panel and removed the PC board, kinda fiddly but doable if careful enough.

Looking in the AC wiring diagram I see that the sensing signal is supplied to the PC board and the sensing circuit through diode D5.

I used a different value of resistors than the"fix" because I wanted to reduce current draw while using 1/4W resistors. -as long as the resultant voltage is between 4 and 6 Volts, it works.

I lifted D5 from the board, placed a 2K Ohm resistor from the cathode trace of the board to the cathode of D5. Then used a 1K Ohm 1/4 W resistor from the ground pin on the connector [third from right, top row] to the junction of the 2K resistor and D5.

As a further precaution I replaced the fan switch with a new OEM part. The old one had excessive resistance between positions which further offset Mazda's [poorly] designed sensing circuit.

First picture; D5 location
Second picture; D5 removed
Third picture; completed mod. Fuzz is from Q-tip used to clean flux from board.

View attachment 229127View attachment 229128View attachment 229129

 

[BenjiHoggi]

Yay thanks for revisiting this dreaded topic. It's been driving me crazy. I've tried unsuccessfully to fix it multiple times. Tried the resistor fix a few times but no luck.

did it lol. I followed another guide that involved actually opening the climate control to get at the circuit. involved pulling one leg of a diode, and soldering a couple resistors in there. I dug in the thread I posted abut it and found I used a 470ohm and 200 ohm as a substitute for a 1k and 2k. it worked with the lower resistance on the second try. I paid usd $9 for a multi value 1/4 watt resistor pack. but you could order the two values in a 10 pack. The soldering isn't on the easy level though. Mine has worked flawlessly since. I am keeping an eye on my fan switch though lol. If I were to restomod this car a complete wiring harness overhaul would be needed. that fan wire gets HOTT on full blast.

I will look into this more. I have boxes of electronics for hobby stuff and I love soldering, so the more the merrier!

I don't think there are any P5 owners who haven't had to deal with this problem.

My brother's 2003 ES Sedan with 186k doesn't have the issue. You bet I checked when he bought it. I asked the seller and he knew nothing of it being serviced.

 

[BenjiHoggi]

I did the repair you linked INYOURCHAIR and it worked! I have working AC now for the first time since I bought the car. So hyped now, that's been a sore spot with this car for a long time.