AC light flicker -- FIXED

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.

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Ummmm.

Asking for a friend: Would you mind explaining it to me like I"m 5? My "friend's" P5 also have this flickering and is interested in trying this.
 
Ummmm.

Asking for a friend: Would you mind explaining it to me like I"m 5? My "friend's" P5 also have this flickering and is interested in trying this.
De soldering components and modifying PC boards is something that takes practice and finesse, not to mention the right tools.

For the average punter follow the instructions in this thread, have someone make you the voltage divider and insert it in the proper wire.
Order a new switch from Mazda and replace it as well.

Sorry if this is above your friend's skill level.
 
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