Does anyone recognize this deafening sound? It's driving me crazy.

• It's intermittent and will sound for a few seconds at a time
• Sound has been heard with A/C on and off, so I don't think it's the A/C compressor.
• Sound returns more frequently with A/C on. Sometimes the sounds will immediately subside when I turn the A/C off. Maybe one of the fans?
• Seems like its is coming from the driver's (LH) side of the engine bay
• I can feel a small vibration under my feet when the sound returns

If I had to guess I think it has something to do with one of the electric fans, but I'm just not sure what exactly.

 

It could be that the A/C clutch is worn out and is partially engaged, or like mine where it wore out so much that the clutch pulley separated in two, locked itself to the engine block and then the secondary belt squealed/skidded/grinded over the semi stationary pulley after that.

Alternatively, I don't know where US Evo 9's keep their ACD pumps - do you have one in the front left of your engine bay? Maybe something is failing there. Find your ACD ECU, completely disconnect it and then run the car. Is the sound gone then? It is mechanically/electronically safe to drive the car with the ACD system turned off.

 

I re-shimmed the A/C clutch and it spec'd out. The fact that I have heard the sound with the A/C off AND that the A/C works great leads me to believe that it isn't the A/C compressor.

ACD pumps are in front of the left front wheel on US Evo 9's. Good call on disabling the ACD as a test, I may just try that..

 

could be the fan. careful there, I have bought a bracket with a burnt fan (like electric fire burnt)

 

Just wanted to update this thread with the fix for anyone else experiencing this issue. It was the AC fan! The fan appeared to have rounded off the flat spot where it mates with the motor shaft, which is strange since the nut holding it on was still tight. Maybe it came loose at some point did some damage and the nut was retightened.

Anyhow, the entire AC fan was replaced with an aftermarket from RockAuto (OEM is discontinued) and the sound hasn't returned.

 

which fan was it?

 

AC fan lol the smaller one in front of the condenser and right behind the intercooler.

 

I think both fans are AC (right side) & radiator (left side) fans

 

well I think the front fan is the one that turns on and off constantly when the AC is on so its the primary AC fan? It also turns on when the AC is off so I guess its also an auxiliary radiator fan 🤷

 

mine turns on at the same time. front fan is mostly in low speed mode without AC on

 

Yeah functionally it also serves as a front radiator fan, but Mitsu and every website I've seen labels it as an condenser fan.