Noise when recirculate button on - Ideas? Youtube Vid

[Yukkman]

This just started yesterday. I changed he cabin air filters. No idea what it would be.

Noise only happens when the recirculate button is pressed (on) and fan is on.

 

[wjburken]

This just started yesterday. I changed he cabin air filters. No idea what it would be.

Noise only happens when the recirculate button is pressed (on) and fan is on.

It is tied to engine speed it sounds like so my first guess would be a bad compressor but see if you can pin point where the sound is coming from.

@UmmScott might have more insight on this.

 

[UmmScott]

Wow man that is very weird indeed.

Gotta pinpoint what is causing the noise. Sounds like its the compressor clutch or compressor itself?

This actually might be the control head itself. Recirc should in no way affect compressor clutch operation other than forcing AC on.

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[UmmScott]

Heres a test you need to do if you do in fact determine that the noise is coming from the compressor and/or clutch..

Backprobe into the electrical connector right at the comp clutch and take a voltage reading. With the AC on you should have normal steady 12-14 volts.

If when you turn the recirc on the voltage changes or becomes erratic, Then something electronically is failing and in that case i would suspect the control head for sure. Maybe for some reason when recirc is on the head is having issues internally and is causing the ECM to erratically cycle the clutch.

I wish i knew what the clutch Ohms are supposed to be but...if it only happens in recirc mode, then i dont think the clutch is the issue.

This is gonna be control head, AC clutch relay, ECM, or a ground issue.
I highly suggest try swapping the AC clutch relay first. Its free and takes 30 seconds and then go from there

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[Yukkman]

Thanks guys for the quick replies. Luckily the super hot weather in the bay area Cali is gone and I don't need to run the AC on recirc for a while.

It's an odd noise as the function of the recirc is just to open and close a door right?

 

[UmmScott]

Exactly..

Recirc just opens/closes the recirc door. Nothing else.
Only other thing it will do is force the AC to come on as well in some circumstances.
Other than that it shouldn't affect any operation under the hood

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[OR VietVet]

Does sound like a rattling a/c clutch or compressor problem but when just the recirc is on makes it strange. Are you sure there are no other HVAC controls switched on that you are not aware of?

 

[rockola1971]

I wish i knew what the clutch Ohms are supposed to be but...

Power equals E x I (Voltage times current) I would expect to see power to be 60w to 90w. So manipulate the formula we will. (Yoda says so)

60w divide by 13.8v equals 4.347A. Resistance equals E(voltage) divided by I (current). 13.8 divide by 4.347 equals 3.17 ohms.

90w divide by 13.8 equals 6.521A. Resistance equals E divide by I. 13.8 divide by 6.521 equals 2.11 ohms

I could be off and the actual wattage (slightly higher or lower) So I would expect to see 1ohm to 4ohms resistance on the electromagnet on the clutch. Take at look at the fuse rating for the clutch and you will get a slightly better idea of the current draw. Actual draw should be 80% or less than the fuse rating.

Usually when the clutch itself fails (electrically) you will see on of two failures. (1) the coil burns open and no longer conducts a complete path. (2) the coil melts together(Internal short) which lowers resistance and this causes power to go up and the wire in the coil is not rated for that high of power and the heat created melts what is left even further together until ultimately the fuse blows because current draw exceeds fuse rating. These are INTERNAL electrical failures, not to be confused with external power feed failures such as the connector, wiring harness to the clutch, etc.

Noise sounds in the video sounds like the clutch magnet is making chatter noise. Check wiring harness plug at clutch for corrosion or loose connection. Could also just be the electromagnet of the clutch is failing to hold the pulley to engage the compressor input shaft. Unplug the compressor and push recirc button and see if the noise is gone.

 

[Yukkman]

Does sound like a rattling a/c clutch or compressor problem but when just the recirc is on makes it strange. Are you sure there are no other HVAC controls switched on that you are not aware of?

The fan is on and recirc BUT when recirc is off the noise goes away. I'll check it out again tomorrow and see.