Knocking Sound when the A/C or defroster is on...

[Chriscoe]

1998 4Runner 3.4L SR5 4X4
Every time i cut my air on with the A/C turned on there is some sort of knocking sound coming from the passenger side under the hood. This sound also occurs when the my knob is turned to defroster. It sounds as if something is turning on and off because if you stick your head under the hood and listen something sounds like its engaging and then the noise starts.

Any help from you guys would be awesome.

 

[Dous]

1998 4Runner 3.4L SR5 4X4
Every time i cut my hair on with the A/C turned on

Hmmm I will have to try that next time. Usually I cut my hair with the heat on.

 

[Chriscoe]

Hmmm I will have to try that next time. Usually I cut my hair with the heat on.

Yeah man you should try it.

 

[Dous]

Seriously though, could be your compressor going out. What you hear turning on and off is the compressor, it has a clutch, and when it engages you will hear a single click.

I would get a mechanics stethoscope and put it next to the compressor and I am sure that will be the source of the noise

 

[Chriscoe]

So probably need to replace the entire thing?

 

[Chriscoe]

Bump

 

[Chriscoe]

Bump