My friends Yukon XL is making some strange whining sound when the A/c is on. He said its coming from behind the dash. Its an 02 Yukon XL. Any suggestions as to what it is and the fix?

 

Possibly the blower motor or a blend door stuck half way open? Does the noise increase with the blower fan speed? You could also try different air flow settings and see if the noise changes to try and narrow it down.

 

Orifice tube........

 

Whats that?

 

converts the system from low pressure to high pressure

 

Isn't the orifice tube located out front by the condenser?

 

Im pretty sure my silverado does the same thing but it makes a loud noise like its letting of steam, from the passenger side towards the front of the truck

 

Negative. Its right up by the firewall going into the dryer!

Orifice tube "hiss" really is normal.