Hvac Weezing On '02 Tahoe

[Stephenspann27]

I bought a 2002 Z71 Tahoe a week ago and this problem was pre existing. The HVAC system works flawlessly. However, on the passenger side, under the dash where the blend doors etc are. There is a loud weezing/wooshing noise with the fan is on, it is even louder when the system in on recirculate (probably because when recirculate is off, the intake door is closed and in insulating the noise a bit). The noise is not coming from the fan motor its self. The noise is the same regardless of what position the air is blowing (feet,defrost, etc.) Before I tear it apart, I was hoping you might guys might have some info on which door/flap I should inspect.

Thank you

[pz4m0m]

Having worked in the facility that made these HVAC units for all full size GM trucks I would like to help you out. My gut feeling is that something is caught up in the intake plenum of the A/C unit or you have an air leak whistle: if changing modes doesn't affect the noise, than I would look into other areas before going thru the pain of rolling the IP to get at the temp / mode mix doors are in the center of the IP, so if the noise is clearly coming from the pass side I would not go there. The evaoprator core sits just above the passenger's left foot, and since all air that goes thru the unit must go thru the evap core, debris cannot get past this point in the system.

 

Since you stated the noise is not coming from the motor itself, I assume it doesn't change with fan speed? Bad motors will typically "squeel" and the noise is usually morre prevalent at lower fan speeds. I have not heard of HVAC noises described as "weezing/whooshing" before... Does it change when travelling at highway speed under the natural "ram air" pressure that is created? If it is a "Whistle" that changes with air speed I would try and close in on the exact location of the noise, which may be coming from an air leak where the two halves of the upper and lower case halves come together. If it sounds like something is vibrating or flapping around in there, I would drop the blower assy and inspect for any debris which has been sucked into the intake plenum / is caught up in the recirc door. You should be able to drop a hush panel / go thru the glovebox to gain access to the blower motor. This door (along with the mode doors) are driven by small gear motor actuators, but you should be able to open and close using the recirc button as long as you are not in any defrost mode, which commands this door to outside air position for safety reasons. From the fan motor opening you should be able to see what is going on in there. It could also be coming from refrigerant flow inside the evap itself. As the compressor cycles on and off, it may yield a faint "hissing" type noise, which can be a sign of an undercharged A/C system: it may still have enough refrigerant in it to cool air and appear to perform OK in moderate load conditions like we see this time of year, but has leaked off enough charge to cause both gas and liquid refrigerant to be "spurting" into the evaporator inlet. If you can affect the noise by cycling the A/C on and off (beware of "auto" mode if you are so equipped which may be cycling the A/C on and off for you: you may want to watch the A/C compressor clutch to see if it is cycling on and off.) Hope this helps: please reply with (hopefully!) successful diagnosis or more info as to exactly what you are hearing, and anything you have found which changes to noise so I can try and help you resolve it.