AC Interior Noise: Varies with Speed

[cebra]

I have read through threads on blend doors, actuators etc but I couldn't find what my truck is doing. I have a fairly loud interior noise from PS foot well area when I turn my AC on. It varies with rpm (not speed). It is a kind of rattling, brrrt, noise like a wheel bearing when it starts going out but definitely coming from inside or around the hvac box under the dash. What part would this be, doesn't sound like a blend door from what I have read? I may need to check to make sure the AC blows cold on the PS side though to be sure.

[EVRLET]

Sounds like the blower motor. Blend door actuators click. It’s a plastic clicking since the gears are plastic. You can put your hand on the lower passenger side blend door actuator when it clicks and feel it.

Turn off the HVAC and does the sound go away?

[cebra]

It does go away with AC off. It is loud at idle, then has a reverberating type noise (maybe a clicking but it would be clicking really dang fast) that varies with engine rpm. At highway rpm it is barely audible.

[EVRLET]

Since the blower motor operates for both heat and AC, have you tried turning the system on in the heat only mode? Does it go away? Those motors do not fluctuate with engine RPM.

You can remove the motor, hold it in your hand tightly, turn it on and know for sure if it’s the motor or not. Or grab a hose and place one end on the outer motor housing and the other end on your ear. Turn it on and see if you can say yep, the motor.

I can’t think of anything in the interior compartment that fluctuates with engine rpm. Maybe electrical noise through a poorly grounded stereo, but that’s it.

[cebra]

Thanks, I'll try but it doesn't make any noise in heat, cool (without AC on etc). When I click the "AC" button it starts and when I click it off it stops, I can do this on and off driving down the road....AC on, noise on, AC off, noise stops. I'll try to diagnose it better with someone else revving the motor, thought it may be a common issue so wanted to ask first to get me in the right direction. I am pretty sure though it is coming from inside the HVAC "box" under the dash on the PS so I at least got it somewhat narrowed down. Just need to figure out what all is in there, actuators, motors, etc.

[EVRLET]

Keep us posted on what you find