dougm213

Anyone experience a 2 second motor noise sounding like something controlling the air handler flaps at cold startup? Started when cooler weather arrived. Happens every 15 seconds for a minute or 2. This morning only once. Reminds me a the fuel pumps on the older Airbus 320 after landing moving fuel from one wing to the other. I can not recall it happening in other years/

bclexus

My guess is that the motor noise you're hearing is coming from the air mix (blend) damper servo motor unit. This air mix servo motor unit has a small motor that gets its input signal (voltage) from the vehicle's HVAC system to either open or close a damper door that controls the flow of blended air through the dashboard ducts. Usually an amplifier circuit in the HVAC system controls this servo motor, and uses positive or negative voltage to the little motor to move the pivot arm (forward or reverse) that opens or closes the damper door...based on cabin air parameters, e.g. temperature, humidity, etc.

These servo units are rather delicate and can easily become damaged when one or more of the multiple plastic reducer gears (worm and spur gears) become unmeshed or broken, or the unit's plastic pivot arm that opens/closes the damper door becomes jambed. Most of the time the culprit is the little worm gear that is mounted on the tiny motor's shaft breaks. This problem exists in different car brands and models, not just Lexus/Toyota.

Some DIY owners (with cars that are out-of-warranty) have elected to try to repair/fix the damaged servo unit - some successfully, and some not. I think the price of a new servo unit is around $150 to $200. I've heard that some labor (only) estimates have been as high as $800 to replace a defective unit. I feel sure that some models are a lot more labor intensive to replace than others.

Typically, you will hear the clicking/grinding noise from a defective servo motor unit when the temperature is colder or warmer than your vehicle's system is set...and when the vehicle's inside temperature comes close to matching the desired temperature (or when the outside temperature matches the desired set point temperature) it will start making the noise - in other words for example, the car's HVAC temperature is set on [say] 72° and the car's inside temperature is (or has become) ~72° and the outside ambient temperature is about the same at ~72° - this is when it reaches the (thermostat) threshold and the servo motor receives its signal voltage to operate the damper door....but there is resistance from something (gears are locked-up, etc.) so you get a whirling, clicking or grinding sound.

The air mix servo motor unit is located behind the dashboard near the center, beside the duct work that feeds air to the supply outlets.

This is what a typical air mix servo motor unit looks like...

Tcagle

Wow great explanation! Now about that DIY thread.....

dougm213

Thanks for the great information.

I was thinking it would be something like this. My car is still under warranty and am taking it in for inspection and a check engine light tomorrow, so I will add this to the list of things for the dealer.

Shinedown

Now that it is getting colder here in Ma my 2013 GS has been exhibiting the same noise at startup. When I start my car there is a motor noise that eminates from the dash, this almost sounds like a cd ejecting, and it has a brief pause between noises. This noise will continue until my car warms up. My car is under warranty so I'm thankfully not concerned with cost, but the idea of taking my dash apart is a bit scary. Bclexus is this a difficult job for a Lexus tech to perform and get right? I expected this from my '99 BMW 540i but not my Lexus GS

Dallasguy1

some sound started coming after replacing the cabin filter, booked an appointment but it went off after driving couple of days. If the sound is persistent then yes could be the blower motor.

bclexus

I do not know how difficult it is to get to the servo motor units in the GS 350, so I cannot answer your question. But in all likelihood I would guess it will be difficult. And, like doctors and car washes, some technicians are better than others...