Cannot Change The Direction Of Airflow From Vents

hillom14 · April 4, 2012

A few months ago, my 99' RX300 stopped switching the flow of air from anywhere but the vents. Even when I push the button to switch to front defrost, floor, floor/vent, defrost/floor, etc, the air continues to only blow from the vents. The adjustable fan speed works fine, as well as the heat and A/C, but it does not respond to changing the direction on the dash. Even when put on floors only, the vents continue blowing. Also, and i'm not sure if this is directly related, but just recently another problem has arisen. Upon turning the key to on (with the engine still off), an electric motor behind the glove box begins to hum louder and louder for approx. 5-10 secs, then stops abruptly.

I've read a few forums about problems with air servos that would probably explain the humming i've been hearing, but I was curious as to if a failed servo would account for the inability of my car to recognize a change in airflow direction?

Anyone have an ideas?

Filehorse · April 5, 2012

The most likely culprit is the Mode Servo which is the one that changes airflow from defrost to vents to floor. If you plan to keep the vehicle, I'd suggest you replace both the Mode Servo and the Air Mix Servo (controls temperature) while you're in the area. Both these servos are available online for a lot less than your local Lexus dealer will likely quote you. It's also a fairly easy DIY if you don't mind standing on your head under the glove box for about an hour - maybe less. There are lots of writeups and pictures available covering this procedure. I replaced both of my servos last year. The trickiest part is removing one screw that will probably be at least partly obscured by one of the aluminum tubes routing hot water to/from the heater core. You can carefully pry the tube to one side enough to remove the screw without any real difficulty. This is also a good reason to be sure the engine is COLD before you start this process. If you follow someone's writeup and you have the requisite stubby #2 Phillips screwdriver, you should expect to go start to finish in a couple of hours or less if you've never done this job before.

Also, if you are actually going to go to the trouble to remove these servos, go ahead and REPLACE them. You can take them apart and clean the contact surfaces but this will most assuredly be a short-term fix and you'll be right back in there to replace the servos when the problem resurfaces in short order. The problem is less a one of dust/contamination than it is of a wearing of the internal "painted" contact strips.

The following link provides a LOT of information/pics on the How To for this little job. http://www.clublexus.com/forums/esp_search.php?query=air+mix+servo&ref=esp-nav-bar&type=all

I bought my servos from Stevinson Lexus of Frederick, CO. http://www.partswebs...=108&type=parts

You might shop around the Internet and save a few bucks but these prices are very competitive. I gave my dealer the opportunity to meet the price but he couldn't/wouldn't come close.

Lotsa luck.