Thanks to the generous members of this site, I have learned that I most likely have a mode servo problem. Symptom is buzzing in the dash behind the climate control panel. The buzzing comes on intermittently and goes off when the mode switch is actuated. Vehicle is a 2001 RX300 with 125K miles. We have not noted any air flow issues yet.

If I understand the issue correctly, the mode servo design allows the worm gear to disengage from the driving tab on the motor shaft. The noise is most likely the driving tab clicking against the lip of the slot in the worm gear as the motor turns.

Having read many of the threads covering servo replacement or rehab, my questions are these:

Is it worth trying to rehab the servo(s) or am I better off simply replacing them?

If the mode servo is the only issue right now, is it worth replacing all the servos that are accessible while I fix the mode servo? What is the probability that the remaining servo's will fail in the near term?

Am I correct in counting three servos, mode servo, passenger air blend servo and driver air blend servo?

Have the servo designs improved since initial release or will I be putting in exactly the same design that failed?

Thanks for any comments and for all the DIY contributors.

 

Price the servos and your position may change. What you are hearing is the servo constantly trying to change vent position and the system getting worn out ... it will get worse and get stuck in one position. I would suggest let it get to the point that it gets stuck and replace the servos one at a time as the need arises.

Salim

 

I posted a lot on this issue as the air mode servo clicking drove me crazy and Lexus dealers wanted $500 plus to replace. I found a Toyota mechanic working on his own who simply carefully opened the servo and applied dielectric grease to the little wheels inside. I think it's been a year or so and it's mostly remained silent except for a few clicks now and then. Charged me $25. If you are handy it's a simple job other than having to be super careful as you take the servo apart.

 

hi blueman I just finished this DIY today, so I cant speak to how long it will last, but the annoying sounds are gone for now. Took abt 2 hrs for me, hardest part is getting the servos out - some of the screw are a PITA to reach but good assortment of short screwdrivers will go a long way. Once you have the servos out, it takes about 2 minutes to open them and another 15 - 20 to clean, regrease, fix worm gear issue.

Seems there are a few issues - clicking sounds (i think this may be more related to the contacts?) - and that really loud buzzing sound. I dont know how related these two are, but my issue started with the clicking which i could kind of live with. But then I got the really l loud buzzing / grinding intermittently, than permanently in any mode other than feet only - this noise is not something that I could drive around with and also left me stuck with only one position for airflow so I decided to just take a look at both the MODE and TEMP servos in one shot. I modified the worm gear in my MODE servo similiar to the method in the video link below and I believe thats what fixed the buzzing.

Is it worth it? - Like salim mentioned - the parts are pretty pricey for what they are. I decided to take a crack at opening them up to investigate. Worst case scenario I break something and have to buy it. Just be careful and dont force things apart and you should be fine.

Mode servo and passenger ( aka cooling / temperature ) servo are the two easily accessible ones on the passenger side. I think most people have issues with these 2. I didnt bother with the driver side or the air recirulation ones as they weren't giving me problems. (test the air recirc by pressing the button on the dash and listening by the glove box - mine sounded like it was functioning properly without any resistance or clicky sounds)

I believe there are a total of 4 servos (someone please correct me if im wrong)
1. Drivers servo (located drivers side)
2. Mode servo (controlled by pushing mode button to change the direction from where air flows into cabin - face/feet/windshield/combos - located on passenger side farthest from firewall, above passenger servo). I got the loud buzzing from this one - worm gear issue i believe.
3. Passenger servo - aka cooling / temperature (controlled by turning the temp control **** - passenger side underneath mode servo and closer to firewall) I believe this one is where my clicky sounds were coming from.
4. Air re-circulation servo (controlled by button in console to allow fresh air into cabin or recirculate cabin air - passenger side behind CD changer on left)

Pretty sure the design hasn't changed at all.

You can see the play in the worm gear in this video, i had the same thing in my MODE servo. I moved the metal 'collar / yoke' down the shaft like this guy and also put some adhesive where they connect to make sure the worm gear stays in place. Doing both these things, im pretty confident that there will be very little opportunity for it the worm gear to work itself free again, but only time will tell.