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lexpert, Lexus Master tech
Category: Lexus
Satisfied Customers: 9974
Experience:  Master Certified with lexus, 8 years experience with Lexus
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2001 RX300: Fan works, AC works, but when I increase temp..cold air

Customer Question

2001 RX300. No heat from the heater. Fan works, AC works, but when I increase temp to max nothing happens just cold air.
Submitted: 9 years ago.
Category: Lexus
Expert:  lexpert replied 9 years ago.

Hello and thank you for using just answer. A few questions to better help you here and narrow this down. First does the vent mode function work normally to cycle vent positions?

As far as the hot/cold issue does this symptom occur on both sides/zones of the vehicle or only the driver side? Do you hear any unusual noises such as clicking or grinding under the dash when you cycle from hot to cold?

Customer: replied 9 years ago.
Not sure what vent mode is, but I've noticed when I turn the system off outside air still comes through the vents.

The sympton occurs on both sides. No noises.
Expert:  lexpert replied 9 years ago.

By vent mode I mean position, there is a button on the climate control face plate that has controls vent postion (which vents the air comes out of).....face vents, floor vents, defrost or blended, was wanting to know if you can manually command the different vent positions.

By design you will always have some air coming out of the vents at road speed unless you manually command recirculation mode, the fresh air vents have air forced through the fresh air intake unless you seal it off by commanding recirculation.

If you cannot command heat/cold to operate then you need to start by inspecting the air mix servo motor under the dash to see if the servo motor is acting up or if this is an internal issue in the blower unit for the air mix door. It is somewhat common for the vent mode servo motors to fail on this vehicle but not as common for the air mix servo to fail. let me know if you would like some diagrams or further information on this.

Customer: replied 9 years ago.
Yes I can manually change the vent positions with vent control.
Directions and Diagrams would be helpful so I know where to look and what I'm looking for.
Expert:  lexpert replied 9 years ago.

Thank you for the reply, several items fo ryou then, you are dealing with an air mix servo issue, click these links for some help:




Download 2


Download 3


Download 4


Download 5


Check for codes and then for physical operation of the servo.

Customer: replied 9 years ago.
I checked under the dash The pipes are hot, but the air mix sensor arm doesn't move. I checked the fuses and they are all ok.
Expert:  lexpert replied 9 years ago.
Check for codes then and test for power supply to the servo motor. There are 2 servos in that area so be sure you are testing the right one, one moves when you command vent position and the other one moves when you move from hot/cold.
Customer: replied 9 years ago.
It's the servo that moves hot/cold. Is there an easy way to test for power supply. it's real tough getting at this servo especially finding the power leads. Do I have to remove the front panel?
Expert:  lexpert replied 9 years ago.

Sorry there is no easy way to get to this one, technically the manual is going to want you to pull the dash and the housing to service it out of car but with the right tools and patience you can better access this in the vehicle. If you have verified the servo does not respond then 1 of 3 issues: 1- bad servo 2- heat flap inside the housing is jammed and holding the servo in position 3- no power to the servo from the control head.


Note if you have an internal flap jam you should have at least a "twitching" action from the servo when commanded.

Customer: replied 9 years ago.
There is no twitching. Should I try to gently force it with a bit of pressure on the arm to see if it moves?

Is there an easy to check if it's getting power.

Failing all of the above then it's a bad servo. Keeping in mind I'm not a mechanic, can I replace it or should I take it to Toyota.
Expert:  lexpert replied 9 years ago.
This repair is best performed by a Lexus or toyota technician if you are not experienced in this, you can save some $ by diagnosing yourself though if you are capable of reaching the connector. No don't try to force the arm. If you can get the electrical connector off the servo you can test for power/ground to see if this is a servo issue or a controller issue.
Customer: replied 9 years ago.
I can't get at the electrical connector. There are no Lexus dealers within 100 miles. I gave the info you provided to the local Toyota dealer and they said they'll take a look next week.
Expert:  lexpert replied 9 years ago.
Ok, let me know if you need further help with this one.Thanks
Customer: replied 9 years ago.
You're not going to believe this. But all of a sudden i have heat! The only thing I can think of is when I asked you if I should try forcing the servo arm, I tried moving it with my fingers and it seemed pretty well locked up, but i was able to move it back and forth about an eighth of an inch, but at the time nothing else happened. I should note I bought the car in Florada this year and therefore its possible the heat was never used, so maybe the damper was just stuch from lack of use. My guess is maybe by trying to move the arm, for whatever reason it finally came unstuck.
Expert:  lexpert replied 9 years ago.
That is may want to try cycling the heat back and forth several times if this is the case however if this is the case there is a possibilit that the servo is weak/worn and you should be prepared to have it replaced if it acts up again. Is there anything else you need hel;p with on this for now?
lexpert and 3 other Lexus Specialists are ready to help you
Customer: replied 6 years ago.
It's been 2 years and I just wanted to update you further in case you get similar requests.

Occasionally the hot/cold still gets stuck in one or the other mode and I hear clicking sounds under the dash. I think its the servo arm/gear trying to open/close the flap which is continually getting stuck. Eventually it gets unstuck and I get heat (or cold). So far I can live with it but I'm guessing the servo will eventually give up.