ronl1961

I have 03 blowing cold air from heater with temperature set to hot. Had codes checked at auto store and none were detected. Changed out thermostat and still cold air. Anyone have idea as to where to look next? Thanks!!!

lexus114

Sounds like an electronic issue,I think the RX may use for the actual heat control. My mother`s 87 Toyota Celica did the same thing,sometimes it would work though.

salimshah

Unfortunately both tried options were bad.
OBDII codes have to do with operation of the engine (and some extras)
Thermostat (which one?) one in the coolant path has to do with engine temperature control. If your coolant temp indicator in dash is working fine then by observing its behavior you can predict if the thermostat is ok or not.

Back to your problem:

Your issue has to do with either not getting hot coolant in the heater core or control of the dampers which direct air.
Monitor the hose temperature of the inlet and outlet to the core ... look for pipe leading in or out of the firewall on the passenger side.

The dampers are controlled by an ecu/thermostat/temp_control etc. You can try resetting the ecu by disconnecting the battery for 20 minutes or so. A competent mechanic can trouble shoot based on what is working and what is not working. Dealership may be your best bet (assuming they have a competent mechanic) as other shops who are not familiar with RX may have to spend more hours learning than fixing.

Salim

lexus114

Good point.

ronl1961

Thanks! Will check it out this evening and let you know the results.

ronl1961

O.K., checked both heater core inlet and outlet hoses and both were hot. Disconnected neg. battery post for 20 min. and reinstalled. Still blowing cold air. All other functions of controller seem to be working o.k. When temp. is turned to cold, air is blowing from ac vents. When temp is turned to hot, air ports from ac vents to floor vents and defroster works also.(just cold air) Any more thoughts?

lexus114

It`s got to be some sort of temp sensor thing going on their.Do you use the auto position,and just turn off the ac button? If not try that,mine works better temp.wise doing it that way.

sktn77a

iTrader: (2)

Strange that you get no heat when hot coolant is going into and out of the heater core inside the car. This is a strange one!

supra_trd

iTrader: (3)

It might be the heater control valve stuck closed. Get yourself a cable tie and tie the valve open to test your heater.

salimshah

Would he have to break in to the heat exchanger box to get to it?

I think it may be time to take it to an expert.

Salim

ronl1961

I did a ac/heater self diagnostics test that I read about from another post. It showed code 31 and 41. (Air mix door position sensor circuit and air mix door servo motor circuit) Now the problem is, how do I know which one is causing the problem.

sktn77a

iTrader: (2)

????? What's that ??? More info please?

ronl1961

As I understand it the a/c heater control panel has an electronic control unit (ecu) that monitors the systems circuit and stores trouble codes in memory. These codes evidently are stored only in the ecu and are not detected when using an OBDII code reader that was used on my vehicle at Auto Zone. I dont know if this works on all Lexus models but with my RX you can press and hold the Auto and Recirculated air switch at the same time. Wait a couple of seconds and turn on the ignition switch. The display window will flash four times and any codes that are stored in the ecu will show up on the display screen. My codes were 31 and 41. 31 = Air Mix Door Position Sensor circuit and 41= Air mix Door Servomotor Circuit. I have a complete list of all the codes if any one wants me to post them. Im assuming that the air mix door sensor some how reads feed back from the temperature control selector and adjust the position of the air mix door using the servomotor to obtain the selected temperature. So I guess what I am saying is, does any one think that it's the sensor,servo motor or both need to be replaced. Sorry,hope this didn't confuse any one.

salimshah

the on board diagnostic [OBDII .. version two] is a standardized protocol ... the error codes are common to all vehicles. The microcontroller (ECU)stores the sensor information and it can dumped to the reader. The ECU is capable to do more, but the standard readers (all purpose) are not equipped to read say the RX specific codes.

There may even be more than one ECU {For braking system, there is a seperate ecu ... I am not sure if RX has a separate heating/cooling ecu.**

Thank you for posting the dump process.

Salim

RX300malib

So there’s someone else out there with funny temperature issues. I have written in the past regarding the NO HEAT to the drivers side only which is still an issue as winter is upon us here in Conn.

1. If you remove the glove box you can visually see the servos and adjust ***** to see them in action. You can see the servo move the vent door for the heat and adjust the defrost/dash vent/floor board direction diverter.

2. Note the vent behind the glove for the inside/outside air input which is servo 3 of 3.

3. In my 99 model there is a temp sensor just infron of my right knee when driving the vehicle. If you remove the lower panel, you can remove the unit and notice the fan speed change as mine did which I assumed meant it was working.

To this day I have no heat crossing over from the heater box to the driver side which is a pain in the butt. So, I had to be creative a provided a flex hose from the passenger side foot vent and crossed it under the air box over to the driver side foot area. Now my feetsies don't freeze in the way to work.

I suspect that there is a vent door fault inside the air box and I have no plans to remove the entire dashboard in order to investigate or pay the crazy price to replace. I have a 99RX with 180K mile and runs like a champ. Yes the tranny was replaced at 125K.