Has anyone had a problem with their heating and air conditioning system being stuck on full blast? Something in the AC computer system seems to have stopped working to regulate the force that the system blows air. The only exception is when heating, it will not turn on the fan until the car heats up to a certain level... then its full blast. When I turn the right **** down (to manually turn down the fan speed) I see the bars on the display go down, but the fan is still at full blast.

My car is now over 10 years old so some of the systems are acting up and failing. I took it to a local toyota dealership and they said they would have to replace the whole AC computer system at a cost of minimum $850. I've found that most parts can be purchased online at a fraction of the dealer's quotes. So I am considering this option. But first I am trying to understand what part is actually broken and how to correctly identify it online before making the purchase.

Ideas or thoughts? Thanks in advance!


Aaron
1999 RX300 AWD

 

Sounds like it could be the blower motor resistor module. You can do a AC/Heater diagnostics if you 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.
But first things first. Just try disconnecting the battery for a few minutes and see if resetting everything gets it working.

 

Thanks for the quick reply! I recently (August 09) had my alternator replaced. So the battery was unplugged for an extended period of time (at least long enough to reset the date and all of my stereo presets). This problem with the fan popped up last winter so its been around for 10-11 months since it started. I'll try your suggestion and post the results.

 

And always remember to do the diagnostic test in the out door sunlight,or you will get a faulty solar sensor code.(happened to me)

 

I think I spoke too soon on this one. I just checked the service manual and running the diagnostic test won't help. It doesn't really test the blower motor or control module. But after some poking around it looks certain that you need a blower motor control module Part # 87165-22050. It's $188. at newlexusparts.com. Or you could google the part number and maybe find a junk yard one for about $50.
Look here:
https://www.clublexus.com/forums/rx-...peed-only.html

Here is also some info from a Toyota tech forum on troubleshooting the module:
http://forum.ih8mud.com/100-series-c...-question.html

 

I'll provide the results of my test just in case they mean anything to you. They don't mean much to me. I've had the RX for 8 years and am still learning new things!

I put the key in the ignition and set to OFF (one click up from where you can take your key out). I then held down the AC AUTO and the REFRESH buttons for a couple seconds. I then turned the igniton to ON and let go of the buttons. The LCD display went through some test to turn on every light at once. It then flashed the number 00 and then 21 over and over again. I then hit the recirculate button thinking (not sure why) it would stop the test. Instead it went through a series of tests on the AC system. It cycled through 9 or 10 settings (for example 1 turns blower on, 2 blows only one zone, 3 does another zone at a different speed, and so on). I noticed that throughout the steps the blower still blew at full blast even though the test is attempting to run along the whole spectrum of speeds and settings.

Sorry if this is more information than you wanted to know. I found it interesting that it went through this test. Of course when I hit the OFF button, the test ceased.

I'll start searching for the part. I'll be happy if I can get this repaired for under the original quote. I prefer to think of myself as frugal rather than cheap. There's something satisfying about doing some things yourself and getting a better deal!

 

Looks like it passed except for code 21 which is the solar sensor. You can get this code if you run the check when it is dark or if you're in a garage. You usually wont get code 21 if you're in direct sunlight unless the sensor is really bad.

 

And always remember to do the diagnostic test in the out door sunlight,or you will get a faulty solar sensor code.

 

Yes, I saw that note and thank you I actually did test it outside. I'm in north Denver. It was slightly cloudy and around 8am. I may not have been in direct sunlight. But it was shining in my eyes as I was driving east toward my daughter's daycare. During the test I was parked pointing north. I can't recall exactly if trees to the east partially blocked the sun. But I figured since the sun was shining on my car, I would be ok. I'll retest it later just to be sure.

 

It seems like most people running this test get the 21 code. I guess the Solar Sensor is exactly what it sounds like. It detects when the sun is shinning directly on it on it. Even if you are running the test inside a garage, you can verify the sensor by just shinning a flashlight on it. Once the light hits the sensor the flashing 21 code goes away. The sensor is located on the driver's side top of the dash. Just to the right of the small speaker, you will see 2 small black eyes. The one on the right is the solar sensor. The one on the left is the auto headlight sensor.
Now does anyone know excatly what the solar sensor does?

 

does anyone know what code 24 is? I'm having problems with my blower motor controls too. I verified the motor works but it's not getting power.

 

Code 24 on a GS300 is basically the same as a code 21 on the RX.
Solar sensor which was explained in post 7.
This code won't render your blower operation.

Have you checked all your fuses?

 

Yes I've been over all of the fuses, there is only one fuse related to the heater and that is a 10 amp fuse in the drivers side kick panel. I jumped power to the blower, it turns on when I do. I then pulled the blower control module, it is getting a signal from the A/C controls, this signal on the said wire will change voltage depending on what speed is selected so that is working ok. The problem is the power coming into the blower control module is off, there is a relay that supplies power to this module, I now need to locate that relay, I hope thats my problem as if the relay is good then the issue will be coming from body ecu #1 which supplies ground to that relay allowing it to turn on.

 

Sorry for the late response:

HTR Relay is located in the pass kick panel junction block.
Right next to the deffoger relay.
All the way on the top of the junction block. 5 prong I believe.

Just to let you know that the Htr relay when energized. Get's power from a 50amp medium current fuse located in the engine compartment pass. side. If this is blown. you also won't get power to the blower control module.

 

Thanks for the reply, yes we tested the relay today and it's good, I also tried a set of A/C controls from my local wrecking yard with no luck... When we jumped the relay it activated and sent 12 volts to the blower control module (BCM), but even with the blower control module getting power the blower motor still doesn't turn on, the smaller ecu wire on the BCM must either not be sending the correct signal to the BCM to allow the power to pass through tot he blower motor or the BCM is bad. If that's the case I think I have a bad body ECU 1 and a bad BCM.. I hope thats not the case. Also the Engine ECU is also involved in turning on the blower motor per the electrical diagram. I hate these multiplex networks.. BTW my car is a 2001 Lexus GS300, similar to the RX.