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Heater blowing cold air

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Old 04-20-10, 08:11 PM   #46
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Default Another success

I had my air mix servo go really bad (the gerbil / buzzing noise); so I finally bit the bullet and underwent the DIY replacement. The new part was $116.09 plus $17.41 shipping from parts.com = $135.50. It's a genuine factory part (mfg. by Denso, same as the original).

Yes it was a bit of work and took patience to get all the screws out but it's doable with only a regular Phillips screwdriver and a stubby for the servo (plus a 10 mm wrench for the glove compartment bottom mounting bolts). Plug in the harness before repositioning the servo so that it will move the arm to the proper position. Then position it and re-screw the screws in place.

I now have no more noise PLUS my air mix is working properly for the first time in a long time. I had been putting up with incorrect mix of hot/cold since it was working somewhat. The noise, when it started was intolerable though.

I'd say it took maybe two hours total and I'm not mechanically inclined.

Thanks for all the useful tips here. This forum is great!
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Old 09-18-10, 07:51 AM   #47
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Default Thanks Blueridge

Originally Posted by TxAg85 View Post
Thanks Blueridge; followed your plan with my Code 41 error on my 2000 Rx300. Once in position, confirmed AirMix Servo was culprit. Was not able to adhere to your patience recommendation on the upper screw attachment -- what a tight spot. I ended up using my Dremel tool to remove the top portion of the through hole and slide the servo out from the heater tubes!! Unlike your success, TLC on the servo parts did not work. Ordering part shortly. I did rig a wire to the AirMix lever arm to manually get hot air until the new servo arrives. The picture shows the Air Control Servo and the Air duct that needs to be removed for access to the AirMix Servo (only the "painful" screw is shown on the AirMix Servo just below the Control servo and behind the duct). The two silver heater tubes (also shown) should be hot once the engine warms up.

PS -- First time "poster"; hopefully the picture helps tell the story.
Your photo was a big help. I removed the glove box and the servo. Disassembled the servo (very carefully) and found there was grease all over the contacts. I cleaned and re-installed the servo and it seems to be working fine. My only advice would be to have a small inspection mirror to see the rear screw and to mark the white plastic movement before taking the servo apart.
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Old 09-18-10, 04:33 PM   #48
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Did not have warm air coming for last 2 weeks, even with the temp set to HOT. Could not do the complete work because of the center screw. But things worked and i guess i save myself 300$ with 2 hours of effort. Thanks to everyone who contributed to this thread

- Read this thread
- Removed the glove box.
- Removed the easy access servo (I guess it is called recirculating servo), cleaned it. In the process broke 4 of the delicate plastic hooks holding the 2 parts of the servo together. But i guess that should not be a problem as the outside screws holding the servo would keep these intact together.
- Then tried to remove the difficult servo, could not remove the center screw behind the heat pipes.
- Just manually pushed the outside lever arm coming out of the servo very lightly.
- Tried the set the temp to HOT after putting the key in ignition.
- WOW... The lever moves again and i can get HOT air. So i think it may have been jammed. Hopefully it works for this winters :-)

Not sure how people were able to remove the center screw. It is almost impossible to get to it.
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Old 09-19-10, 02:08 PM   #49
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Default Cleaned both 2 times

I cleaned them twice already. Better at first, but sill messed up. When i send air to the head area it makes a clicking noise. If i turn the blower down and take the strain of the air off of the door then it moves. It will work with the air at the feet and head with no problem. I want to fix it right.

Could someone post a picture with both part numbers so i know which one goes with the part? Thanks alot. i don`t want to order the wrong one. Thanks
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Old 10-10-10, 11:54 AM   #50
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Haven't been on for a long time. Only when I run into problems.

My air flow and modes (blowing at feet, face, defrost) were working correctly, but were only blowing cold air, no heat.

Thanks for all the input. I was able to finally figure out that the gear that switches cold to hot air (aka Air Mix) was jammed. Now that I have unjammed the gear the heat seems to be working fine.

Here is my advice to trouble shoot:
Once you remove the glove box and vent. Turn the car on and play around with the temp and vent controls. You should be able to see the servo motors moving as you switch through the modes and temps.

With the mode button you should notice the servo located on the top moving as you switch trough the modes (from feet, to face to defrost). This is known as the mode servo. Here is the mode servo for RX 99-03 from parts.com

In my case the Air Mix Servo (located under mode servo, the black box closer towards the motor, right behind the 2 metal pipes) was working, it was the gear that was jammed and stuck in the cool position. I turned off the car and gently (with a little force) unhooked the arm of the servo from the plastic gear. I turned the car back on switched through heat and A/C and noticed the servo motor moving the arm. So I knew the Air Mix Servo was working. I turned the car off and put the arm back into the gear and once again turned the car on and tested through the heat and A/C settings.

At this point the gear was unjammed and the heat was working fine. I can see the gear moving as I switched from heat to A/C. I have attached pictures of the gear in action. You will see the gear in the up position in heat mode and the gear in down position in A/C or cool mode. If you unhook the gear from the arm servo and do not see the arm moving then need to replace the Air Mix Servo. The motor of the Air Mix Servo controls the air that switches the gear from heat to cool. Here is the Air Mix Servo for 99-03 RX from parts.com.

Last edited by jtstitzer; 10-10-10 at 11:57 AM.
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Old 10-11-10, 08:27 PM   #51
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Originally Posted by jtstitzer View Post
...If you unhook the gear from the arm servo and do not see the arm moving then need to replace the Air Mix Servo...
If the mix servo arm is not moving it's worth taking the servo out, opening it up, and cleaning the brush contacts. Once you've done this you can test the servo without reinstalling - just re-attach the wiring harness (with the servo out) and switch between cold and heat. Mine worked fine again after doing this
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Old 11-09-10, 01:19 PM   #52
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Default no heat

Beware the anomoly (according to Lexus) of the blend door stuck. Car blows air ok, but no heat. I checked the coolant level, thermostat, air mix servo (thanks for the helpful posts here), lines coming too and from the heat box, flushed the system, and the inside air thermostat. All worked fine and are not part of the problem. Finally took it to the pros...Lexus says the only other thing it could be is the blend door which means pulling the entire dash (13 hrs at $60/hr) and a whole new box ($1700). They say they hardly ever see this...good thing the car is paid for.
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Old 01-23-11, 01:54 PM   #53
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Thumbs up

Thanks much to all who contributed to the thread concerning the cold air when heat is on and identifying the servos as the issue. I had the same problem. I thought the photos below of the servos after taking them apart and identifying the contacts / service areas for cleaning might help others as well.
Attached Thumbnails
Heater blowing cold air-air-mixture-servo-both-halves-photo.jpg   Heater blowing cold air-air-mixture-servo-contacts-photo.jpg   Heater blowing cold air-air-mixture-servo-wheel-photo.jpg  
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Old 01-28-12, 10:25 AM   #54
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Default Do not buy new servos!

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Old 04-19-12, 04:33 AM   #55
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Hello folks-

In my search for Auto Temp control help on Toyota systems- I was led here. At one point I did look at an RX-300 in the boneyard and found many similarities to my system excpet for my lack of dual zone.

I have a 2000 Toy Solara SLE with Auto Temp Control. I have had this issue for the 2 years I've had the vehicle and have replaced ALL sensors, ATC Control Panel, and ETC for EFI switch under hood.

I at least have heat in the morning!!! If I start car and run It appears I have normal heat and granularity of control on the panel. ALL modes appear to be funtioning properly as well.

After a half hour of run time-my output temps seem to be dropping- regardless of set manual or auto. I will set for 77 degrees, and will notice a big drop in temps after the half hour.

In the afternoon on Spring days- the inside of the car warms up with windows closed- I can start car, it'll warm up- but I will have ZERO heat until I have the **** set at 82 degrees. At that point its warm-ish, but by the time it read HOT- I will then have max-heat.

Before I really dug into the problem- I replaced the LCD contol panel- with no affect. I then read about the diagnostics and ran that- getting a code 21 - no biggie run it in sunlight.

I have replaced the outside sensor, the sensor above right knee, and the left side solar sensor. I replaced the ETC for EFI sensor under hood(coolant temp sensor).

I have dug into the Air- Mix Servo that controls the Blend door on the heater box. I can actually hear the door move in minute amounts when cold- as I turn the temp ****. After interior has warmed up in the sun- I can watch for(and hear for) blend door movement- but no movement until the 82 degrees I mentioned. I DID change the Air Mix Servo with another from a Solara and have the EXACT same threshold movement.

It appears there is SOMETHING that is causing the signal to open the blend door to delay as interior warms. My temp guage is in the mddle always, and I feel heat on both sides of the heater core inlet and outlet. These are on the left side of the console. The Air Mix Servo I replaced isright there on the left side of heater box as well.

Has anyone heard of anythign funky like this? I am kind of at wits end and finding a TOY or Lexus dealer to do some level of troubleshoot.

Yes- this is not the time for heat being needed with summer approaching- BUT- this also means that when AC is on- its full AC with ZERO mixing too!!!

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Old 06-18-12, 11:59 AM   #56
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Originally Posted by mindfull View Post
Thanks for this!!! I will be trying this fix this weekend. I am tired of hearing the "Hamsters in their wheel"!
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Old 06-24-12, 12:14 PM   #57
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I have read this whole post, and so far my modes and heat to cold works fine. My problem is similar to the no heat on drivers side only, but mine when in ac mode, get full cold on drivers side but slightly warm on passenger side. This is in all modes, def, face, and floor. Mine does not have dual zone heat, so any ideas what could cause drivers to be functioning properly, get full heat in hot and cold in cold, but passenger gets slightly warm in cold?
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Old 08-01-12, 03:26 PM   #58
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Hereís how I fixed mine after reading https://www.clublexus.com/forums/6965677-post214.html
Took the servo apart as seen in the mindfull pics but instead of gluing the gear to the shaft I glued a piece of plastic to the servo cover. I have these parts trays shown on the left with dividers in them.

I used one of the dividers and cut a piece off about 1/8Ē wide (far Rt Pic). Sanded it down to fit inside the servo case and super glued it in above the gear. Then I replaced everything and it works great. I have had this thing out so many times trying to fix it and now itís finally fixed. 4 months and still working, total cost $0.
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Old 10-01-12, 02:05 PM   #59
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Can I get codes..mine has 21 31 and 41 too.
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Old 10-01-12, 02:41 PM   #60
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Can anyone help me reach screw #1 to open Air Mix servo? I was able to open #2 by using a screwdriver at an angle but unable to reach #1 at all. It is totally blocked by the 2 pipes in front
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250 , air , blowing , blows , cold , dash , duct , es350 , heater , lexus , mix , remove , rx300 , servo , vent

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