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Heater A/c Blower Motor Always Runs At High Speed


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#1 nesierf1

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Posted 26 November 2006 - 04:08 PM

Recently my heater-A/C blower motor just runs at high speed, even if I try to manually adjust the fan speed. The blower motor runs at high speed when cooling or heating, however it will shut off if I turn the heater-A/C off. Lexus RX300, 1999, 130K Miles. Note; both the heater and A/C do heat and cool, just the blower motor is always running at maximum speed. Thanks, Greg B)

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#2 mehullica

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Posted 26 November 2006 - 04:44 PM

Sounds like the blower motor linear contriller has failed. I've replaced many of them. You need to remove the glove box and it's near the blower motor, towards the center of the dash, the blower motor wiring comes from the controller.

#3 mikey00

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Posted 26 November 2006 - 06:39 PM

Recently my heater-A/C blower motor just runs at high speed, even if I try to manually adjust the fan speed. The blower motor runs at high speed when cooling or heating, however it will shut off if I turn the heater-A/C off. Lexus RX300, 1999, 130K Miles. Note; both the heater and A/C do heat and cool, just the blower motor is always running at maximum speed. Thanks, Greg B)

You may want to try just disconnecting the battery cable for a few minutes. Sometimes resetting everything gets you back to normal. This has solved other problems in the hvac area.

#4 ihateduke

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Posted 08 December 2006 - 09:59 AM

I have a similar issue, which may require it's own post. When I have the heat on automatic, it blows out of the wrong ports and it's cold. So instead of it blowing on the floor when it's just starting up, it blows at head level or sometimes through the defrost. If I hit a bump in the road it will jump to the floor or one of the other methods, but then it jumps back in a few seconds.

I'm freezing right now, so any help will be appreciated. If I do have to replace this motor, are there are any online diagrams or instructions on how to do it?

#5 wwest

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Posted 08 December 2006 - 11:46 AM

Recently my heater-A/C blower motor just runs at high speed, even if I try to manually adjust the fan speed. The blower motor runs at high speed when cooling or heating, however it will shut off if I turn the heater-A/C off. Lexus RX300, 1999, 130K Miles. Note; both the heater and A/C do heat and cool, just the blower motor is always running at maximum speed. Thanks, Greg B)


The shop manual indicates taht there is a mechanical heater relay that only applies power to the solid state "blower motor control relay" if the climate control system is turned on. The solid state blower motor control relay uses PWM, Pulse Width Modulation, to vary the average power level to the blower motor and thereby the speed of that motor.

It sound as if the final output drive transister, MOSFET, of the controller is shorted.

#6 wwest

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Posted 08 December 2006 - 12:08 PM

I have a similar issue, which may require it's own post. When I have the heat on automatic, it blows out of the wrong ports and it's cold. So instead of it blowing on the floor when it's just starting up, it blows at head level or sometimes through the defrost. If I hit a bump in the road it will jump to the floor or one of the other methods, but then it jumps back in a few seconds.

I'm freezing right now, so any help will be appreciated. If I do have to replace this motor, are there are any online diagrams or instructions on how to do it?


The NipponDenso engineers who have been designing Toyota and Lexus automatic climate control system have a rather serious shortcoming in their educational level insofar as human comfort factors are concerned. The human comfort equation has a great deal to do with radiant heating effects, not JUST the temperature of the atmosphere surrounding our bodies.

Your body is ALWAYS radiating HEAT outwards, and at the same time being heated by all the surrounding objects that are warm enough to themselves be radiating HEAT. In the wintertime, especially at night, the level of INCOMING heat to your body is minimized and yet these systems still operate as if it were a warm summer day insofar as the radiant heating level of the human body is concerned.

There are a few c-best options that are available in certain models of the RX series, not sure if your 99 has any of them. My 2001 Rx300 has two of those set by the dealer to help alleviate some of the discomforting factors. I can disable, indefinitely, the operation of the A/C compressor by simply switching it off one time. The "link" that results in the automatic operation, with no indication to you of same, of the A/C compressor in defrost/defog/demist mode is severed.

Prior to these two c-best options becoming available, or of my becoming knowledgeable of their availability, I simply disconnect the A/C compressor clutch circuit during the winter months.

Of more recent times, newer than my 2001, a c-best option has become available wherein you can prevent the system from automatically switching from footwell, heating, mode, into cooling mode, cool and dry airflow to the face and upper body. Very, VERY discomforting and in reality, HAZARDOUS.

The Lexus climate control will automatically switch to cooling mode once the cabin atmosphere's air temperature rises to, or nearby, your temperature setpoint. This will not only be somewhat discomforting to your passengers, it might result in allowing the interior windshield surface to decline to the dewpoint of the cabin atmosphere, the point at which condensation will begin to form on that surface.

In cooling mode there is NO LEAKAGE of system airflow to the windshield warming airflow ducts so it will not be unusual at all for the windshield to begin to fog over if the system is left to itself, left in cooling mode, during predominantly cool or COLD weather.

So, do as I do and NEVER allow the system to remain in cooling mode during the cool months, times, of the year. Basically times when the A/C is useless except for the unlikely, highly questionable, possibility of being efficient at dehumidification of the incoming fresh system airflow.

#7 ihateduke

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Posted 08 December 2006 - 12:22 PM

Can anyone post a copy of the service manual for the HVAC system? It's about 20 degrees here now and I want to try and fix this today if possible. I assume I will have to buy the parts from Lexus/Toyota.

Thanks,
Chris

#8 Normal1

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Posted 14 May 2009 - 05:15 PM

Hi

Got the same problem form another angle, my 1998 LS400 a/c blower is set to LOW whatever I try! it is summer and its getting really hot in here! I tried resetting the car by disconnecting the battery but nothing happened!

any ideas!

thanks

#9 luxuspeed

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Posted 16 April 2010 - 03:59 PM

Has anybody come up with a solution to this problem yet? I am having the same troubles, heater/ air conditioning stuck on high speed on all 3 settings. '90 LS 400.

Thanks

#10 lenore

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Posted 16 April 2010 - 08:59 PM

Here is post on Club lexus that gives solution:

http://www.clublexus...speed-only.html

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