Rear Air/heat Too Weak, Compared To The Main

[kthan]

I found that rear AC/heat (through the center console) flow becomes too weak, compared to the main(front) Air/heat. I would say only 20-30% air comping through the vent (If I set the main air 100%). Does it mean there's something wrong? Do I need to check some particular things? Thank you for your help in advance.

[Rx330driver]

I found that rear AC/heat (through the center console) flow becomes too weak, compared to the main(front) Air/heat. I would say only 20-30% air comping through the vent (If I set the main air 100%). Does it mean there's something wrong? Do I need to check some particular things? Thank you for your help in advance.

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nope, theres nothing wrong with your car, it happens on all RXs. Just gotta deal with it and set the two vents on the dash towards the back.

[wwest]

Two solutions.

First, the automatic climate control remains in cooling mode when it really shouldn't. Lexus hasn't discovered, nor explored, any way to determine when there is a lack of radiant heating available from the surrounding landscape.

As a result the system remains in cooling mode even on the coldest darkest night when the radiant contribution to your human metabolism is clearly negative.

So, rather than endure the discomfort of cool and dry airflow to the face and upper body of you and your passengers you might want to become more diligent about manually switching these systems into heating mode, footwell airflow(***) in these circumstances.

That will result in WARM airflow from the footwell, front and rear. You might also note that the two dash airflow outlets near the front side windows are not automatically operated and will need to be closed manually if good heating airflow coverage is desired.

*** In cooling mode absolutely NO warming airflow is routed to the windshield. On a rather cold or even cool day that might result in a thoroughly CHILLED interior windshield surface due to impinging COLD airflow due to road speed. When the A/C is automatically disabled at ~35F, or otherwise becomes disfunctional due to climatic conditions, you might be subject to sudden windshield fogging.

So rather than waiting for the system (05 and later) to automatically switch to the windshield warming mode just as the windshield fogging problem is most likely to occur, you might want to pre-empt the system by switching into footwell (some "leakage" to the windshield) mode as the temperature declines below 55F and there is a definite lack of radiant heating effect, then into footwell and windshield combined mode at about 45F.

[kthan]

Thank you for your posts.

wwest, But, what I meant by 20-30% airflow in rear air/heat unit was regardless what air/heat position I set. So, even if I set it to upper body (for maximum air/heat output), the rear unit has only very minimal airflow. This applies to both Air conditioning and heating.

Also, as RX330driver informed, if all RX units are doing this way (with no malfunction), it seems to be pretty disappointing. I am still wondering if this is really the case of $40000 Lexus SUV.

[RX in NC]

Keep in mind that the vast majority of vehicles, regardless of manufacturer, will have much weaker airflow delivery to the back seat passengers than they will to the driver and front-seat passenger. Once the air is conditioned, it must travel much further through relatively inefficient ductwork to get to the back seat, so it will lose blower power as well as heating/cooling capability by the time it arrives to the back seat vents.

Some vehicles with more powerful blowers do a better job of delivering more of the properly-conditioned air to the back seat vents than other vehicles do. Some vehicles have better-insulated ductwork to the back seat than other vehicles do. Unfortunately, the RX appears to have both a weak blower system and poorly-insulated ductwork. The net result is that by the time the conditioned air shows up in the back seat, it has lost much of its ability to do the job.

[wwest]

First, the entire climate control output airflow system is specifically designed such that it is practically impossible to get warming airflow from the upper airflow outlets, especially once the cabin atmosphere has reached or neared the temperature setpoint. I believe that Denso US (NipponDenso Japan) even has US patents on this design concept.

It is not at all unusual for the dash outlets, and windshield frost/defog/demist outlet airflow to be as much as 20F COOLER than footwell flow in otherwise same circumstances. I don't know if you have really checked but I think you will find that the front/rear airflow distribution is much more even in heating mode than in cooling mode, provided you close the manually operated dash outlets as I stated before.

I suspect that the lack of equal cooling airflow to the rear is the result of an intentional design bias since the rear windows all have a reflective coating to prevent radiant heating whereas the front does not.

And part of what you are "fighting" is Lexus' "Pursuit or Perfection". In this case overall quietness of the cabin environment. The entire mold and mildew problem and the instances of sudden windshield fogging all arise from the fact that these vehicles are very well insulated and sealed to prevent wind and road noise. Obviously that also results in very little "flow-through" to keep the cabin atmosphere freshened and from that we sometimes get a dramatic level of mold and mildew spores breeding in the A/C plenum due to the level of moisture often trapped there after a period of A/C operation and of course that also often leads to the many episodes of sudden and instant windshield fogging.

[katzjamr]

Aren't there also heat vents underneath the front seats to heat the floor area of the back as well as the vents coming from the rear of the console? I see vents there when i clean the interior, never felt that area to see what was coming out of it.

[wwest]

Yes, the are airflow "exhaust" ducts under the front seats to route heated airflow to the rear of the car. Like the dash vs footwell in the front the outlets under the front seats are primarily used for heating mode and the console outlets for cooling mode.

Because of the way the airflow in the A/C & heat plenum is routed it is very difficult to get heated airflow to/from any of the "cooling" outlets. Regretably this also includes the windshield defrost/defog/demist airflow outlets.

The only reliable way to get warming airflow to the interior surface of the windshield is in the dedicated mode wherein that becomes the ONLY outlet airflow path.