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a "vent" on RX 350 interior vents

5 messages,  Last post on Jan 18, 2010 at 6:40 PM

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What is this discussion about? Lexus RX 350, SUV

Messages Page 2 of 2

#4 of 5 Re: a "vent" on interior vents [rparis] by delma58

Jan 18, 2010 (2:58 pm)

Replying to: rparis (Jan 18, 2010 10:30 am)
Yes, I can totally close the outer vents near the side window with the rotating button...but then no heat comes out. The inner vents, to the right of the wheel, don't close off but in winter I DO want heat out of these vents . I can direct the inner vents away from me but I'd like some heat on me. What I'm trying to spit out is that there seems to be a wide airflow path and I'd like a more focused one. I know it's possible since I never had this problem in my previous car. ECID! (each car is different)

#5 of 5 Re: a "vent" on interior vents [delma58] by wwest

Jan 18, 2010 (6:40 pm)

Replying to: delma58 (Jan 18, 2010 2:58 pm)
"...I DO want heat out of these vents.."
 
Then I have some really BAD news to share.
 
NipponDenso, Denso US, have US patents involving something they call "dual-layer cabin airflow". The "nut" of this patent is that their HVAC systems are designed to primarily provide airflow for "heating" from the floor airflow outlets. To that end the airflow from the dash and windshield outlets will often be as much as 20F lower than airflow from the footwell outlets.
 
It seems that the basic idea is to provide somewhat coolish and DRY (dehumidified via the A/C) airflow to the upper cabin area (where the windows and windshield reside......DRY airflow) and warmer airflow to the lower cabin area.
 
The arrangement inside the A/C plenum area is such that a high proportion of the airflow destined to exit the dash outlets CAN NEVER pass through the reheat/remix (heater core) system airflow path.
 
Makes it a bit frustrating if you want to raise the temperature of the interior windshield surface well above dewpoint to prevent or remove condensation. To do that you MUST not only switch the system to defrost/defog/demist mode but also raise the temperature setpoint to max heating.
 
My '92 LS400 has a DIY modification inside the climate control module that senses the system being switched to defrost/defog/demist mode and automatically increases the source current (+300 microamps) to the cabin temperature sensing thermistor. Thereby making the system "think" the cabin is suddenly TOO COLD. The system then automatically raises the system outlet airflow temperature and blower speed dramatically.
 
This modification did not work in my '01 F/awd RX300 since DSP, Digital Signal Processing, had been added to the cabin thermistor signal. So I'm left with twisting the temperature control knob clockwise quickly and then activating the defrost/defog/demist mode.
 
Trust me, unless you like sitting in front of, close to, an operating window air conditioner, cool and DRY airflow to your face, neck and upper body, on a cold winter day when the radiant heating effects on you body are virtually NIL, you will find the Lexus HVAC system a lot less discomforting if you remember to over-ride it and keep the system outflow to the footwell.
 
With that dual-layer airflow technique you will need to set the cabin temperature setpoint well above your normal temperature comfort level to get a "comfort" level airflow from the dash outlets.
 
"..I never had this problem in my previous car.."
 
Then your previous car was either pre-1990, undoubtedly of european origin, or from one of the few remaining US manufacturers who do no yet use the Denso US design, horribly FLAWED design.
 
This problem has existed in EVERY Lexus design from the get-go, all Toyota automatic HVAC systems beginning with the same period, and almost all, if not all, modern passenger vehicles of asian origin with automatic climate controls.

Messages Page 2 of 2

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