Last post on Jan 18, 2010 at 6:40 PM
You are in the Lexus RX 300/330/350
What is this discussion about?
Lexus RX 350, SUV
#3 of 5 Re: a "vent" on interior vents [delma58]
Jan 18, 2010 (12:14 pm)
This is sort of like the question of "why disable VSC/TC with a CEL". No one seems to know why, it just IS.
On a Toyota or Lexus the left-most and right-most dash vents are only manually controlled. In the wintertime leaving these open is often desireable provided the climate is conducive to the A/C operation providing some reasonable, substantial level of dehumidification. Only in this case will the A/C operation and leaving these vents open will be of help in keeping the front/side windows free of condensation.
On the other hand the horrible propensity of these NipponDenso and Denso US designed automatic HVAC systems to switch the system AUTOMATICALLY into COOLING mode on the coldest night in the dead of winter does nothing but compound the discomforting effects, along with the increased potential for windshield fogging, with this procedure.
So the best procedure to follow is to manually shut these side dash vents and also be alert to the need to manually switch the system back into heating mode (footwell outflow with minor windshield warming airflow) once it automatically switches into cooling mode. Or even better, manually switch the system into combined heating/defog/demist mode. That position will provide more warming airflow to the windshield interior surface in order to keep those surfaces well above the dewpoint of the cabin atmosphere
You should fine a copy, a FULL and COMPLETE copy, of the various C-BEST options for your vehicle. Among them...the ability to disable the A/C, ENTIRELY disable, defrost/defog/demist mode included.
I NEVER allow the A/C in my vehicles to be used for ANYTHING other than actual cooling. Long ago it was adviseable to use the A/C as an additional aspect, along with HEAT, of windshield condensation prevention or removal, but not with today's IMPROVED, more highly efficient, SPONGE-LIKE A/C evaporator cores.
#4 of 5 Re: a "vent" on interior vents [rparis]
Jan 18, 2010 (2:58 pm)
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]
Jan 18, 2010 (6:40 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.