Hi all

2007 TCH

This been bugging me for quite some time. My experience with Japanese vehicles is that no matter how you direct blower air flow, windshield and window vents still have air passing through them. Which is fine, I do understand why.
But here's the thing. I have my Plazmacluster set to 70 degrees. Air direction is windshield and floor, my standard favorite.
My feet are nice and warm, no problems there. But the side, far left vent in the dash, starts with warm air, and in about 30 minutes of driving, starts cycling warm-lukewarm-warm-lukewarm. Not cold, no, just kinda - lukewarm.
Say, I raise temp by a degree or 2 - that vent will stay warm for longer time, then goes back to cycling.
Now, I do not want to blame it on something broken, as my wife's 99 Lexus RX300 - does same thing. Looks like it is simply designed that way.

Thoughts?

 

What you are experiencing is the market domination beginning in the early 90's for automatic climate control system designs and production by NipponDenso, Denso US.

A very FLAWED design.

The basic problem is that once the cabin temperature rises to within a few degrees of your temperature setpoint the system will switch into cooling mode, Coolish, COOL airflow, to those side window vents, and NO airflow at all to the interior surface of the windshield to help keep it above dewpoint.

My '01 RX has options that can only be set by the dealer that allow me to turn off the A/C for an indefinite period, plus unlink the A/C from automatic operation in defog/demist/defrost mode. In certain climatic conditions, often occurring here in the pacific NW, A/C operation can prove to be EXTREMELY HAZARDOUS.

Absent having these options set opposite the factory default, your wife should be very diligent in turning off the A/C during the winter months, especially so immediately after activating the defrost/defog/demist mode. I would also suggest diligence in keeping the system in heating mode, footwell airflow, at all times other than those requiring actual A/C cooling. Otherwise the system will ALWAYS shift into cooling mode, absolutely NO warming airflow to the interior surface of the windshield, once the cabin temperature rises to nearby the temperature setpoint.

Additionally, should the windshield interior surface EVER fog over while underway, or even BEGIN to do so, she should IMMEDIATELY raise the temperature setpoint to MAX HEAT and THEN switch to defrost/defog/demist mode. Absent the use of that procedure the system will rely ONLY on the A/C dehumidification capability for defogging the interior windshield surface, a capability that may not exist in certain climatic conditions. Even worse the system itself may actually be at fault for windshield fogging, SUDDEN, unexpected windshield fogging.

The A/C operation will be automatically disabled should you drive into an area of nearly freezing, freezing, or sub-freezing climate, releasing ALL of the previously condensed moisture into the otherwise COLD and DRY incoming outside atmosphere. That's just one of the reasons for keeping the A/C disabled, TOTALLY disabled, during the non-cooling use period.

For yourself I think more modern day Denso climate control systems have about 3 or 4 options which impinge on this same area, even one that prevents the system from switching automatically to cooling mode, and another that changes the overall system operation once the OAT declines to near or below freezing.

Most dealers will deny the existence of these options, you will have to be persistent.

 

Oh, also, you can improve the RX's A/C efficiency fairly dramatically, and also improve the FE somewhat, by turning off the flow of engine coolant to the heater during times of A/C cooling need/use. Purchase/install a manual water flow control valve at Home Depot, etc.

 

Constent from/thru '91, '92, '95 LS400, '00 GS300, '00 RX300, '01 RX300. Coolish airflow, as much as 20F lower, to the side vents AND the windshield defrost/defog/demist mode(***) once the cabin atmosphere rises to nearby your setpoint. I suggest that you always close those manually during/throughout the winter, non-cooling, period.

*** NO windshield warming airflow whatsoever except as manually directed, overridden, combined footwell/windshield.

 

good response, man. well, what can I say... just shake my heads. how is it that designers always "know better" what end user wants? and in some odd, inhumane way?
it's really no big deal, I am not cold. except that it's truly psychological thing - you turn heat on, set it to 70, it's all nice and dandy, suddenly, you get that wiff of cold air onto your hands on steering wheel. panic! something's broken!!
no, it's just dummass design.
to make things better, with all them electronics controlling car "for you", you can't really even adjust anything the way YOU want it. said it before - LOVE my Silverado in that respect. Large mechanical *****, set it which ever way you please. only have to watch window mode, as a/c kicks in.

 

well guess what.. i fixed the problem.
I simply really got ticked with cold air blowing out of driver side dashboard vent yesterday.
so, I basically shut down the large vent in the dashboard left hand side. well, fair enough, this only made issue worse, but allowed me to determine that cold air is blowing from a small triangular window vent that is right above the large rectangular vent.
for what it is, I would have sworn that both vents should be same temperature and on the same air hose, appears, my guess is wrong.
I used simple and proven technique - taped that small vent over with tape. yepp.
guess what - driving back home from work, for about an hour, had nothing but nice warm air coming out of the large rectangular vent. I opened it. how does this work, I'll leave it to those Japanese geniuses that managed to come up with this. I can only shake my head in disbelief.....

 

That might have been pure happenstance, the newer system operates differently(***) if the OAT is below ~35F and remains below 35F for your entire hour drive.

I modified the OAT sensor in my '92 LS such that it "sensed" 28F throughout the winter months. No OAT display in '92.

*** Disables the A/C compressor entirely, and even newer('08+[??]) systems automatically remain in heating mode.

 

well, for starters, I do not run automatic climate control. virtually never.
what I do not understand is how that triangular vent manages to blow cold air, whilst one 6mm below it blows hot. unless they were stupid enough to run a separate air duct to it. but WHY????????????????

btw, west, I have no idea what you just said. sorry.

 

Other than turning the system to max heat, max cooling, or COMPLETELY OFF, I don't think there is any way to avoid automatic operation of at least some, minimum of one, of the system functions.

I suspect that the airflow vent to that triangular window, and the side window (duct in the door) is part of the windshield distribution whereas the vent just below on the dash is genral cabin distribution. I'll have a look at the shop manuals later this morning and report.

 

Okay, here's what I can tell you factually. On my '01 F/awd RX300 the slot duct in the side window and the one in the small triangular window are extensions of the windshield defrost/demist/defog airflow ducting. As long as the system is in heating mode, footwell ONLY outlet airflow, there will be a fairly low level of airflow to the windshield ducting. If you allow the system to switch into cooling mode, primarily center dash airflow, then there will be NO airflow to the windshield ducting.

The large far left and far right dash outlet vents are NEVER closed automatically.

Later Toyota and Lexus models did some kind of system reconfiguration, moreso than just A/C disable, if, or as, the OAT declined below freezing. I believe I remember reading that the reconfiguration involved something pertaining to keeping the windshield above dewpoint since the A/C could no longer dehumidify the incoming airflow.

Keep in mind that as long as the system is on then functions that you have not manually over-ridden will continue to be automatically controlled. I suspect that you cannot over-ride the reconfiguration aspects with the OAT at or below freezing as that can be, has proven to be, hazardous.

Sudden, seemingly spontaneous, FULL windshield fogging that cannot be quickly overcome.

On my '92 LS400 the inlet airflow might indicate "fresh" but I was to discover that unless I manually selected fresh mode the system would automatically modulate between fresh and recirculate depending on overall conditions. Obviously there was no way to know which mode it was in absent my remembering if i had or had not.