Last post on Dec 02, 2012 at 9:08 PM
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Toyota Sienna, Heating / Cooling, Van
#148 of 179 2006 Sienna XLE heater problems
Feb 03, 2011 (8:51 pm)
Having gone through this whole thread, I'm beginning to wonder of the climate control is behaving as designed.
The front vents are nicely blowing hot air as we go down the highway when suddenly, they start blowing cold air. To get warm air again, we have to jack up the temp settings extremely high which causes it to blow *very* hot air and we have to dial down the settings to their usual position. The cycle then repeats.
Somehow, we don't remember it behaving this way in previous winters but it may have.
The other and possibly related problem is that the air from the upper vents is not as warm at a given setting, say 72-deg, as our other cars. As per this thread, this might be as per design.
Don't even get me started on the fogging of the interior glass surfaces!
The dealer found nothing wrong the last couple of times.
Are there C_BEST (what the heck is that any way?) settings that might get the system the way we expect it to i.e. not be overly intelligent? I have a service visit coming up.
#149 of 179 Re: 2006 Sienna XLE heater problems [unmesh59]
Feb 04, 2011 (11:52 am)
New models of the NipponDenso HVAC system will automatically switch modes if/when the OAT declines to/below about 35F. At that point the A/C is disabled and the "target" outflow temperature is raised in order to prevent windshield fogging since the A/C dehumidification functionality is off.
You don't say so but I am of the understanding that along with the above, the system also automatically switches to footwell outflow mode, away from "dash" outflow. Only in footwell or partial footwell/windshield mode is any level of warming airflow routed to the interior surface of the windshield.
There is a C-best option, serveral actually, that can be helpful.
1) The A/C can be disabled indefinitely simply by switching it OFF once. It will not activate again, EVER, until you switch it back on. I always have. leave, my A/C disabled throughout the winter period, only have it enabled for actual COOLING requirement.
2) The A/C can be unlinked from automatic operation in defrost/defog/demist mode. Mind is ALWAYS set so.
3) The system can be prevented from switching to cooling mode, dash outflow, automatically once the cabin temperature has risen to, or nearby, the temperature setpoint. There is NO warming airflow to the windshield in cooling mode(***). I do not have this C-best option, '01 F/awd RX300, so I must be fairly diligent in monitoring the system to prevent this switch.
Use of these measures will help dramatically to prevent interior windshield fogging when the OAT is below ~47F and the dehunidification capability of the A/C is mostly, often, non-functional.
If the windshield should fog up, say due to "loading" a couple of wet and sweaty snow skiiers, turn the heat up to MAX and use the windshield defrost/defog/demist mode.
Try to use the A/C and it may, or may not, be functional, but even worse when it subsequently switches off the moisture previously accumulated on the ~10,000 sq. in. of evaporator surface vane area will now become free to evaporate into the cabin.
*** outlet airflow from the upper, dash, and windshield vents will often be as much a 20F lower than airflow from the footwell vents. NipponDenso has a US patent pertaining to their two-layer airflow technique.
#150 of 179 Re: Toyota Sienna: Cold & Hot Air Flow [rookie9]
Feb 22, 2011 (12:20 pm)
This might help clear things up for anyone that still has this question. The Sienna is DESIGNED to have the UPPER (ceiling) rear vents blow cold/AC air ONLY. The BOTTOM (floor) rear vents are the only vents that can blow warm/hot air. If you wish to heat the rear area (in a Sienna with a manual system), turn the fan speed selector (the one located on the dashboard) to "rear." On the rear control panel (located above the driver side captain seat/first row seat), select the foot air flow selector, turn the temp knob all the way to the right, and select the desired fan speed. Place your hand over the FLOOR vents. If the air is not warm/hot after 10 minutes of highway driving (15 mins side road), then you have a problem.
#151 of 179 Re: Toyota Sienna: Cold & Hot Air Flow [nicko333]
Feb 22, 2011 (5:03 pm)
On my 2005 Sienna with manual heater/air conditioner controls the air temperature from the upper and lower rear vents is the same - warm/hot when using the heater and cold when using the air conditioner. In addition I can find nothing in the owner's manual stating anything different.
#152 of 179 Re: Toyota Sienna: Cold & Hot Air Flow [nicko333]
Feb 23, 2011 (10:03 am)
You CAN get heated airflow from the dash/upper vents AND the windshield vents but only via somewhat extreme measures. Turn the temperature setpoint all the way to MAX heat and manually select dash vents or defrost/defog/demist position.
That latter mode is how I most quickly defog the interior windshield surface.
#153 of 179 Re: Toyota Sienna: Cold & Hot Air Flow [relooky01]
Feb 23, 2011 (10:06 am)
Yes, the owners manual only hints at the issue. If you read the factory shop/repair manual's information on the operation of the HVAC system then it becomes much easier to understand, clarify, the information in the owners manual.
#154 of 179 2004 Sienna A/C selector and Air intake selector problem
Mar 26, 2011 (4:16 pm)
I have noticed that my 2004 Sienna manual A/C system has the following problem recently:
1. When I turn on A/C, the A/C selector light is on, some cold air comes out.
2. After 5-10 minutes, the air intake selector light automatically turns on, which indicates that it recirculates the air inside the car.
3. While A/C is on, I could not turn the air intake selector light off unless I turn the A/C off.
4. If I don't turn on the A/C, I can tune on/off air intake selector freely.
Has anyone any idea what is wrong? Is it an expensive repair?
#155 of 179 Re: 2004 Sienna A/C selector and Air intake selector problem [xsssssss1]
Mar 27, 2011 (9:13 am)
A bit backwards but....
As a SAFETY measure recirculate will NOT remain on unless the A/C is operational. In recirculate mode there is a danger that the cabin atmosphere RH, Relative Humidity, will rise high enough (due to human metabolism, breathing, perpiration, etc.) to fog the windshield.
With the A/C operational there is generally enough dehumidification capability that the safety concerns are alleviated.
#156 of 179 2006 XLE A/C Climate Control
Aug 04, 2011 (2:58 pm)
Owned van since 12/10 -had 34Kmi, now 39K. I need help.
Turning the Ignition to the ON position, I hear lots of noise coming from the passenger side of the console - as though there are stepping motors trying to reset to a "zero" position which they fail to find. Seems like it needs an input from a sensor ... to complete the loop - it may be related to the A/C system. Thx.
#157 of 179 Automatic A/ Csystem sienna 2006xle.
Aug 16, 2011 (9:00 pm)
I am still trying to figure out why the front a/c unit - with the ign switch to ON -
engine not running, i hear a (stepper?) motor eager to find its reset point never finding it,
mixing short stops with short run 'excursions" .
Today I noticed that the rear A/C panel's "auto mode" is stuck ON as indicated by its green LED ; i cannot "deselect" it. Could this be related to the above ?
Will someone tell me what is the state of the rear a/c panel lighs when the engine is tuned ON with no front A/C panel selection functions selected ?
I went to the dlr: serv advisor " you have no problem..."
Any ideas welcome. Thanks.