Last post on Jul 25, 2013 at 4:08 AM
You are in the Toyota Sienna
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Toyota Sienna, Heating / Cooling, Van
#140 of 182 Re: Sienna 2008 Rear Heat Issue [caro1216]
Dec 01, 2010 (9:25 am)
Regretably "They" are correct, your automatic climate conntrol system is operating AS DESIGNED.
NipponDenso/Denso US, actually has a US patent, "two-layer airflow", regarding this aspect of their HVAC designs. Under the patent warm air for heating is ONLY distributed through the floor vents while cooling airflow primarily through the upper vents. Being able to get HEAT from the front "cooling" vents is a compromise of the "two-layer" airflow aspect so the windshield can be heated in cold weather.
There are a couple of C-BEST options that can be an aid. Two of those allow you to disable the A/C compressor for an indefinite period simply by switching it off manually ONE TIME. Second one unlinks A/C from operating automatically in defrost/defog/demist mode. Yet a third option will prevent the system from automatically switching into cooling mode once the cabin atmosphere is raised to your temperature setpoint.
Otherwise you MUST be fully alert and quickly switch the FRONT system back into heating mode once it automatically switches into cooling mode.
In some climatic conditions leaving the A/C enabled will/might be an aid in keeping the windshield defogged or defogging it. But in other climates the use of the A/C will often result in sudden and spontaneous windshield fogging subsequent to the A/C use for defogging.
#141 of 182 Re: 2005 Toyota Sienna Mini Van Heat at idle question [ctbas2005]
Dec 18, 2010 (7:02 pm)
I am also having this exact problem. Can you let me know how you resolved it? Thanks so much.
#142 of 182 Re: Sienna 2008 Rear Heat Issue [wwest]
Dec 20, 2010 (6:04 am)
thanks for replying, but I have one more question. My car doesnt have the automatic climate control system. I have been able to bring the car two more times to the dealer and they have seen the two scenarios in my car. I had put the HOT air and also control the back fron the front panel and COLD air still coming oout fron the rear vents while in the front is HOT HOT HOT. Also, the second scenario, both, front and reas VETNS are HOT HOT HOT, so what is the problem here? They have tried to reproduce the problem with out success. Now, there is a problem if you say there is suppose to be COLD, so why there is HOT HOT air coming out?
#143 of 182 Re: Sienna 2008 Rear Heat Issue [caro1216]
Dec 22, 2010 (4:23 pm)
Carol, on the manual system the rear vents are set up so that upper = cold, lower = hot. I run into that on my own van where my kids will get cold if I forget to switch upper to lower when the weather changes.
As he said it is the designed function. The reasoning is simple: hot air rises, cold air falls so you get maximum mixing into cabin air if you put the hot flow low and cold flow high. Designing the heating coils to go low and cold coils to go high is also a lot simpler and cheaper than designing both to go both ways.
#144 of 182 Re: Sienna 2008 Rear Heat Issue [yatesjo]
Dec 31, 2010 (6:22 am)
Jan 03, 2011 (6:40 am)
Then this is strange. I had checked again the VAN and the rear vents were blowing hot iar between 74 to 84 degrees, and that was only the begining, after running the car for another half hour it reached almost 100. And that is the way it was at the beginifn, the first year I was always in the back of the car, so there is definitly sometihng worng with this car, it doesnt follow a pattern
#146 of 182 Re: '05 Sienna A/C quit working completely [jimox]
Jan 10, 2011 (10:57 pm)
I have the same problem with my Sienna 06. Looks like the whole panel of fuses for A/C, fan, heater, etc (#58-68) is missing. There is, however, a transparent fuse box. There is another fuse panel in the instrument panel, driver side, but I can't figure out how to access it. Do I have to remove the instrument panel to access the fuse box? Thank you very much for the information.
#147 of 182 How do I access the front blower motor?
Jan 21, 2011 (7:04 pm)
I'm pretty sure the front blower motor is bad. How hard is it to change out, and how do I access the blower motor?
#148 of 182 2006 Sienna XLE heater problems
Feb 03, 2011 (7:51 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 182 Re: 2006 Sienna XLE heater problems [unmesh59]
Feb 04, 2011 (10:52 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.