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Toyota Sienna Heating / Cooling



  • wwestwwest Posts: 10,706
    Asian vehicles predominantly use climate control designs by NIpponDenso, Denso US here stateside. These systems have long been flawed in that they are unusually prone to interior windshield fogging. Additionally there is NO modern car manufactured that will allow the system to remain in recirculate with the A/C off or disabled. For instance if you encountered an area of outside temperatures nearing 35F in your trip to vegas the A/C would have been disabled automatically even when/if the light came back on when you turned it on manually.

    Since about '01 there have been no less than 4 "fixes" of one type or another to address the issue of sudden and spontaneous interior windshield fogging for Toyota and Lexus vehicles. IMMHO what is really needed, has been needed, is a way to detect that the windshield interior surface is approaching, its temperature is declining, to the dewpoint of the cabin atmosphere.

    I wouldn't be at all surprised if Denso has now added a cabin airflow humidity sensor, or is somehow deriving, computing, Rh from other sensor signals, and thereby automatically switching to "FRESH" mode if the cabin Rh is rising to the level that might result in windshield fogging.

    So yes, a high humidity level in the normally warm daytime coupled with the normally COLD nights in vegas would likely result in a more properly designed system automatically switching out of recirculate mode, especially with 4 or more people on board.

    And my advice would be, regardless of marque, NEVER use recirculate mode during coolish or cold weather absent keeping your interior windshield surface THOROUGHLY HEATED.
  • ateixeiraateixeira Posts: 72,587
    Just recognized your handle from Sienna Club. I'm juice_man over there.
  • caravan2caravan2 Posts: 198
    I have also note that the when I push recycle button, it automatically goes off after a while.

    I was going to complain to the dealer on next service.

    Everyone, please post how your vehicle behaves.

  • bhlhbhlh Posts: 2
    Recently purchased a 2008 Sienna LE with manual A/C system. The air intake selector button seems to default to outside (fresh) air, no matter what position the air flow selector is in. For example if the air flow selecector is set to "panel" or bi-level" on cold days the air selector is defaulted to "fresh" air. If the air intake button is pushed to "Recirculate" then after about 3 minutes it defaults back to "fresh" and you get cool air. After reading page 350 in the manual it says to push the button for at least 2 seconds so it will stay in the "Recirculate" position. But if you go shopping and restart the car it's back to "fresh" again. Is this working as designed ? Is this a design flaw?

    It would seem that in winter conditions if you push the button for "recirculate" the system should stay in that mode (for heat anyway" until the button is pushed for "fresh". In other words it should be a toggle (off or on).

    Has anyone else had this problem? Is there a solution?
  • bhlhbhlh Posts: 2
    I just posted a question about the same problem and then ran across thisw discussion with your reply. Are you saying that the air intake selector (one our 2 month old 2008 Sienna LE) will default to "fresh" no matter how cold it is or even if the heat is not on? Page 350 of the manual says to hold the button in for 2 or more seconds to override the system defaulting to the "fresh" position every 3 to 5 minutes. I was going to take it in to the dealer for repair or replacement but you are saying the system was designed this way. If so, then it is designed poorly as the driver should have the option of making the determination if the button should be set to "Fresh" or "recirculate". Like a toggle off/on switch. I can see it if the A/C is turned on to clear the windows but for those cold mornings I don't like having to push the button in for 2 seconds everytime after starting the car. Poor design.
  • wwestwwest Posts: 10,706
    Since these modern day automatic climate control systems run/use the A/C system all year around it has become more worthwhile to squeeze the very last erg of efficiency from them. So if previously "conditioned" air can be "held" within the cabin for an extended period that would clearly cut back on the workload of the A/C compressor.

    So the exhauster port for cabin air outflow has now been minimized and recirculating up to 30% of the airflow reduces the cabin pressure that would otherwise be created by the blower speed by the same amount.
  • ateixeiraateixeira Posts: 72,587
    I've noticed mine defaults back to "fresh" air whenever the vents for the windshield are open. This is to keep the humid interior air away from the glass, where it might fog up.

    Try yours with the air in the dash only, or feet only, position.
  • OK, we purchased the Toyota Sienna brand new and it's been a great van up to now. We have a little over 40,000 miles on it and the other day the front cabin climate control started behaving badly. The passenger and rear AC/Heat works perfectly, however the drivers side blows a constant cold air, almost as if the temperature selected was 70d F. I have tried all the possible setting combinations and nothing seems to work.

    Note: For the longest time, we heard a rattling or clicking sound in the dash that the dealer could not locate, and now that the left-side climate control is not working that sound is completely gone. Not sure if this was related or not?

    Any idea's?
  • wwestwwest Posts: 10,706
    I would guess that the driver's side solar radiation sensor at the top/front of the dash, bottom of the windsheild, was failing intermittently and that was causing one of the servomotors to continuous "hunt". Now that it has fully failed it thinks the driver is always in BRIGHT sunlight.

    What happens if you set the L/R to "common"..?
  • Well, we don't have a "common" setting other than when a "synch" button that sets the rear and two front air controls (L/R) to the same temperature. I just confirmed that the drivers side heat blows cold on the synch setting as well.

    So if the driver's side solar radiation sensor has failed, is this something that I could purchase and change or am I subject to working with the dealer on this? I am out of warranty and irritated that when we took it to the dealer during the warranty pointing out the sound, they said they couldn't reproduce it.

    I appreciate your advice!
  • stephrstephr Posts: 2
    I've taken my 2006 Sienna in 3 times in a month because I can't control the rear temp from the front. I can only control the fan speed. I have less than 20K miles, and have never had this issue before now. Any one had similar issues? The only way I can control the rear temp is to get in the back and adjust the control.
  • stephrstephr Posts: 2
    Disregard - my dealership tells me that's how it works.....
  • On my 2006 XLE Sienna the air coming from the front air vents remains hot until you switch the temperature down to lowest temperature. Once you set it to low, the A/C will run you out of the van. It you then bump the temperature up one notch, to 65, the air will turn hot again (while on A/C). This happens on both the drivers and passengers side of the van. I haven't checked the rear climate controls to see what happens in the back. This first happened while we were in Texas for Christmas and were going to take the van to dealership down their but it started working again. I figured it wouldn't be worth our time if it's working because they wouldn't be able to identify this issue. The issue has once again pop up it ugly head and our local dealership has being looking at for a day with on good solution. I'm just curious it anybody else has experience this type of issue and if so, what was one to resolve it. Thanks!
  • wwestwwest Posts: 10,706
    You have an open temperature sensor. One of those is the cabin temperatrue sensor just behind that vane window above the driver's right knee. If that is open the control system will sense that the cabin is extremely COLD, regardless of actual, and run the system in heating mode constantly.

    The other possibility, although less likely, would be the OAT sensor being open and the system thinkng that the outside world is extremely cold. If you have an outside temperature indicator you can verify the OAT sensor that way.

    The OAT sensor is usually mounted behind the front bumber but in front of the radiator/condensor stack.
  • Our local dealership spent a complete day looking our van and they now believe they've identified the problem. They said that the cabin temperature sensor was bad and needed replaced. The part is on order and we'll see if this resolve this issue. Thanks, I appreciate your response!
  • mafaustmafaust Posts: 1
    Hi, the rear heat in my Sienna will only blow cold air. I have the manual control system, not the automatic air temp system. With the front fan speed selector on REAR, meaning all the rear system should be controlled by the rear control panel, and the rear temperature selector set to hot and the air flow selector on any of the three choices, I get cold air out of all the upper and lower vents.

    Has anyone else experienced this or does anyone have any ideas as to what is going on/how to address it?

  • shodougshodoug Posts: 1
    The blower motor for the rear AC will not work.

    Since the rear heater blower works fine, I am thinking that the resistor is OK.

    It has been a while since I looked at the wiring diagram, but I remember that there was a relay that selected the ac or the heat blower for the rear. Does anyone know where this relay is located? The diagram did not give out that information.

    I am figuring that it is either the relay, wiring to the blower motor, or the blower motor itself. Are there any other things I should be considering?

    Now that spring is coming, it would be nice to get the ac working everywhere. :)

  • jzx81jzx81 Posts: 3
    I have a 2005 Toyota Sienna with roughly 9k miles on it and the A/C died completely while taking the mom out for Mother's Day yesterday. To make matters worse, the warranty ended two weeks ago and I did not get it extended. The A/C button does not light up when pressed and the blower does not come on at any blower setting level. My mechanic friend said the blower is still getting power when activated by the switch. He suspects the resistor pack is bad that is located close to the blower motor. I had no A/C problems prior to this or any signs leading up to this failure. Anyone have any experience with this problem before or suggestions? Thank you for any input!
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