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Toyota Sienna Heating / Cooling



  • wwestwwest Posts: 10,706
    Once the engine coolant rises to the normal operating level it should NOT move.

    More likely than not your coolant is low, the engine is "threatening" to overheat and with the engine at idle no coolant flow gets to the heater core.

    You should NEVER use recirculate at any time that A/C cooling is not required/used.
  • alezwellalezwell Posts: 1
    I bought my van in Nov 2009. Currently it has mileage of approx 4000 mi. Recently I started observing that not enough heat is coming when the temp (inside) is set to 71/72 (F) AUTO, and outside temp is cold (around 31 to 32 F). Some times I am feeling too much heat at 68 (Auto). This is not happening on regular basis. I want to take my vehicle to the dealer. How ever I as wondering how to reproduce this problem as it happens occasionally. Any advise on this highly appreciated.

  • doelkedoelke Posts: 2
    wwest was right - low coolant level was the culprit.... now I feel silly for not checking that first.
  • wwestwwest Posts: 10,706
    The climate control in your Sienna relies SOLELY on the control of the cabin air temperature to adjust to your comfort level.

    But the human comfort equation relies on more than surrounding cabin air temperature. The lack of radiant heating from a COLD surrounding landscape, OUTSIDE surrounding landscape, can have a seriously adverse effect on your comfort level.

    There are several C-best options that your dealer can set that might be of help. The system can be set such that you can disable the A/C for an indefinite period, throughout the winter period, for instance. Set both of these opposite the factory default.

    A relatively new one is the ability to have the system remain in heating mode should outside climatic conditions dictate. Otherwise the system will automatically shift into COOLING mode, coolish and dry outlet airflow to your face, neck and upper body, once the cabin temperature as risen to a close range of your control setpoint.

    Somewhat discomforting to say the least.

    Yes another idiot design from our "friends" at NipponDenso, the company that has now brought us the UA episodes.
  • lhmadmanlhmadman Posts: 1
    Hi, I'm a noob here, so please be gentle. :blush:

    I have a 2010 Sienna XLE. Over the last couple days, the climate control setting have changed upon restarting the car. In one case, my wife turned on the car and the fan was blowing full blast. We never run the fan any higher than speed 1 or 2. On two other occasions, it changed from external air to internal air recirculation. In all 3 cases, these changes occurred after starting the car.

    Someone suggested elsewhere that the automatic climate control system might set itself to bring the interior of the car to the previous temperature setting. However, in all 3 cases, the car had only been stopped for a short period - just long enough to pick up a kid at preschool. So there wasn't a tremendous change in interior temperature that would necessitate a sudden change in fan or air source settings. Also, this never happened during the summer, when the interior got really hot - the AC didn't automatically start going full tilt upon starting the car.

    Because of the well-publicized recall of other Toyota models, and the revelation that the acceleration problems may not be entirely due to sticky accelerator pedals but possibly due to electrical or computer problems, I'm concerned that what I'm seeing is a symptom of a problem in my Sienna.

    Has anyone had similar experiences, or any specific advice? I'm thinking about bringing it in for a service check.

  • toni999toni999 Posts: 2
    2004 Sienna has vent position stuck in the front position and no heat. Rear system does not respond to any control settings either. Recirculate function and AC works, but no heat. I' d appreciate advice before I bring it to the dealer. AC/vent control box lists for almost $900 online and I'd hate to have to pay that much if that isn't the problem. Thanks.
  • wwestwwest Posts: 10,706
    "..been stopped for a short period.."

    In cold climates this situation, "stopped for short period" represents the greatest propensity for quickly fogging over the interior surface of the windshield shortly after restarting the car and driving away.

    There are clear indications that Toyota/NipponDenso has begun to pay more attention to this issue as the 2010 systems will now automatically switch back into heating mode, or even heating/defrost/defog/demist combined mode should climatic conditions so dictate.

    What you are seeing might be the result of NipponDenso's newfound focus on these problems.

    These systems make use of the A/C system all year around, in the wintertime primarily for dehumidification of cabin airflow as a preventive measure against windshield fogging. The problem is that during that use lots of moisture is condensed onto the 10,000 square inches of evaporator vane surface area. As it happens much of it will remain there even overnight if some preventive measure isn't made/taken.

    Read about the EED, Electronic Evaporator Dryer, at for a good tutorial.

    So the HIGH fan/blower speed upon re-entering/restarting the car may be Toyota/NipponDenso's answer to a long standing, VERY long standing (1990 and on...) problem with their automatic climate control systems.

    I guess I'm sort of surprised that the rear windows aren't lowered ever so slightly at the same time the blower speed is raised. Actually, have you checked to see of the rear "winglet" windows aren't automatically opened slightly at the same time? If not that might be a practice you will want to take on manually.
  • hsladyrosehsladyrose Posts: 2
    I am having a similar issue with our 2005 Sienna. It started out with not blowing cold when I'd have a/c on..and I'd have to turn it off and then turn it back on to get the cold air to engage. Frustrating! Well then, the front fans stopped workinge entirely, but rear ones still work.

    Do you think this also might attribute to the same switch you found? I'd hate to have to pay toyota an arm and freakin leg to get this fixed if all I need is to replace a relay switch. What did you end up doing? Or did you just sell the lame thing?

  • toni999toni999 Posts: 2
    Problem wasnt relay switch. Even worse it was the whole control module for the heating and vent system ($630.00!!!!!). Aaaargh ... I had it repaired anyway and all is well since then. Still better than having to male new car payments.
  • mfc3mfc3 Posts: 8
    I would think so. You can get a relay from dealer for $18.
  • khardingkharding Posts: 5
    Yes, I would try to change out the specific relay that controls the front fan and see if that fixes the problem. I think this relay cost me about $15-20 a year or so ago, and that solved the problem. You will need to check the owners manual to see which relay controls what function, and then replace that relay. Good Luck.
  • deepee1deepee1 Posts: 1
    The rear fan in my 05 Sienna stopped working completely. Niether hot not AC no way it does not budge. The front vents do work properly with Heater as well as AC. Not sure where to look. Possibly a relay or a fuse but no idea how to find. Any help would be appreciated.
  • khardingkharding Posts: 5
    First of all, check the owners manual. There is usually a numbered diagram of the relays that correspond to a list of relays and their function. Find the one for the rear fan. When I had my problem, it was not the AC or the heat, just the fan that stopped working. I believe that this relay box is located in the engine compartment, under the hood, but I am not positive. It should tell you in the Owners Manual. There is usually a protective cover that needs to be removed. You will see the relays similar to the diagram in the book. Pull the bad one out and plug the new one in. Most autoparts stores should have these in stock.
  • arprincearprince Posts: 3
    2001 Sienna. Heater is OK. Blower is OK. But AC does not work. I refilled coolant and AC worked for 2 months. Then it would just blow air afterwards. When I checked the coolant, the dispenser which has an electornic guage says that the coolant is full.

    Injected a dye but see no leak. Any other tips for troubleshooting?

    Thank you.
  • wwestwwest Posts: 10,706
    If the compressor clutch cycles on and off at all then you do not have low refrigerant, at least not seriously so.

    So, is the compressor clutch cycling or continuously engaged..?
  • arprincearprince Posts: 3
    I don't think the CC cycles at all. On the refrigerant canister (located at the engine) where you can see the refrigerant flowing on the small circular glass window, I see a good flow however.

    On my matrix, the aluminum pipes (with the H) goes cold and the CC cycles. On my sienna, it does not go cold at all. Is there a fuse for the compressor I can change or something? TIA
  • wwestwwest Posts: 10,706
    "...I see a good flow however.."

    The only way I know to see "flow" in that sight glass is to have observed the transition from gas to bubbles to liquid as the compressor cycles on and then from liquid to bubbles to gas once the compressor cycles off.

    If you are seeing flow then that is really good news as that would mean the refrigerant is going through the complete HVAC cycle. Evaporative cooling in the evaporator and then compression and heat removal in the condensor.

    In that case you may have a heat/cooling reheat/remix control door/vane/damper stuck in the FULL HEAT mode.
  • karrollekarrolle Posts: 1
    my ac seems to be working in the rear ceiling vents, but the front is only blowing out hot air.
    any ideas as to how this could be happening?
    thx much
  • gedgoudaslgedgoudasl Posts: 21
    I had the reverse problem, front A/C while rear was heating. My problem was rear AC wiring harness was unplugged. The print out diagnosis showed rear was experiencing 40 degree temperatures so the system turned on the heat (110 degrees) in the rear while the front was putting out cold air (40 degrees). So something is telling the computer the front is cold and it is turning on the heat while cooling the rear.
    Hope this helps.
  • johnqvanjohnqvan Posts: 1
    I had a new battery put in today. It may or may not have anything to do with the problem, but it seems to have started right after the battery was changed. Now the compressor turns on and off quickly. Sometimes it only cycles once or twice, sometimes 10 or 20 times. When driving at full speed the A/C cools fine. At lower speeds, not so good. Both fans at the condenser coil and radiator are working. When the car is idling you can see the RPM gauge dipping with the engaging and disengaging of the compressor. Could this have anything to do with the battery change? It was 91 degrees today when it was at it worst. Tonight, at 78 degrees, it would turn on, then off, then on and stay on. Any suggestions?
  • dfinndfinn Posts: 1
    I have the same problem. I have a 2005 Sienna, the AC works great on the passenger side but only blows hot air on the drivers side. Any suggestions on how to correct this issue? Thanks for the help.
  • wwestwwest Posts: 10,706
    edited June 2010
    Recirculate mode CANNOT be over-ridden if MAX cooling is being used.

    Sienna start-up procedure after setting in bright Tampa sunlight:

    A) Open the rear quarter panel venting windows.

    B) Turn the A/C on, the blower to maximum and the temperature control just a tad, one "click/notch", below maximum cooling.

    C) disable recirculate mode.

    Once the previously heated cabin atmosphere, HOT cabin atmosphere, is purged then close the rear vents and return the temperature setting to maximum cooling (the system will automatically go into recirculate) and use the blower speed to set/maintain your comfort level.

    I also ran the rear A/C blower on low most of the week we were in FL but much of the time the 2010-11 Sienna could not quite overcome the FL heat. Running the system on maximum cooling yields the best A/C efficiency (bypasses the reheat/remix airflow path) and FE.
  • eimaraleimaral Posts: 4
    Hi there,

    I have a 98 Toyota Sienna with just over 100k miles on it. For the past one year or something, when I turn on air conditioner, it will produce a loud squeaking noise for about 10-15 seconds. The harder you step on the gas pedal the louder and faster (higher frequency) the noise gets. But it diminishes after ~15 seconds. The air conditioner itself works fine, blowing out cold air with no problem. So, could it be alternator? Belt? even battery? Please shine a light. I really don’t want be pushed around by dealer mechanics with some $2,000 estimate. Thank you.

  • wwestwwest Posts: 10,706
    Most likely the drive belt driving the A/C compressor but a distinct possibility of the A/C compressor clutch itself beginning to fail.
  • eimaraleimaral Posts: 4
    Oh, then it sounds like we need to replace the compressor. Won't be a cheap fix......Thank you very much, WWEST!......But.....will it be workable to just replace the clutch?
  • wwestwwest Posts: 10,706
    No, it would be too inexpensive to simply replace the drive belt first as a trial.
  • Did that work? Do you know which relay to replace? I cannot find the info in the manual.
  • eimaraleimaral Posts: 4
    WWEST, Looks like I've got it fixed. I totally agree with you that the noise is from some bad friction between magnetic clutch and rotor, but I was not sure if is from a bad belt, tortured axils, some dirty stuff stocked in between, or not enough current to produce ample megnetic field so that clutch would not get close enough to the rotor. So, I started with the cheapest try, changing battery......and amazingly, it least for today. I am glad that this is easy and hope it'll be a real problem solver. Will keep you guys posted.
  • relooky01relooky01 Posts: 6
    Look for RR A/C relay in fuse/relay box next to battery in driver's side of engine compartment. The relay next to it labeled HTR is for the front blower motor. If you switch the two the problem should move from the back to the front. The relays pull straight out but are very tight in the socket. You can take the cover off the bad relay and polish the contacts with crocus cloth if you are so inclined. A new one cost me around $20 and only the Toyota dealer had it. Last year I replaced the rear relay with a repaired one and it has worked ever since. Good luck!
  • I'm in Canada, where can I get the part? I asked dealer in canada, was told $123.09+tax, is too expensive, Is there any possibility I can buy from US dealer? don't know if they can ship to Canada. Does anybody have info pls let me know. thanks a lot.
  • I have 95,000 on the Sienna and have not had any major issues. Since last winter, I have a new battery and new belt. Perhaps this is an issue where the belt is incorrect?

    The heat works but when at idle, the air comes out cold. The heat is back instantly as soon as the car is moving. Any ideas on why this is occuring?
  • ateixeiraateixeira Posts: 72,587
    That's so strange I just had to respond.

    Do you have recirc on? Or fresh air?

    I would try toggling that to see if it makes a difference.

    Wonder if some vaccum hoses are loose and the leak prevents certain trap doors from opening in those circumstances?

    I know for the intake a vaccum tube opens a secondary port for more air at high revs.
  • wwestwwest Posts: 10,706
    You have a "vapor lock", air bubble, in the coolant hose to the heater core. Check coolant level.
  • Hello there
    Did you find out what the problem was? I have the same exactly issue and the dealer still saying there is nothing worng. But it is, sometime it heats ok, sometimes is only COLD air and my children are freezen. I got tired and dont know what to do.
  • :mad: On my 2008 Sienna I setup the air to be hot in the front and I also setup to control the rear to be hot. While I am HOT in the front I found out there in only COLD air coming from the rear vents. My kids are freezing and there is no way they can tell me that is COLD because they are 6 months and 1 ½ . I took the car to the dealer at the moment it was happening and even though the guy saw that it was COLD air coming from the rear vents either way he tried , so at the end he told me to set up the AIR to come out from the floor vents , because the vents on the floor were giving HOT air , that way at least my kids won’t get COLD air from the rear VENTS , just while they found an appointment for my car, I had to come back after three days and what happened? They said everything looked fine! There was nothing wrong, that the rear vents are made to only give COLD air. What!!? And he also mentioned that the rear right vent is supposed to give warmer air. What?? I don’t think they are right. I am waiting for this to happen again but I don’t want to go thru this ONE MORE TIME! My kids don’t deserve it! I paid for a NEW CAR to be working OK and so far this looks like a LEMON car because I reported this problem when my car had 300 miles (winter) , now that has 12000 miles (WINTER AGAIN) it is happening again. What do you recommend to do?
  • wwestwwest Posts: 10,706
    edited December 2010
    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.
  • I am also having this exact problem. Can you let me know how you resolved it? Thanks so much.
  • Hello there

    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?
  • yatesjoyatesjo Posts: 186
    edited December 2010
    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.
  • 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
  • nivlenivle Posts: 1
    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.
  • zea3zea3 Posts: 2
    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?
  • 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.

  • wwestwwest Posts: 10,706
    edited February 2011
    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.
  • 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.
  • 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.
  • wwestwwest Posts: 10,706
    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.
  • wwestwwest Posts: 10,706
    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.
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