Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!

Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!

Did you get a great deal? Let us know in the Values & Prices Paid section!
Meet your fellow owners in our Owners Clubs

Toyota Sienna Heating / Cooling



  • Hi guys,

    I am 2005 Toyota Sienna owner. I have very low mileage less than 10,000 mile on this van. This summer, I had the front fan die on me. The fan will not turn on. The rear fan works without problem. Since it was just over 3 years old, I did not want to pay for the cost of fixing the AC fan or Heater fan problem. Today Dec 22, 2009, I finally spend an hour trying to figure out the problem. Guess what? The stupid heater relay! Since it had two of the same relays, I switched the relay to see which one was defective, Guess what? The front fan will work now. The back will not.

    I looked at the part number; it is a Denso part, made in Tennessee.

    Who should I blame on the failure? This relay should not break. I am so disappointed, I am seriously will think twice next time when I purchase a new car next time.

    Knowing where it is made seems to matter a lot. I am buying a piece of garbage made in USA from Toyota!

    Toyota! you better get your act together, the next time it happen, you will have 1 less customer!
  • Since the AC or the Heater fan relay cause so many people problems. This is a defects in material workmanship and quality control issue in Toyota USA. Toyota is hiring idiots doing their testing and adjustment of the electro mechanical relay. They need to fire that person running the Denso parts plant in Tennessee.

    They need to do that SOON before the Toyota name and reputation go down the drain like you know what happen to GM and Chrysler.
  • ateixeiraateixeira Posts: 72,587
    It's still the most reliable van out there.

    Even if it is bad, it's less bad than any competitor.
  • I recently purchased a 2010 Sienna LE AWD. It has the manual climate control and interestingly enough, you cannot control the rear cabin temperature from the controls on the dash.

    You actually have to reach over your shoulder and make an adjustment on the temperature control located above the left sliding door!!

    My thought is, can I replace that controller with a digital controller from an XLE and it function correctly? Can I replace the one up front with a digital one as well?

    It comes down to if the Sienna's all use a common wiring harness with certain wires unused on the lower end models.

    Anyone with intimate knowledge of this system please chime in!

    Thank you.
  • My 2001 Sienna has 130k miles on it, and everything is fine. In past decades, common wisdom dictated changing water hoses every four years or so, and obviously, I've doubled that, and put a bunch of miles on to boot. I've had people tell me modern hose compounds make them last much longer, but I remain skeptical and am wondering if I should preemptively change them all out.

    Any Toyota techs have advice?
  • wwestwwest Posts: 10,706
    "...common wisdom dictated.."

    No doubt "common wisdom" widely dispersed mostly by dealer service personnel/managers....
  • crodycrody Posts: 6
    The van is 2007 Sienna CE bought new in 2007. Never see condensation water on the garage floor after using AC . I can always see a puddle of water under a 2005 Camry after using AC. By the way, the van's AC is not very cold.
    Can you see condensation water under your Sienna after using AC? Thanks.
  • Get a digital thermometer and check you AC temperature. Sitting still it should be in the 40's moving down the road will be about 40 degrees. Check on the dash vents. Likely you will find it 60 degrees or better. Low freon results in no condensation. With the numbers in hand your mechanic will have a better chance of solving your problem.
  • wwestwwest Posts: 10,706

    Only on max heating and low blower speed when reheat/remix plenum internal airflow path is not active.

    Most newer systems, certainly automatic climate controls, once the cabin is cooled to within a fairly narrow range of "setpoint", avoid discomforting the front passengers with outlet airflow that is TOO cold and dry.
  • Here in Minnesota having heat is a good thing. I noticed this weekend that when I am sitting and idling the heater in the front does not blow warm air. As soon as I start moving, the air temperature coming out of the vents gets nice and warm.

    This weekend I was sitting long enough that the engine temp guage climed well above the mid-point, (waiting for teenage daughter who was just going to be a "minute") so I know that the coolant was more than warm enough.

    I often have the controls set to recirculate and am not sure if the same problem occurs when not in recirculate mode.

    Since I get warm air once the van starts moving, I am assuming that the heater core isn't plugged and that the valve to the core must be open (or are those bad assumptions?)

    This is a 2005 Sienna with 113k miles. Electronic dual controls from heat/cooling.

    Any ideas?
  • 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?
Sign In or Register to comment.