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Toyota Highlander Heating Ventilation and Air Conditioning



  • Probably a straight forward one for you all. I have a 2009 HH - I doubt that it being a hybrid affects this issue. I have the manual heating and air configuration. It's annoying that even with the fan turned to the off position and cabin recirc disabled, I get some mixed air out of where ever the selection knob is pointed. Of course, you can get no air flow in the recirc mode but when the humidity gets high enough in the cabin it automatically goes back to outside air and the air starts coming through again. Is it designed like this - outside mixed air when not in recirc- or is mine broken with a vane that's not closing all the way? We never noticed this in our test drives because it was august and 100f and the A/C was on continuously
  • wwestwwest Posts: 10,706
    First, you probably do not want absolutely no incoming fresh airflow for the same reasons the system will not remain in recirc with the A/C off. The best you can do is place the system in defrost/defog/demist mode and therefore "baffle" the incoming airflow. If you want minimum heating of the incoming airflow then simply place the system in max cold and defrost/defog/demist mode before tuning it off.
  • Thanks for the answer but I must admit I'm a bit baffled by it. The downside of not providing fresh air to the cabin - off really means off - is not apparent to me. Instantaneous fogging of the front window can't be an issue if there is no airflow to get the moisture there. I guess they're trying to protect you against yourself in the event that moisture levels really build up and you turn on defrost/demist. I gather from your answer that the system is designed this way and that mine is operating as designed. I like my Highlander immensly but "the draft" is driving my wife, and therefore me, nuts
  • wwestwwest Posts: 10,706
    Human body metabolism, breathing & perpiration, is a high source of moisture in a closed passenger cabin, 4 passengers = DANGER.

    During the winter months the incoming fresh airflow will typically have a lower Rh than the cabin atmosphere. Have you tried routing the incoming airflow to the footwell. Also, during automatic operation the footwell airflow is often as much as 20F warmer than the airflow you get from the dash outlets.

    Oh, and you can, and should, manually close the leftmost and rightmost dash airflow outlets.
  • tidestertidester Posts: 10,059
    Oh, and you can, and should, manually close the leftmost and rightmost dash airflow outlets.

    Aren't those the ones that are intended to remove moisture from the side windows?

    tidester, host
    SUVs and Smart Shopper
  • wwestwwest Posts: 10,706
    Yes, but primarily only if the A/C is operating. Poster is complaining of the discomfort from natural throughput airflow due to forward motion and these vents can ONLY be closed manually.

    Besides which, I have NEVER expereinced the front side windows being a problem. IMMHO it is ALWAYS the windshield that initially fogs over, begin sto fog over.

    The airflow from any dash outlets can be discomforting during cool or cold weatehr operation so I always try to remember to close these during the wintertime.
  • tidestertidester Posts: 10,059
    I have NEVER expereinced the front side windows being a problem.

    My side windows invariably become a problem when fogging occurs. Fortunately, I live in a dry climate so it doesn't happen very often.

    tidester, host
    SUVs and Smart Shopper
  • wwestwwest Posts: 10,706
    Do you mean in addition to windshield fogging..??

    If not then the airflow from the side vents themselves may be the problem, carrying moist airflow due to the A/C being cycled off as a result of declining OAT or even "exiting" the defrost/defog/demist mode with the A/C otherwise disabled.

    Any time the A/C cycles off there will always be a substantial level of condensate remaining on the ~10,000 square inches of evaporator vane surface area. The only place for that to "go" is to (slowly..?) evaporate into the passenger cabin. Might even be, often is, the next morning before you see the results of yesterday's A/C operation.
  • tidestertidester Posts: 10,059
    Do you mean in addition to windshield fogging..??

    Yes. It was a major problem when we lived back east in a much wetter climate.

    tidester, host
    SUVs and Smart Shopper
  • wwestwwest Posts: 10,706
    Was not only a PITA but downright dangerous here on the "wet" side until I figured out how to "manage" the climate control system. Basically I NEVER allow the A/C to operate for other than actual cooling. Using the c-best options it remains fully off, "disabled" throughout the winter months.
  • Did you ever get the problem resolved? This is exactly my issue.
  • alirobalirob Posts: 17
    I finally sold my 02 Highlander with 104,000 miles (AC problem was never resolved). I replaced it with a new Honda Insight hybrid. So far after 1000 miles it is averaging 41 mpg.
  • tobutobu Posts: 1
    Hey Webgood,

    Thanks a ton for posting here. Thanks to Edmunds and moderators for hosting this great forum. Fixing the nut solved the heating problem ... a great and simple solution save my money.

  • I have 03 Highlander, I was ready to have it fixed but read all the posts. Thanks to all the posts i was able to save my self a lot. Just to add to post # 73, You have to be very careful soldering the tiny connections. Also, to take out the three knob assembly and radio you will need a 10 mm socket.(three bolts on each side) Again,.thanks to all the posts it works great!
  • i have same problem, could you send me instructions on how to remove AC to soder cables?

  • Read post # 73 (kburger1) It has very good explanation on how to take apart.I took a gamble soldering the two boards back together but at that point i had nothing to lose because i'd have to replace it any way. Good luck.
  • I have a 2004 Highlander. Whenever I turn on the heat, it appears that the air conditioner is also coming on. I say 'appears to come on' because the light on the A/C button turns on. I always just press the A/C button and the light goes out. The car heats up okay.

    I'm always wondered about this and my warranty is about to expire so I thought it was time to find out. The service rep at the dealer said he didn't know without seeing how another Highlander operated and I guess he never did check because he never got back to me. We both wondered if maybe it was designed to turn on the A/C to get humidity out of the air. Seems weird though, to have this happen when the weather is below freezing.
  • typesixtypesix Posts: 320
    I also have 2004 Highlander, with manual AC. It will turn on automatically in heat/defrost and defrost modes but the AC light will not light up. It will not turn on automatically in heat or other modes other than mentioned.
  • mikefm58mikefm58 Posts: 2,882
    Scroll back through the posts, common problem with an easy fix.
  • I did search the posts. I did not see anyone reporting the same problem.
  • mikefm58mikefm58 Posts: 2,882
    Is post #61 close to your problem?
  • My 2006 Highlander Limited AC and fan controls stopped working. I called Toyota and was told to have the problem inspected by the dealer. Did that and found the issue as described by everyone here was the problem. Toyota indicated they might cover the cost. Turns out they won't because not enough people have complained to Toyota. If they receive enough customer complaints, then they will pay the cost of replacing the AC Control Head. Call Toyota at 1-800-331-4331. If enough of us let them know about this issue, then we may get it covered by Toyota.
  • I don't think so. Let me provide more detail. My car has climate control, so when I want heat, I press a button marked "Auto". There is also a knob control for selecting the desired temperature. I have this set at 80 or higher in the winter. There is also a button marked "Mode" where I can adjust which vents are being used. There is also a button marked "A/C" and a button marked "Defrost".

    When I press the Auto button and have the temperature set at like 80 or 85, hot air flows from the lower vents. The A/C button lights up, but it is still hot air coming out. I think other people were reporting getting the wrong temperature of air coming out. That is not the problem here. I just wondered if the A/C should be running when the car is not in defrost mode.
  • wwestwwest Posts: 10,706
    Modern automatic climate control systems only turn off the A/C compressor under certain situations. Low refrigerant, OAT below 35F, engine coolant approaching an overheat condition, or WOT, Wide Open Throttle.

    The thinking, horribly FLAWED thinking IMMHO, on this seems to be to use the A/C to help dehumidfy the cabin atmosphere thereby lowering the potential of windshield fogging and at the same time raising the human comfort level. Seems we are more comfortable with an Rh near 40F

    There is a C-best option, 2 actually, that the dealer can set which will allow you to disable the A/C indefinitely by simply turning it off once. The second c-best option unlinks A/C from operating automatically, with no operator indication, in any of the defrost/defog/demist modes.

    My '01 F/awd RX300 has had both of these set for many years now. Prior to those C-best options I always simply unplugged the wire to the A/C clutch during the winter months.
  • pktlosspktloss Posts: 1
    edited May 2010
    For those experiencing the intermittent A/C cooling and heating issue that is very common with the Toyota Highlander you might want to use this source which detailed the problem and fix. Pretty simple fix (aside from the soldering) that can save you a bundle of money. is the short URL.

    If you don't like short URL's here is the original: e/

    Hope others find this useful.
  • mikefm58mikefm58 Posts: 2,882
    Thx for th info. The issue with my HL is getting worse. I have the bolt tightened right down, no play in the knob, and just yesterday I had to jiggle the knob to get the A/C to blow real cold air. Is this the soldering issue?
  • slowcarslowcar Posts: 66
    Passenger's side is barely cold while the driver's side is warm...don't know why? I thought both sides share the same flow volume but why one side is warm, the other barely cold???? it baffled me....
  • rohoorohoo Posts: 2
    My Highlander had the exact same problem and I thought that it was a mixing valve or solonoid of some sort...took it to dealership, they told me that the compressor had a "hole" in it. Solution - new compressor 1,000.00. :mad:

    Just got the Highlander back from dealership - air is cold on both sides now.
  • slowcarslowcar Posts: 66
    Darn...$1K !!! But that did not explained the problem though. I have a technician at independent shop to look at the problem and he said the hi-side pressure was on target; it wasn't like the compressor couldn't "compress" the freon any more....Did they explain exactly what the "hole" was about? Anyway, thanks for the info.
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