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Toyota Highlander Heating Ventilation and Air Conditioning



  • wwestwwest Posts: 10,706
    Too much refrigerant and the pressure switch that activates the compressor is always open, especially if the OAT is HIGH.
  • jannersjanners Posts: 1
    It is definitely the nut behind the control knob. i believe htis is a fault with Highlanders. It comes loose and finally the wires break behind the knob making the heat either full on or intermitent.
    I tried to solder the wires but in the end bought a replacement unit on ebay for $200. the dealer wanted $700 to do it and $565 just for the part. it is easy just pry out the facia and then undo 4 screws the whole thing pops out and then replace with new or used unit.
    If you are good at soldering it could save you a lot of money. If it has only just happened you may be lucky and get away with tightening the nut behind the control knob

    Good luck!
  • karen42karen42 Posts: 2
    I took the temp control knob off and the nut was loose just like you all said,so I tightened it. It helped with the cool/warm air blowing when I just used the vent,. but my A/C still blows warm air when I turn it on. I'm afraid I'm going to have to find a repair shop to check it out. I will not go to the dealer since I don't really trust them not to rip me off. Thanks for all the suggestions.
  • ojnucciojnucci Posts: 3

    Could you tell me which part it was you bought on ebay? I would like to do the same thing- my Highlander has been doing this for about 2 years so I've been just half-turning the temp control knob to get cold (though it has still been very intermittent!). Its been a huge thorn and I've been quoted from two separate shops at over a grand to replace the "Blender Box."

  • ggartnerggartner Posts: 3
    Janners: the "Blender Box" is probably what I bought. It has been a while, but I took the module that the knobs hooked into to a junk yard. They found the replacement part - the first one they found, did not work when I installed. They searched other locations around the state and found another one. The second one worked like a champ. I think I paid about $125 for the part finally.
    Sorry this is not more help.
  • ojnucciojnucci Posts: 3
    This helps a lot actually. I have just started the online junk yard scavenging today. However, after tightening the bolt behind the temp control knob it works much better--so I may give it a few months!
    Thanks Gary.
  • kburger1kburger1 Posts: 2
    thanks for pointing me to the loose nut behind the temperature control knob. as thanks here is further info. If you tighten the nut and it still doesnt work try taking the nut off completely and gently move the knob to different positions with the blower on max air. If it changes from hot to cold in different positions the 3 wires connecting that control switch to the next upstream board are severed (broken solder joints) you can remove the whole assembly with the radio first disconnect the positive terminal of the battery. the trim around the radio and ac controls just pulls straight out from the bottom and then at the top very easy. disconnect the wires they are keyed, large connectors goto the air controls, small connectors to the radio. you need to resolder the wires back onto the control knob board. I have been soldering along time and it was hard. good idea to test joints with a multimeter. if you short any of them it probably wont work. you will show continuity between wires even when its done correctly, 2 have full continuity and you also have 1 with a resistance of like .7 which i think is an inline resistor. i replaced the existing grey flate wire with 3 small guage individual wires. label it so you dont get any wires crossed. I just got done test driving the car and the ac and heat work perfect. I hope this helps people out there to fix these problems without paying thousand of dollars to the dealer. I just fixed mine for free. Very satisfying.
  • rutrut Posts: 5
    In my 2002 highlander the air temp will vary with the slightest of bumps. It will jump from hot to cold immediately.

    The dealership wants $800 to replace the panel:( I'm thinking it is a loose wire or something.

    Anyone else seen this problem?

  • mikefm58mikefm58 Posts: 2,882
    Start reading posts backwards. Your answer is in there.
  • wwestwwest Posts: 10,706
    "...slightest of bumps.."

    Most likely a loose/intermittent connection to the OAT, Outside Air Temperature, sensor mounted behind or on the back of the front bumper just forward of the AC condensor/radiator stack.

    And open connection will indicate a sub-freezing OAT and the AC compressor will be disabled and the system will go into heating mode as long as the sensor is open.

    Another "bump", connection closes, AC cooling returns.
  • slowcarslowcar Posts: 66
    Problem description: in a hot day, the aircond only blows out cold air in the passenger side vents, warm air still in the driver side vents. The aircond was put in the recirculation mode; never have from the outside. My thought was that there was some thing (a valve, maybe?) blocking the cold air from going to driver side.

    What's wrong?


    Thanks all for help.
  • leean21leean21 Posts: 1
    ok, let me try this again, without hitting the enter button before i put a message....anyways, I just recently started having the problem of hot air blowing through while my ac is on, then switching back to cold air....i have tightened the nut behind the temp switch and am hoping that is the fix....thanks so much for all the guys are awesome
  • rutrut Posts: 5
    I actually took it apart and found a broken wire connecting the temp knob to the ckt board. It was a 3 wire cable soldered on each end. I removed the cable and replaced it with 3 individual wires. Problem solved.
  • I have same problem and tightened the knob. This has reduce problems but once in a while still get switch from cool to heat. How do I fix the broken cables? are there any specific instructions on how to do this?
  • I have same problem and tightening knot did not fix it. I like to try to solder wires. Could you please send me more specific instructions on how to remove ac unit? thanks.
  • rutrut Posts: 5
    You have to remove the complete unit out. it just kinda snaps out if I remember correctly. there is a circuit board that you have to remove. There are a few screws holding it in. Be careful handling the board as to not emit any static electricity that would take out the ic's on the board.

    You will find a small circuit board mounted where the temp control is. Go assuming you have taken the knobs off in front and removed the nuts on the controls, you can unclip the board and pull it out. There is a 3 wire cable connecting the circuit board to the temp switch. Mine had a broken wire at the small board. Be very careful trying to solder this back. It requires a small tip and not too much heat.

    Hope this helps. Better than spending $800 for a new one or $300 for a used one.

  • alirobalirob Posts: 17
    Slowcar, I have exactly the same problem on my 02 Highlander. Have you found a solution yet?
  • slowcarslowcar Posts: 66
    No...It seems like you and I were the only ones having this problem. It must be some thing very simple that prevents the freon from going to the driver side's vent. Hate to bring it in the dealer and spend $thousands$ .... Please post it here if you found some thing. Thanks.
  • rohoorohoo Posts: 2
    I have the exact same problem on my 01' Highlander. The temperature range is approximately 12-18 degrees warmer on the drivers side as opposed to the passenger side. I will let you know if I come up with anything.
  • Just wanted to thank the original poster regarding the ac temp issue and the loose nut. Just as you said, my husband took the knob off and the nut was loose. Boy am I glad I was reading this yesterday. It saved us a lot of money!
  • slowcarslowcar Posts: 66
    Any news? Also I noticed that the driver's side air will kick in cold if the outside temperature is low enough, like in the low 80's. I even heard a "click" sound from a solenoid when it started getting cold. Of course the passenger's side stays cold the whole time.....Any body's having an idea? Please help.
  • wwestwwest Posts: 10,706
    Thiis is just/simply a guess. In the conditions you describe the Toyota and Lexus series automatic climate control has always, since at least 1990, been VERY prone to sudden, inadvertent, fogging of the interior windshield surface. There is even addressed, obliquely, within your owners manual with a direction to NEVER have the system in defrost/defog/demist mode during cooling airflow operation.

    While those systems are prone to "automatically" putting the system into a mode wherein the danger is more likely to arise, having the manual system in recirculate mode during cooling use is one of the base criteria for "stumbling" across the same windshield fogging situation.

    Even without the system being in defrost/defog/demist mode there is still a not insignificant possibility that the windshield interior surface will be cooled to the cabin dewpoint and gradually, or in some unique case, SUDDENLY fog over with a light coating of condensation.

    What you may be experiencing is Toyota/Lexus latest FIX for the HAZARDS arising from a seriously flawed A/C design. Having the driver's side air outflow be somewhat higher in temperature would undoubtedly allviate some of the potential for windshield fogging on that side of the vehicle.
  • yes, my heat does not stay on "hot" The dealer says it is vacuumed sealed
    and it needs to be replaced for $1000.00. you can pull the knob off and adjust
    the nut. however I have hit bumps in the road and it turns to cold air. I called
    Toyota and they will not recall it due to it is not a "saftey problem" It is when I
    am unable to defrost my windsheild. I am not paying that... more calls to Toyota
    to help them recall this issue.
  • slowcarslowcar Posts: 66
    Thanks, wwest for the information but I don't think that was the problem. The air cond had been working just fine all these years and the problem just popped up more than a year ago. I don't think the temp in driver side is higher than that of the passenger's just that the driver side vent sucks in the carbin's air (recirculation mode) and blows it right back out without having the liquid freon going thru the evaporator. When I heard a little "click" sound of the solenoid then the driver side started getting cold just like the other side. Anyway, thanks for the info. If you can think of any thing else, please advise.
  • wwestwwest Posts: 10,706
    The mechanical airflow path of automotive A/C.

    Air inlet with a damper door to select fresh intake airflow or recirculate. Fresh airflow is usually taken in at the foot of the windshield on the passenger side (US). Recirculate airflow is taken in from an opening behind the glove box' traditional position. ALL system airflow, regardless of fresh/recirc intake origin, then flows through the pollen filter, the blower ("sucker") and then to, through, the cooling evaporator core. The cooling evaporator core is typically operated at ~34F(***). So if the blower speed is fairly low the airflow temperature at this point might be very close to freezing.

    The next step is the reheat/remix vane/door. The control system will "set" the position of the vane door such that a selected portion of that just previously cooled airflow will be diverted from the "main" flow path and through the ~180F heater core. Downstream of the heater core the two airflow portions will remix/merge and the end result will be system outlet airflow that is cool enough, sometimes just BARELY cool enough, to maintain the passenger cabin, OVERALL, at your selected temperature setpoint.

    If you turn the manual control to maximum cooling or the automatic one to the lowest temperature setting then NO airflow will be reheated and the outflow might be discomfortingly COLD.

    *** Currently no method is used to moderate the operating temperature of the evaporator, mostly in order to take full (but RANDOM) advantage of the evaporator's dehumidification aspects.
  • slowcarslowcar Posts: 66
    wwest: few questions.

    1) It doesn't seem to be efficient to heat up part of the cold air (+34F) with the +180F heater core and then re-mix it with the original cold air to regulate the temperature. It's like running your house aircond at full speed and then open the windows slightly to maintain the set temperture.

    p.s. BTW, I thought the car air cond regulates the temperature via the Expansion Valve, where it opens to allow liquid freon from the Condenser to flow to the Evaporator if it wants to cool down the air. When the cabin's air is cool enough this Expansion Valve will be closed; thus no more cooling. Am I wrong?

    2) Is there a vane door separately for passenger side and driver side so that on the driver side, the vane door was stuck and won't allow the cold air to go through and mix in with the warm air? If there isn't a separate vane door for the driver side, then why the passenger side's temp is much lower (20F) than that of driver side if both sides share the same vane door?

    The kicker is that the system had been working no problem until recently !!! So it can't be the problem with the Toyota aircond design.
  • ryan99ryan99 Posts: 46
    Whoever found this quick fix is a genius! I've had my Highlander for three weeks and today found the heat to be erratic. I took the knob off and sure enough the switch was loose and I could duplicate the problem in my hands...Thanks again!
  • I am having the same problem with my 2004 highlander. The temp setting is stuck on 75 degrees. I have pulled out the circuit board and the 3 wire cable connecting the circuit board to the temp switch is not broken. I think I will have to replace the circuit board; however, I have not been able to locate one. Does anyone have any other suggestions as to what might be wrong & how I can correct the problem?
  • wwestwwest Posts: 10,706
    1. Yes, HORRIBLY inefficient these days when public focus is, should be, on FE. But you don't get the full benefits of dehumidification on a humid summer day unless the A/C evaporator operates at the lowest possible temperature.

    All I know, or think I know, is that the temperature of the evaporator vane surface area is not easily moderated. So we get downstream "moderation" via the remix/reheat vane/door setting.

    2. These days, even if you did not purchase a climate control with the L/R different temperature settings the "core" system may still have that capability for purposes of parts commonalty. Then the question becomes is the function being used..? It would make sense to if the radiation sensor indicates the solar radiation heating effects are primarily on the passenger's side then more cooling would/might be routed to that side. A L/R system malfunction is also a possibility.

    To extend FE I often run my climate control systems on MAX COOLING and recirculate. Then I use the blower speed to regulate the overall cabin temperature. If that still results in too much cooling to my face and upper body I set the outlet airflow to dash/footwell combined or footwell only.

    That being said....

    Climate control systems designed by Denso US, NipponDenso, have shown an unusual propensity for sudden spontaneous fogging of the interior surface of the windshield. So running the driver's side outlet airflow a bit higher than the passenger side might well be something of a corrective measure to help alleviate these instances.
  • Anyone have any answers to my question above?
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