Automatic Climate Control problems

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Jim Biggs, Dec 4, 2006.

  1. Jim Biggs

    Jim Biggs Junior Member

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    2005 Prius; Package 7; 85,000 miles; To date gas mileage: about 50MPG.

    I live in Phoenix so this might be hard for the Phoenix Toyota dealership to troubleshoot.
    Any suggestions would be appreciated.

    Round Trip from Phoenix to Salt Lake City and back
    Outside Temperature range: 16 degrees F to 40 degrees F

    Heat Mode:
    1. When going up hill and engine is working hard, temperature of air from ducts drops noticeably.
    2. When going down hill and engine is spinning, temperature of air from ducts increases noticeably.
    3. On the return trip the following was observed:
    a. For the same outside temperature, the inside temperature command had to be changed from 77 degrees F to 70 degrees F and finally turned off to keep cabin temperature from overheating.
    b. A single non-repeated set of events with the front windshield defroster:
    i. Turning ON caused the display of ducts currently utilized to indicate none selected. Manually trying to select a duct had no effect.
    ii. Turning OFF caused the display of ducts to indicate the defrost setting. Manually selecting a duct worked.
    iii. Turning OFF the entire system and back on had no effect
    iv. Turing OFF the car for the time necessary to fill the gas tank had no effect.
    v. Turning OFF the car for the time necessary to eat dinner (about 40 minutes) caused the defrost system to act normal again.

    Thanks,
    Jim
     
  2. eagle33199

    eagle33199 Platinum Member

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    Those are some pretty odd symptoms... I would guess that, when going up hill, less energy was available for running the heater, and the opposite was true going down hill.

    For the internal temperature change... was the A/C button lit? if the A/C isn't on, i believe the car can't cool the air at all, which may be needed. Also, what time were you having this problem? In my recent road trip (minnesota to ohio and back), we noticed that the car felt a lot colder in the evening than it did during the day. The main reason for this was that we had the sun shining down on us during the day, which makes the cabin feel a lot hotter than it really is, and with it gone at night we had to turn up the heat.

    For the non-repeatable events with the defroster... Very odd, and i've got no advice save this: if it's non-repeatable, it's probably not much to worry about :lol:
     
  3. seasalsa

    seasalsa Active Member

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    <div class='quotetop'>QUOTE(Jim Biggs @ Dec 4 2006, 08:52 AM) [snapback]357409[/snapback]</div>
    Next time try AC/Auto.
    As TonyPSchaefer says,"Just like the variable transmission, you can think of the A/C as a variable system. Basically, if allowed to do it's thing without human interference, it will work extremely efficiently."
     
  4. IsrAmeriPrius

    IsrAmeriPrius Progressive Member

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    I had a similar problem with an older Mercedes Benz. It was caused by leaks in the vacuum system that operated the opening and closing of the climate control system's duct doors. I do not know how those are operated on the Prius, though.
     
  5. Jim Biggs

    Jim Biggs Junior Member

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    I tried it with the A/C both ON and OFF. Very little difference except for fan speed.
    I am leaning towards vacuum leaks. When the engine is working hard, the engine is producing very little vacuum. Going down hill, maximum vacuum (I think).
    Jim

    <div class='quotetop'>QUOTE(eagle33199 @ Dec 4 2006, 10:02 AM) [snapback]357414[/snapback]</div>
     
  6. galaxee

    galaxee mostly benevolent

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    the system uses servo motors to open and close ducts.

    that is unusual. were you using the steering wheel control for the defrost? or the MFD? were you using the auto a/c?
     
  7. Jim Biggs

    Jim Biggs Junior Member

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    Wow servo motors! I just assumed vacuum. When Vivien was driving I operated the defrost from the MFD. When I drove I operated it from the steering wheel. When it screwed up, I was using the MFD.
    Jim

    <div class='quotetop'>QUOTE(galaxee @ Dec 4 2006, 07:18 PM) [snapback]357733[/snapback]</div>
     
  8. seasalsa

    seasalsa Active Member

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    <div class='quotetop'>QUOTE(Jim Biggs @ Dec 4 2006, 06:10 PM) [snapback]357727[/snapback]</div>
    A/C on or off is not AUTO A/C. Let the car do the work. If allowed to do it's thing without human interference, it will work extremely efficiently."
     
  9. Jim Biggs

    Jim Biggs Junior Member

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    So what is the source of power for the servo motors? 12VDC or HV? Could we have a power fluxuation issue?
    <div class='quotetop'>QUOTE(galaxee @ Dec 4 2006, 07:18 PM) [snapback]357733[/snapback]</div>
     
  10. galaxee

    galaxee mostly benevolent

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    it's 12v- HV only runs the electric motors and the a/c compressor. if there was a power fluctuation issue you'd see all sorts of crazy stuff going on.
     
  11. Jim Biggs

    Jim Biggs Junior Member

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    Trust me. I bought this car new. I leave it in AUTO A/C most of the time. It does not do anything very well with the climate control at this time...

    <div class='quotetop'>QUOTE(seasalsa @ Dec 4 2006, 07:24 PM) [snapback]357739[/snapback]</div>

    <div class='quotetop'>QUOTE(galaxee @ Dec 4 2006, 07:44 PM) [snapback]357750[/snapback]</div>
    What controls the water valve?
    Thanks,
     
  12. BVISAILMAN

    BVISAILMAN Junior Member

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    The A/C heating system will work at maintaing your set temperature ONLY if you have the A/C Auto button selected. This is the best position to maintain th etemperature the best.
     
  13. Jim Biggs

    Jim Biggs Junior Member

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    <div class='quotetop'>QUOTE(BVISAILMAN @ Dec 7 2006, 06:46 AM) [snapback]358809[/snapback]</div>
    That is the way I normally keep it. It doesn't work properly at this time.
     
  14. Jim Biggs

    Jim Biggs Junior Member

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    Data is always useful so I present the following:
    Date and Time Command Temp Outside Temp Inside Temp Upper Duct Temp
    12/07/06 Early Afternoon: 75 80 85 65
    12/07/06 Early Evening: 75 65 83 86

    In both situations the Full AUTO, Fan speed indicates one setting faster than low, ducts indicate far left display

    PLEASE can someone point me in the direction of a good technical description of the logic that drives this control system. I need to know as a minimum the following:
    1. What determines the fan speed for each setting
    2. What determines which set of ducts is in use for each setting
    3. What determines the duct temperature
    4. Where are all of the temperature sensors located
    5. Is there a diagnostic mode I can enter and view the various controlling parameters

    Thanks,
    Jim
     
  15. Bob64

    Bob64 Sapphire of the Blue Sky

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    Edit: oh
    Wth
    , I didn't see that this was an old thread until after I posted.


    I think the system takes into consideration:
    Outdoor air temp, interior temp, engine coolant temp, target temp

    I think (may not be accurate - just a guess) the logic is something like this:

    If target temp is lower then outdoor air temp, then turn on air conditioning compressor (strength of air conditioning is based on the difference between target temp and interior temp).
    If target temp is lower then interior air temp and higher then outdoor temp, then a/c remains off.

    If target temp is greater then outdoor temp and its lower then engine coolant temp, then the engine coolant is used to warm the interior.

    If target temp is greater then outdoor temp and higher then engine coolant temp then engine stays on and both electricity and coolant is fed into the cabin to make heat.

    Fan speed is based on difference between interior temp and target temp.
    If target temp is 2 degrees above or below the indoor temp, fan speed is increased for every 2 degrees it is above or below.
     
  16. rwernst

    rwernst Junior Member

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    Not on my 2005. Maintaining temp works fine with it off, ASSUMING outside air temp is opposite what you want inside. (cooler outside than desired inside, or hotter outside than in. If you need cooling beyond the outside temp, you WILL need the AC.
     
  17. dolj

    dolj Senior Member

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    I did notice this was a thread just over 10 yo.

    I'd like to point out that while what you say is true, it does not invalidate the points Bob64 said, as this hypothesis has been establish as the way it works.

    That being said, why bother with the hassle of deciding whether to have the A/C on or off. Just set the thing to AUTO and set the desired temp and let the system work it out? You will find that adjustments are required to the temp (as a persons perception to hot/cold is subjective taking into consideration the outside weather and the clothes you're wearing) and this is easily accomplished by a quick adjustment of the steering wheel buttons – 0.5 deg up or down. KISS.
     
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