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Air Conditioning: Cold at high speeds & hot when slow

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by LadyBTree, Jul 29, 2015.

  1. LadyBTree

    LadyBTree Junior Member

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    I have a 2006 with 230,000 miles on it. All original parts. I'm having an issue with my AC that has me frustrated. If the weather is around 80 degrees, the AC works fine at any speed, but once the outside temperature goes over 85, if I drive at 50 mph or faster, the AC blows ice-cold air and if I'm driving slowly in traffic, the AC air temp slowly gets warmer and warmer. any ideas?
     
  2. JC91006

    JC91006 Senior Member

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    Maybe you're low on Freon
     
  3. LadyBTree

    LadyBTree Junior Member

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    Nope! That was checked by the dealer and charged along with the possiblity of a leak, but all good.In fact, the dealer gave a price break on the charging.
     
  4. valde3

    valde3 Senior Member

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    Are both fans running when you turn the AC on?
     
  5. JC91006

    JC91006 Senior Member

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    well the dealer should know if it needed a charge. They shouldn't just charge it for no reason.
     
  6. bisco

    bisco cookie crumbler

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    could a weak hv battery cause this?
     
  7. LadyBTree

    LadyBTree Junior Member

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    Not sure. I'll have to check.
     
  8. 69shovlhed

    69shovlhed Surly tree hugger

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    if the dealer did charge it, then there is a leak. no need to charge a full system.

    next time it starts blowing warm, make sure the fans are blowing on high speed.

    just for grins, look at the condenser to make sure its not blocked with leaves or debris.
     
  9. jtuchol

    jtuchol Member

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    I had a 2005 prius with same issues found out the compressor was worn out . one way to test this is start car in driveway turn air on leave run & take a garden hose on run over compressor while running, the compressor is a electric compressor so no belt , after a bit of time doing this go back in car & see if any change in coldness of air if so compressor needs changed out.
     
  10. LadyBTree

    LadyBTree Junior Member

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    What about the idea that it is the AC Amplifier? I'm thinking that if it works well for an extended time period (this whole summer!) at all, I can't be leaking too much freon. My understanding is that the AC Amplifier is the brain that switches the AC from the gas engine to the Electric Motor when the Battery system is in us, as in idle or low speeds. Any thoughts? But I will look at the condenser for debris and I'll try that hose thing too.
     
  11. Eclipse1701d

    Eclipse1701d Prius Enthusiast

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    Another thing to check is that your radiator fans are working properly and your radiator coolant level is correct. If the engine starts to get too hot, the AC will cut out. (This will also happen if there was front end damage and the fans were installed in reverse.) When you are driving at 50MPH the outside air is providing the cooling to the radiator. When you are in traffic, the cooling is dependent on the fans. I think that is your problem, not the A/C itself. Also, you can't depend on the Check Engine Light to tell you this. The A/C will cut out way before the engine temperature is high enough to light up the CEL.

    So, turn on your car and open the hood. Wait for the fans to kick in. If they don't it could be the relay or a sensor that turns the fans on or off. If you has front end work done, and the fans do kick in, and the air is blowing toward you, they put them in in reverse.

    Either way, it sounds like there is something going on with your engine coolant system that is affecting your A/C.
     
    #11 Eclipse1701d, Jul 30, 2015
    Last edited: Jul 30, 2015
    koolingit and valde3 like this.
  12. valde3

    valde3 Senior Member

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    AC is always running on electricity. AC amplifier controls the AC. It’s unlikely that some fault with AC amplifier (except the fan controlling circuit) would cause AC power to be dependent of vehicle speed.
     
  13. LadyBTree

    LadyBTree Junior Member

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    This makes a lot of sense, although I never had front end work done. So I'll check coolant levels and the fans. Thank you
     
  14. Mendel Leisk

    Mendel Leisk Senior Member

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    If it's cooling better at high speeds, maybe the fans aren't working properly? They come into play more at low speeds and/or stopped.
     
  15. 69shovlhed

    69shovlhed Surly tree hugger

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    easy to check the fans. when the car is hot and the a/c is running, open the hood, listen for the fans running and stick your hand behind the fans to feel them blowing.
     
  16. Del Schier

    Del Schier Junior Member

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    Our 147K mi 2006 Prius doesn't have AC when car is sitting hot and battery charge indicates low. It seems to work fine in cooler temps. Gauges read ~30psi low side and 190psi on the high, which according to a gen 3 service document that is about right. The condenser looks clean and the fans are running. When 81 deg outside the ducts are below 40 deg.

    It seems to have something to do with the battery charge level being low and only when hot inside the car. There are no fault codes and the battery modules all read almost exactly the same with diagnostic software reading the OBDII port.