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AC Diagnostic

Discussion in 'Gen 2 Prius Main Forum' started by BigBlackBunny, Jul 5, 2022.

  1. BigBlackBunny

    BigBlackBunny Junior Member

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    Over the last 10 years, the AC in my 04 base model prius has been declining in efficiency slowly.

    I got the AC recharged recently. Refrigerant was low, but still had pressure.

    Compressor and low pressure line going into cabin are frosty (AC not blowing hard). I can scrape frost off with a fingernail.

    Occasionally, cold air will blow nicely in the car. This is less than 5% of time that the AC is engaged When it blows, frost on compressor and lines leading into cabin go away. Otherwise, air flow rate is absolutely minimal (and cold), but not nearly what is necessary to keep me from sweating my ball bearings off in the summer heat.

    If the car is sitting in the shade for a while, I may get a few minutes of cold, hard blowing AC.

    First thought is that the evaporator is too gummed up to work more than a short time.

    Second thought is that the driver side fan on the radiator seems to have failed, but I have no idea if this would even be relevant.

    I could be way off. What do you guys think?
     
    #1 BigBlackBunny, Jul 5, 2022
  2. mr_guy_mann

    mr_guy_mann Senior Member

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    Short form, the radiator fans are extremely relevant- both have to work correctly.

    Posted via the PriusChat mobile app.
     
    #2 mr_guy_mann, Jul 5, 2022
    lech auto air conditionin likes this.
  3. ChapmanF

    ChapmanF Senior Member

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    I am thinking even more of the blower inside the dash. The OP reports "not blowing hard", and the usual result of not enough cabin airflow is that not enough cabin heat gets taken up by the refrigerant, so the suction line stays extra cold and develops frost.

    That would move me to look at the cabin filter and cabin blower. The filter wouldn't have the intermittent behavior described here though.

    I think it can also be possible for an incorrect refrigerant charge, dodgy TXV, or possibly evap temp sensor, to lead to overcooling the evaporator. The car will want to control it to down near freezing but not quite, so it doesn't frost up. If the coil builds up frost, that in itself blocks off airflow and makes a vicious cycle that can end up with the coil completely blocked by ice. Then you get an intermittent behavior where it works great when the ice thaws, but then the airflow diminishes as the coil ices up.

    @lech auto air conditionin may have more.
     
    #3 ChapmanF, Jul 5, 2022
    lech auto air conditionin and Tombukt2 like this.
  4. mr_guy_mann

    mr_guy_mann Senior Member

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    Certainly possible. However, if one radiator fan is dead, then there would be no low speed function at all as the fans are switched to series. So possibly some cooling but no condenser airflow at standstill until the high side pressure spikes. Then high speed (parallel) turns on but only 1 fan works...

    Whatever is going on needs to be diagnosed, so the OP needs to have some testing done. Need some pressure gauge and HVAC scan data readings.

    Posted via the PriusChat mobile app.
     
    #4 mr_guy_mann, Jul 6, 2022
    Data Daedalus likes this.
  5. lech auto air conditionin

    lech auto air conditionin Senior Member

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    Could not have said it better myself
     
    #5 lech auto air conditionin, Jul 7, 2022
    Data Daedalus likes this.
  6. BigBlackBunny

    BigBlackBunny Junior Member

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    Just to finish off this thread for the information of anyone searching, even though so much time has passed, the problem was the blower. It got gummed up. I cleaned it, greased it, and it is working wonderfully these days.
     
    #6 BigBlackBunny, Feb 24, 2023
  7. ChapmanF

    ChapmanF Senior Member

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    (y)
     
    #7 ChapmanF, Feb 25, 2023
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