AC system pressure while compressor isn't operating?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by b0b88, Apr 27, 2020.

  1. b0b88

    b0b88 New Member

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    Hello,

    2011 Prius

    I'll make the story as short as poss, wife bought a prius from used car dealer who promised to repair the not working AC in writing then decided to not answer our calls and duck and dodge us. we have filed a small courts claim and have already gotten an estimate from a toyota dealer who said the compressor needed to be replaced (to start with****). We would like to get at least one other quote from a repair shop for the courts as dealers are obviously the most expensive route. I have called a few places and all of them want to evacuate and recharge the system for a diagnosis/quote if the car isn't already properly charged which is fairly expensive (around 160-200) my question is what should the high and low pressures be if the compressor isn't turning on at all, I'd hate to pay for an evac and recharge if it isn't actually needed. I hooked up a new set of gauges to the car and the High side was 50 PSI and the low side was 35 PSI. from what i've read after many searches the low side being 35 is correct, but i just couldn't find anything about what the high pressure side should be if the compressor isn't kicking on.

    sorry for the longwinded story, just thought some background on why i'm asking would help!

    Thanks for any help.
     
    #1 b0b88, Apr 27, 2020
    Last edited: Apr 27, 2020
  2. b0b88

    b0b88 New Member

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  3. Peter123

    Peter123 Active Member

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    A/C charge is measured by weight. Looking at pressures is not as effective. To do the job right, you have to pump it down to empty and refill it with the correct weight of Freon.
     
  4. 2012 Prius v wagon 3

    2012 Prius v wagon 3 Active Member

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    I don't know specific info about the Pruis AC system, but for AC systems on every other car ...

    If the compressor does not run, the high and low pressures should be the same. It may take some time to equalize to get to this point. So I'll recommend you wait until the compressor has definitely not run (e.g., the car has remained powered off) for a long time (a few minutes should be fine, but longer can't hurt) and re-do the pressure tests. Probably unnecessary, but since I'm very cautious, and I know that I don't know how the Prius AC works, I would actually disconnect the 12V battery before and during the testing. That way you know nothing should be activated, and the pressures should equalize.

    With the AC off, sitting for a while, pressures equalized high-to-low, pressures are dependent on the temperature in the engine bay (specifically the AC system). You should have both liquid and vapor phases of the R-134a in there. As temp rises, some of the liquid will boil off, raising pressure. Your pressure gauge face (needing to look carefully) should have markings on it indicating the temperature based on the pressure.

    Simplified summary:
    - high + low should be the same if the compressor is not running and you took the measurements correctly
    - static pressure readings are temperature dependent

    In addition:
    If you win the case, you'll probably get the diagnosis fee back, just as you'll get your court fees back (assuming you can collect after winning)

    Usually when a compressor fails, it sends debris through the system and other parts need to be replaced. But you don't really know if your compressor has failed like that, which is why you're getting the wiser advice to get a proper diagnosis.

    I'd be surprised if your dealer estimate is challenged. If the defendant does not present anything factual to challenge it, a court would typically accept a professional estimate unless it was outrageous. BTW, this is not legal advice at all. I'm not a lawyer, just a guy who stumbled onto the interwebs.

    Any more details on your Toyota dealer estimate? Like what did they do to come up with that? Did you tell them the AC did not work and they made an estimate based on that, or was it an actual inspection?
     
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