Ever worsening a/c problem

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Jon Batchelor, Jun 27, 2025 at 2:34 PM.

  1. Jon Batchelor

    Jon Batchelor New Member

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    I've had a problem with my A/C that has been getting worse for the last two or three years. I've asked the dealership to look into it 3 or 4 times, but either they never have, or they never found anything. Up until now the problem has been minor enough to ignore, but it's getting to the point where I can no longer ignore it. So I thought I'd explain what has been happening, and see if someone says, "I've seen that exact problem before, it's something detailed.

    Started a few years ago. I noticed that much of the time if I had my A/C set on a low blower strength, it would barely blow at all, though it used to. At first it was if it were on spots one or two, it wouldn't really blow, but as soon as I moved it to 3, it would start blowing. Then it had to be four or five before it would start actually blowing ... though if it wasn't really needed, I'd just keep driving, then it would randomly decide to start blowing more powerfully.

    Went out driving passengers today, and it's a hot Florida summer day, and the temperature was getting higher and higher, and I was cranking the A/C higher and higher, and it wasn't doing anything. I finally got it cranked up to max (7), and it still wasn't blowing. While the dash still claimed the inside of the cabin was 72 degrees, it was getting hotter and hotter inside. It got to the point that customers were starting to complain, and I finally had to stop accepting new calls.

    By this time the A/C had been on max, but hadn't been blowing at all for maybe 40 or 50 minutes, and then it finally turned on and started blowing lots of air, and didn't give me any more problems for the rest of the day, but for an entire hour or two it hadn't been doing anything, when it should have been. Any fairly confident ideas of a possible problem?

    Myself, I find myself beginning to wonder if maybe there's a thermostat somewhere that's somehow 'sticking' worse and worse and worse over time?
     
    #1 Jon Batchelor, Jun 27, 2025 at 2:34 PM
  2. Jon Batchelor

    Jon Batchelor New Member

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    More than a day and this still hasn't even been approved to be shown to people. Obviously I am wasting my time here.
     
    #2 Jon Batchelor, Jun 28, 2025 at 7:52 PM
  3. Grit

    Grit Senior Member

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    If you thermo was stuck, you’d have bigger problems. Shocked you haven’t had the ac and refridgerant lines looked into yet.
     
    #3 Grit, Jun 29, 2025 at 4:12 AM
  4. Brian1954

    Brian1954 Senior Member

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    When was the last time the cabin air filter was replaced?
     
    #4 Brian1954, Jun 29, 2025 at 8:55 AM
  5. ChapmanF

    ChapmanF Senior Member

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    Everything you've described here is making me think of a simple intermittent problem with the blower motor, and not of anything else.

    If you're of a measure-twice-cut-once mindset, you could hang a voltmeter on the power wires to the blower motor and make sure it isn't a matter of the power cutting out. If the power is holding steady and still the blower sometimes-blows-sometimes-not, that's probably a good enough sign to look at the blower motor.

    There is a signal the A/C amplifier sends to the blower motor telling it how hard to blow. That signal is hard to check without an oscilloscope, though, so if you don't already have one of those, it's cheaper just to try swapping the motor than to buy a 'scope.

    Gen 3 was available with and without a solar roof, which was used to run the blower and keep the unattended cabin cool on hot days. Because of all the extra run time, they put a brushless blower motor in that trim. All the others without the solar roof got a conventional motor with brushes that wear out. If you're a very frugal sort, sometimes you can open the motor and clean a bunch of carbon brush dust off the commutator, maybe find new brushes for it, and get it going again.

    The motor shouldn't be much money at a salvage yard.

    There isn't any built-in dash display that shows you what the inside of the cabin is. The bigger numerals on the left show what you've set for what you want it to be, and in smaller ones on the right is what the outside temperature is.

    The A/C amplifier does know what the cabin temperature is and you can view that number if you have an add-on display that plugs into the on-board diagnostic port. But the factory display doesn't show it.
     
    #5 ChapmanF, Jun 29, 2025 at 9:18 AM
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