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AC diagnosis...

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by scm2000, Aug 3, 2017.

  1. scm2000

    scm2000 Active Member

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    Hi I have a 2007 Prius 195k miles on it.
    At the beginning of last summer the dealer replaced the AC compressor.

    Now this summer its blowing hot air.

    I bought a set of gauges to try to diagnose the problem.... a lot of it hinges on knowing if the compressor is running.

    The examples on videos and other online sources say just look to see if the clutch is engaged and turning the compressor... of course this does not apply to an electric compressor...

    So how can I tell if the compressor is running... I can't tell by sound since mostly I think I'm only hearing the fan sound.
     
    #1 scm2000, Aug 3, 2017
  2. ChapmanF

    ChapmanF Senior Member

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    You could take a moment to listen to someone else's Prius with a known-working compressor, until you're confident you can tell the sounds apart. The fans sound like fans; the compressor sounds more like a blender, or a distant moped.

    If you have something like a ScanGauge II, or the Torque app on a phone, you might check if the set of known Prius PIDs includes the compressor RPM. I know there is a compressor RPM PID for the Gen 3 Prius. Or if you have Techstream, you can probably see it there.

    -Chap
     
    #2 ChapmanF, Aug 3, 2017
  3. scm2000

    scm2000 Active Member

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    Well... my diagnosis of my ac problem is: Can't tell if compressor is running, I get about 100 on both low and high side... that would be fine if the compressor is not running, and I should be looking for reasons why the compressor wont kick on. If the compressor is running, I read various opinions... bad compressor, bad expansion valve.

    So I brought it to a repair shop asking them to diagnose it. By now I know that their business really is in topping up the charge, and not AC diagnosis, because their diagnosis is: It's full of gas, and there is a trouble code indicating a problem with the passenger side solar sensor.

    Number 1: 2007 Prius has no passenger side solar sensor.. it's on the driver's side.
    Number 2: I read that this is a nuisance code, because if you check for codes in a garage, you get the code. I doubt they rolled the car out to the parking lot in the sun to check codes.

    In any case... Now I have to do my own diagnosis on the solar sensor to rule out a bad sensor or amplifier. My understanding is this sensor only increases or decreases the amount of AC based on sunlight, so not sure why a bad sensor would completely cut out the AC.

    so one question is... How do you get the sensor out of the dash? I've seen others ask this question and they get no answers.
     
    #3 scm2000, Aug 5, 2017
  4. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Don't worry about the solar sensor, that is not the cause of the AC not working. If you get the same pressure reading on the low and high sides, that is proof the compressor is not running.
     
    #4 Patrick Wong, Aug 5, 2017
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  5. edthefox5

    edthefox5 Senior Member

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    The mfd will show ac trouble codes. Seen it here on this site a few times but do not remember how to call them up on the mfd. maybe search it YouTube,

    Any competent ac place can figure it out quick. First they will inject dye and sniff and look for leaks.
    If your still want to see if the compressor is coming on it's pretty easy to tell put the ac on max high cool and the inverter will be screaming if compressor comes on. If quiet the compressor is not coming on.
    Probably pressure switch detecting low charge. Don't home charge it bring it to a car pro.
     
    #5 edthefox5, Aug 6, 2017
  6. Mendel Leisk

    Mendel Leisk Senior Member

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    Considering the dealership replaced the compressor last summer, maybe you can get a gratis check? Or you just don't trust them now?
     
    #6 Mendel Leisk, Aug 6, 2017
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  7. ChapmanF

    ChapmanF Senior Member

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    Hold AUTO and RECIRC while turning the car ON.

    -Chap
     
    #7 ChapmanF, Aug 6, 2017
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  8. edthefox5

    edthefox5 Senior Member

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    Thank you.
     
    #8 edthefox5, Aug 6, 2017
  9. edthefox5

    edthefox5 Senior Member

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    Good one Mendel missed the dealer point.
     
    #9 edthefox5, Aug 6, 2017
  10. ILuvMyPriusToo

    ILuvMyPriusToo Senior Member

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    Check the fuse for the AC compressor. I believe it is position 17 in the instrument panel (under dash) fuse box.
     
    #10 ILuvMyPriusToo, Aug 6, 2017
  11. ChapmanF

    ChapmanF Senior Member

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    The compressor is high voltage, fed by three serious orange wires straight from the inverter box in the engine bay. Any overcurrent protection it has wouldn't be mingled with low voltage fuses under the dash.

    -Chap
     
    #11 ChapmanF, Aug 6, 2017
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  12. ILuvMyPriusToo

    ILuvMyPriusToo Senior Member

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    Excellent point - maybe there are fusible links on those lines?

    There is a 10A fuse in my Gen II instrument panel fuse box labeled A/C (HTR) that I mentioned in my earlier post. Maybe that powers the compressor relay or blower motors? I haven't tried to pull it to see what happens if it is out.
     
    #12 ILuvMyPriusToo, Aug 6, 2017
  13. ChapmanF

    ChapmanF Senior Member

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    The compressor doesn't need a relay; in Gen 2, the three-phase voltage supplying it is under complete control of a circuit in the inverter. It may not need fusible links either (perhaps there are some inside the inverter enclosure, just as a last resort), since it is fed by dedicated, solid-state, current-sensing, regulated circuits in the inverter.

    The 10 amp fuse you found is clearly for the HVAC system in general, not for air conditioning specifically. 10 amps is too small even for the blower circuit. It'll be for the other miscellaneous stuff: the ECU that controls the HVAC, the little servo motors moving the air deflector doors around, relays for the blower, engine-stopped coolant pump, etc.

    As you're probably starting to suspect, the system is complex enough that one wouldn't usually begin diagnosis by guessing about fuses etc., unless there was something preventing the easy first step of asking the HVAC ecu what it thinks might be wrong.

    -Chap
     
    #13 ChapmanF, Aug 6, 2017
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