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A/C Amplifier Location

Discussion in 'Gen 2 Prius Technical Discussion' started by jerlands, Jun 7, 2019.

  1. jerlands

    jerlands Member

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    I was able to test the ac fan and it runs correct. I didn't test the engine fan hower... probably would have been a good idea :) Anyway... does the AC system cause the engine cooling fan to operate or how does that work?
     
  2. ChapmanF

    ChapmanF Senior Member

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    Both fans should always run together. The relays switch the circuit around in a clever way, so both fans either run at low speed (they're electrically in series) or both at high speed (they're in parallel).

    Roughly, they run in low any time the A/C is on, or if the engine needs some cooling, and in high if the engine needs more cooling or the A/C line pressure goes over a threshold.
     
  3. jerlands

    jerlands Member

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    Ok... both my fans do not run at the same time? seems this could be an amplifier problem and wonder if there is a way to do a factory reset on it? I've been under the car while it's running changing coolant and have noticed both fans on?
     
  4. ChapmanF

    ChapmanF Senior Member

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    If both fans don't run at the same time, that's a problem. It could be a wiring problem, a fuse problem, a fan motor problem, or a relay problem. One thing it can't be, if you look at the wiring diagram, is an A/C amplifier problem. The A/C amplifier doesn't have any way to make one fan run without the other one, even if it were messed up and wanted to.
     
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  5. edthefox5

    edthefox5 Senior Member

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    Salved title infers the wiring is messed up to the fan if the car hook a hard front end hit and everything was crushed in.

    Fans run off relays.

    Or maybe the fan is dead. I would jump 12 volts into the fan if you are able to check it. Both fans must be on if ac on.

    The ac ecus I discussed earlier turn those fan relays on and off.
     
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  6. jerlands

    jerlands Member

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    I've run all the active techstream tests and on the "electric fan" I remember it now as simply on/off and not variable but it seems the test only was for one fan and only one speed?
     
    #26 jerlands, Jun 16, 2019
    Last edited: Jun 16, 2019
  7. jerlands

    jerlands Member

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    The fan not running definitely now sounds like a problem so I'll have to check that out but I'm not certain about the "ac ecus" you're talking about?
     
  8. ChapmanF

    ChapmanF Senior Member

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    The A/C amplifier. (One ECU, two wire harness plugs that connect to it.)

    I remember for sure in Gen 1, both the A/C amplifier and the engine ECU got votes on switching the fan relays, and I think one or both of the engine coolant temp switch and the A/C pressure switch had direct representation too. But I haven't looked closely at a Gen 2 diagram to see what might be the same or different.
     
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  9. jerlands

    jerlands Member

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    That sounds like I'm heading somewhere in the right direction :) I'll check the relay first then the fan and harness but I think it ends up at the amplifier right? I'm suspecting the amplifier because of the intermittent steering wheel recirc control?

    Is there a way to factory reset the thing?
     
    #29 jerlands, Jun 16, 2019
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  10. ChapmanF

    ChapmanF Senior Member

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    I t seems to me if you find an actual problem with the amplifier, it might be the first I've ever seen in years of reading PriusChat. Like most car microcontrollers, it's all solid state, no moving parts, just sits there and does its thing, year after year. Unless you're in a flood and drown it.

    Intermittent steering wheel controls very often turn out to result from wear in the spiral cable behind the steering wheel. That thing moves every time you steer, so it can definitely wear out.

    Returning a little to #24, if you've got one fan running and the other not, there are various things that could cause that, but the A/C amplifier isn't one of them—at least not if the engine is up to temp. Looking at the 2006 wiring diagram (pages 346 and 347), the A/C amplifier has two outputs, RF and CF (pins 14 and 15 of connector A8, respectively). It pulls CF low whenever you're using A/C, and it pulls RF low when you're using A/C and it needs more cooling. You might guess CF and RF control two different fans, but no, that's not how the relays and wiring are arranged. When CF is pulled low, the result is both fans run at low speed. Later, pulling RF also low switches both fans to high speed.

    The engine water temp switch is in parallel with the CF output, so when the engine is hot, both fans will run on low, the same effect as CF from the A/C amplifier. That's a straight old-fashioned switch, so that'll happen no matter what any ECU is doing.

    The A/C high pressure switch is in parallel across RF, so if high pressure develops, both fans will switch to high speed. Again, that's a straight, no-nonsense switch, so high pressure should kick both fans to high even if the ECU is out to lunch.

    The ECU for the engine also has an output, FAN (pin 8 of connector E7) that's in parallel with that pressure switch and the A/C RF signal. So if the engine ECU wants to kick both fans to high, it can, regardless of the A/C pressure or what the A/C amplifier wants.

    So you can think of "fans on" (initially at low speed) as the wired-OR of (engine water temp switch, A/C CF output).

    Then, "bump both fans to high" is the wired-OR of (A/C pressure switch, A/C RF output, engine ECU FAN output).

    By design, "fans on" is supposed to happen first, then "bump both fans to high" happens later. But I can see what would happen if somehow "bump both fans to high" happened without "fans on" first. That would be if any of (A/C pressure switch, A/C RF output, or engine ECU FAN output) was pulled low, but without either of (engine water temp switch, A/C CF output). The result would be just one of the fans running (the one with a blue and a white-with-black-stripe wire), but on high speed.

    Other failure modes could cause only the other fan (the one with a green and a white wire) to run, and only on high speed.

    It will take you some legwork to pin down what's going on. Maybe you could start by identifying which fan it is that is running. Also, what happens if you warm up the engine to 95°C or so? Does that change the fans-running situation?

    A multimeter and the wiring diagram are your best tools for something like this. There's a problem in there somewhere, but a lot of things it could be, things more likely to wear out or corrode, further up the suspicion list than an ECU.
     
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  11. jerlands

    jerlands Member

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    I'm confused about the two speeds? on the diagram I don't see any means for this?
     
  12. ChapmanF

    ChapmanF Senior Member

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    Look again at what the SPDT "Fan no. 2 relay" does. In its de-energized state, terminals 3 and 4 connect, and the two fan motors are in series. 12 volts from Fan no. 3 relay, through the "condenser" fan, through no. 2 relay, through the "radiator" fan, to ground. Each fan is seeing about six volts. Low speed.

    You can see that the wired-OR for high speed energizes both Fan no. 1 relay and Fan no. 2 relay, which now connects terminal 3 to 5, not 4. Now both fans are getting the full 12 volts, in parallel; one from No. 3 relay and to ground through No. 2 relay, the other one from No. 1 relay and directly to ground.
     
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  13. jerlands

    jerlands Member

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    I can now see the series path from the 30a CDS Fan Fuse (whatever CDS means), through fan relay 3, the AC fan motor, then through fan relay 2 in the open position to the radiator fan motor then to ground (actual current flow is in the opposite direction :) the path when fan relay 2 is closed changes the current path from fan relay 3 to the AC fan motor then to ground with the full voltage from CDS which would then be high speed? but I still don't see the logic where the amplifier would not prevent the radiator fan from not turning? I think it might just be too late in the evening right now :) I have to look at this again...

    nor however do I understand the logic in the amplifier nor what that other signal going to the control junction box for fan relay 1 and 2 and labeled LG?
     
  14. ChapmanF

    ChapmanF Senior Member

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    Going in reverse order:

    I don't have that open any more, but isn't that the one that just crosses to the next page and the FAN output of the engine ECU?

    I'm not sure I can untangle all of the 'not's in that.

    Oh, a wise guy, eh? :)

    Sure, in metal wires, current flow is by movement of electrons, but at the same time, in comparing the charges on protons and electrons, the (arbitrary) decision to call electrons the negative ones got made long ago. So positive current flow is in the direction the electrons are not moving.

    And there are other situations, like in battery electrolytes, where the charge carriers are positive ions, so they're moving in the same direction as the nominal current flow. In circuits that have both wires and batteries (like this one!), if you wanted to always say current 'flow' was in the direction the charge carriers were moving regardless of whether they carried positive or negative charge, you'd have your arrows bonking into each other.
     
  15. jerlands

    jerlands Member

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    Yes, it comes from the ECUs output labeled "Fan".

    I can understand that :) Anyway... I have...
    Radiator Fan = ECU or Pressure Switch (I'm assuming AC?) or the Amplifier and all of these signals also change the path from fan relay 2 so that the fans run on high speed.
    AC Fan = water temp switch or the Amplifier...
    My confusion was in understanding when I should see both fans operating and I understand now that I won't see both fans running when I first start up the car with the AC on until the engine temp comes up. However, I still don't understand how the fans could operate properly with an amplifier that might be fritzy? and along those lines I'm not sure of the conditions that have to be met for the amplifier or the ECU to signal some change in state of the fans? That might indicate some sensor failing?


    I had the idea electrons were assigned a negative charge because the protons seemed to attract electrons?
    coulomb's law :) and I understand that on charging in a battery the current flow is from positive to negative through the electrolyte (I think :)
     
  16. Skibob

    Skibob Senior Member

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    Perhaps I’m stupid but if both fans are wired to go on at the same time but only one goes on it’s either the non working fan or the wiring. Stop making it so complicated. Check the fan and see if you have power to the non working fan.
     
  17. Skibob

    Skibob Senior Member

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    With this series/parallel thing could something like the ac amplifier detect this and turn the AC off? Like the fans can’t work in series because of the bad fan, but the good fan can work in parallel?
     
  18. ChapmanF

    ChapmanF Senior Member

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    Well, in a car where everything works right, you will see both fans running when you first start up the car with the AC on, regardless of engine temp. The A/C amplifier is responsible for asserting CF whenever A/C is turned on, and CF (if the fuses/wiring/relays/fans are all ok) causes both fans to spin at low speed. As would the water temp switch. They are wired together as an OR, so either one will have that effect.

    You will probably make more progress approaching it from the other direction. You know the system is designed to never have one fan running without the other. Its only design operating conditions are both fans low, or both fans high. If you are seeing one fan without the other, you have a diagnosis task in front of you. Instead of deciding the A/C amplifier is the culprit a priori and then asking yourself how could a fritzy amplifier cause this?, I recommend asking what is causing this?, using your meter and observational skills to find out, and then you'll know if the cause is the amplifier or something else. As a statistical-variety hint, it's more likely to be something else.

    Well, electrons attract protons too. Wouldn't that mean the protons should have been called negative? :) It was an arbitrary choice. Somebody made it, and there it is.

    This is one of those areas where the definitions were all chosen in a way that is nice and consistent if you just step back and let yourself use algebra, rather than distracting yourself with what particular tiny particles might be doing. A "current flow" is just defined as the direction positive charges would be moving. In a substance where the actual mobile charge carriers are negative, they happen to be moving the other way, but that doesn't change how the "current flow" is defined.

    Now, if you design semiconductors for a living or something, then yes, you have to care what the particles are doing.

    Well, it's a smidge more complicated—there are relays and fuses in there—but yeah, that's the idea,

    What is the sound of one fan in parallel? :)

    I don't think the system has any direct monitoring of the fans. It will tell you if the coolant overheats, and stop the A/C if the pressure goes too high. Short of that, you'll just have cooling less effective than you expect.
     
  19. Skibob

    Skibob Senior Member

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    And perhaps the R134A is getting overheated because only 1 fan is working? The OP is convinced it’s the AC amplifier when he has a known broken part in front of him. A cheap and easy to replace part no less. I wonder if he’s a college professor?
     
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  20. ChapmanF

    ChapmanF Senior Member

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    In the life of a college professor, there might be a need now and then to help some student see how to sort through the evidence before jumping to a conclusion, so a professor had better be at least able to pretend to be doing that. :)

    The conclusion is not quite ready to be jumped to yet. There are a few relays, a couple fuses, two fan motors, assorted connectors and/or wiring (mouse damage?), all still in the lineup waiting to be eliminated.

    A person who wanted to get to the bottom of the problem would be out there with a multimeter and the diagram making the tests that would eliminate some of those candidates.
     
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