AC only cold when driving, radiator fans never go on high speed

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Krokettenslayer, Aug 8, 2020.

  1. Krokettenslayer

    Krokettenslayer Junior Member

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    Good evening,

    I have a 2006 Prius with about 235k km's. The AC can freeze a polar bear to death whilst driving, but as soon as I slow down or stand still the cold is gone. The radiator fan on the inverter side (driver, side, left hand drive) only works on low speed. When I turn the AC off none of radiator fans ever work. Things I have checked so far:

    • Relay 2 and 3 work, I have swapped them out with a friend's Prius.
    • I bridged the wire of the pressure switch (green and the opposite black/white wire): the inverter side fan starts blowing on high speed.

    I left the car running the AC in the 35 degree Celsius heat and none of the fans went on high speed, anyone get any ideas? Shouldn't both fans run on high speed when the AC is on full blast in this summer heat?

    Cheers
     
  2. GG707

    GG707 Junior Member

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    Yup they probably should... Try to restrict the airflow to radiator with foam insulators like we do in winder and see how it behaves . It should turn to full speed soon after that because the radiator will get really hot... Do it for a fiew. Moments in order to observe. Then try to drive around... But bare in mind the temps to avoid overheat at least the inverter... So If you drive around with the flow almost complete restricted it's ability to cool the cabin should be reduced very much... Then you will know that the temp sense on the radiator does not operate properly...

    Posted via the PriusChat mobile app.
     
  3. ChapmanF

    ChapmanF Senior Member

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    You've collected good data clearly showing a problem, and you should have no trouble tracking down the cause if you just print off the relevant part of the wiring diagram (more info) and grab a meter and begin.

    By intent, the two fans always run together. They either run together at low speed (because the circuit has them in series), or they run together at high speed (because the relays have reconfigured them in parallel). Several different inputs feed into the operation of the relays. For the behavior you are seeing, the wiring diagram will show you what causes are possible; your observations may already allow you to rule some of them out, and with a little active testing with a meter, you should get the rest of the way.
     
  4. edthefox5

    edthefox5 Senior Member

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    You nailed it with bypassing the pressure switch which means without a doubt the ac is not freezing it has low refrigerant. .

    Fan will not work on high if that pressure swx is open.

    Do something no one ever does on this site take it to a AC shop they will inject some dye into the system and find the leak and then properly charge it done deal. Pray it’s not the e coil under the dash.

    Do not inject a can of refrigerant you can buy at the parts store. big waste of time and money and can hurt the compressor.
     
  5. ChapmanF

    ChapmanF Senior Member

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    I don't think I have seen enough data yet to reach the same conclusion Ed has. In particular, as the fans are designed to always run in tandem (at either low or high speed), if at any time you see only one of them running, a problem exists that you cannot chalk up to refrigerant charge or the pressure switch. The way the system is wired, under correct operation, it is not possible for refrigerant charge or the pressure switch to give you only one fan running.

    That doesn't mean it was a bad idea to jump the pressure switch just to see what happens. That's one of five inputs that control what the fans do, and in troubleshooting you may find yourself wiggling more than one of them just to get ideas from what happens in each case.

    Taking the car to an A/C shop while there is a known electrical problem that would affect the A/C is probably asking too much of a lot of A/C shops; they might not figure it out, or would spend extra time and charge extra for tracking it down. Or they would shoot some refrigerant in it, not notice anything else was wrong, and hand your keys back. If the shop is also known for sharp electrical diagnosis, that might go better.

    There are some existing threads that have more details on how the fan circuitry is wired. Some wiring diagrams have been posted; most of the ones I can search up are for Gen 3, but Gen 2 wasn't a lot different. Here's a thread that's talking about a Gen 2. (The owner already had obtained the wiring diagram, so pictures weren't posted in the thread, but that's the diagram we're both referring to in the conversation.)

    You can see from that discussion (and from the diagram, if you look it up) that there are five control inputs figuring into what the fans are doing: two programmed outputs from the A/C controller, one from the engine controller, an engine coolant temperature physical switch, and the A/C refrigerant pressure physical switch. Those five inputs act on three relays, which together determine what the fans do (which is never to run one fan without the other, when it all works right).

    Here's a pic where somebody highlighted the low-speed and high-speed current paths, to make it easier to grok what the relays do. I'm not sure it's from your generation, but as I said, the circuits have stayed fairly similar.

    [​IMG]

    Regrettably, it isn't showing you the other interesting part, the way those five inputs are combined to drive the relay coils (you see the blue and green wires from the relay coils just disappear off the page to the right).

    Unless your problem turns out to be one of the relays itself, or the wiring downstream, or a fan fuse (which won't be the problem, if it's blown that just tells you somewhere else there's a problem), the troubleshooting will have to continue onto the page where those blue and green lines go. :)
     
  6. edthefox5

    edthefox5 Senior Member

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    Both fans should come on at operating temp engine coolant at 190 degrees.
    Both fans are running then. Both fans on if engine temp reached.

    If car just started and ac is then turned on only the inverter side fan comes on in low. You have to reach op temp for both fans on low both fans on low you turn on AC the inverter side fan goes high then and rad fans is one speed only. Like most cars.

    you Have a few things going on.

    One is your ac is low pressure and pressure swx not activated so high speed ac fan cannot be obtained on the inverter side fan. Low pressure.

    And maybe bad engine side fan too or check it’s fuse 30amp RDI

    To check that fuse take out relay Fan No 1 and see if you have 12 volts on the side of the contact not coil side.

    There’s also an ac control assy under the center console and the engine control module.


    Lastly take the plasticblack cover off the top of rad and check out the front of the condenser. Make sure you can’t see the ground when looking down that means the bottom cover came off and you need that cover it prevents fod on the face of the condenser,
     
  7. Krokettenslayer

    Krokettenslayer Junior Member

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    Thanks for the responses everyone, I appreciate it very much. So after having a good look today with a friend who is a car dealer and has a fancy Snap On scanning tool:

    First off I want to say that I was WRONG about both fans not working at low speed, they spin so quietly on low speed I completely missed it at first in a noisy environment.

    So this is what we did today:
    -Checked all fuses, everyone seems to be fine.

    -We drove the car with the AC on the highway hooked up to the scan tool, the evaporator temperature reached a very chilly 5,3 degrees Celsius. According to my car dealer friend this is very good, not surprising because I had the air conditioning system filled by a hybrid certified dealer half a year ago. When driving at low speeds or standing still the AC doesn't get cold anymore, as soon as the car picks up some speed and thus airflow in the condenser the AC gets cold again. When we parked the car with the car on READY and the AC on, both fans where running on low speed like they apparently should. After 10 mins the fans still didn't go on high speed despite having the AC on full blast with an outside temperature of 35 degrees Celsius. Then later when the car cooled down we let the car run in P with my foot on the throttle pedal to let the ICE heat up, the engine cooling fan started to kick in on high speed at 95 degrees Celsius, so that seems to work OK. The weird part is when I started it today once with the AC on, both fans actually kicked in at high speed and kept the AC air cold whilst standing still, but this lasted only a minute or so before both fans went to low speed again resulting in warm air.

    So to summarize the problem is that the fans DO indeed run at low speed when the car has been driven warm, both fans kicked in on high speed for a very short period but went back to low speed again. But usually they only work on low speed.

    @ChapmanF
    So if I understand that correctly in my case fan relay #1 and #2 are powdered on very occasionally only? I will have to find a way to check which one of the 5 inputs are powering/ not powering those relays.
     
  8. ChapmanF

    ChapmanF Senior Member

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    Hmm, so that's worth digging out the actual Gen 2 wiring diagram.

    fans.png

    A few things worth noting:

    1. The system outline only describes two modes of operation: both fans on low, or both fans on high.
    2. Both on low will happen when either: physical Water Temp Switch W4 is made, or A/C control is programmed to pull down "CF".
    3. Both on high will happen when: both are on low (for either above reason), and at least one of:
      • Engine control module is programmed to pull down "FAN", or
      • A/C control is programmed to pull down "RF", or
      • physical refrigerant pressure switch is made.
    4. There is one possibility they left out of the system outline: if it ever happens that one of the three conditions in (3) is met without either of the conditions in (2), then you could see the "radiator" fan (the blue-wired one) running at high speed and the "condenser" fan (the green-wired one) not running.
    5. There is not a possibility of ever seeing one fan run at low speed without the other one. It physically can't happen if nothing is broken; low speed is achieved by passing the same current through both fans in series.
      • It could be possible if one fan is physically unable to rotate, but still conducts, so the other fan could still run on low. (If that happened, probably switching to high would blow the locked fan's fuse.)

    Something that isn't clear from the manual is whether the unmentioned one-fan-on-high possibility (4) is really ever supposed to happen, and just got left out of the system outline, or if they really didn't intend it to happen in normal operation and they programmed the ECUs to drive their outputs in a particular sequence so it wouldn't; in that case, seeing it happen would suggest something is amiss.

    The wording in the system outline suggests that the "water temp sw" W4 is associated with the inverter, not the engine coolant, in which case the control based on engine coolant temperature would depend on the ECM reading the coolant temperature sensor and deciding when to pull down "FAN". But I haven't looked through the location and routing section to see exactly where W4 really is. The diagram does go out of its way to show the engine ECU communicating over CAN with the HV ECU, so it could be getting inverter temperature that way, and W4 could be an engine temperature switch, if a mistake was made in the system outline.
     
  9. Krokettenslayer

    Krokettenslayer Junior Member

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    Today I went to the hybrid specialist that deals in mostly Toyota's and explained the situation; he suspects the pressure switch of the AC. So this week I'm going to let them switch it out after purging the coolant. I'll keep you guys updated.
     
  10. Krokettenslayer

    Krokettenslayer Junior Member

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    So it appears my compressor was slowly dying, in a matter of a couple of (very hot) days it crapped out on me (makes weird noises now), now the system doesn't cool at all, they also showed me some small leaks in the condenser with a UV light. Going to let the A\C specialist put in a new Denso compressor and condensor+dryer and flush the system next week, I'm still going to drive this car the next few years so the repair cost is OK to me. Will keep you guys updated of course.
     
  11. Krokettenslayer

    Krokettenslayer Junior Member

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    Picked up the car today, the A/C compressor and condenser have been replaced. The A/C and fans work like they should again, so the core problem was that the A/C compressor wasn't putting out enough pressure to trigger the pressure switch into turning on the A/C fan into high speed. Case closed as far as I'm concerned.
     
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