AC not working at idle/low speed

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Meultaine, May 22, 2020.

  1. Meultaine

    Meultaine New Member

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    Hello,

    I am the proud owner of 2006 gen3 Prius since March 2018. It now has about 140k miles.

    AC never worked well (if at all) at the time of purchase.

    Last year, while sweating in the car after work, I decided to dig into it. I replaced the condenser because it was probably leaking (there was a greasy spot) and had the system refilled. There's no leak anymore because the system has the same behavior since 1 year now.

    But... still not working properly :
    *at 'high' speed (50mph and higher) ==> ok blowing cold
    *50mph ==> 20mph : working but it is weak (can't really lower the internal temperature of the car unless you drive for a really long time).
    *under 20mph or idle : sometimes does not work at all, sometimes it works but is very very weak.

    What I checked :
    *Compressor is turning on
    *condenser/radiator fans are turning on
    *AC drain 'hose' under passenger floor ==> not clogged

    So what I think is that it's not getting enough airflow in the condenser.

    It seems like there's a relay putting the 2 fans in series instead of parallel (then only getting 6V each ==> low speed mode). Is it supposed to be on low speed when you turn on the AC ? Or high ? When I disconnect one of the fan, the other one is also stopping so I guess it's in low mode. May be I can force it in high with some unsafe wires in the fuse box but if someone can tell me what's the expected speed at idle with AC, that would be great so I can troubleshoot further.

    Any tips are welcome :)
     
  2. RobertK

    RobertK Member

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    Have the fans ever been removed from the car? The two fans rotate in opposite directions, and if they get swapped out they will push air forward from the engine compartment instead of pulling it through the condenser and radiator. Might be a long shot, but it's easy to see which way the air is flowing.
     
  3. edthefox5

    edthefox5 Senior Member

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    yes you are right about the fans. theirs 2 fans a rad fan controlled by engine ecu and the ac fan by the AC controler. The ac fan kicks on when ac is on. Its loud.
    So you have the classic not enough air getting thru condenser. Its ok when in the wind but at the light not enough air moving thru it.
    See that aot on here no one cleans there condenser but yours is fan.

    This not a salvage title car is it?

    But You never said or Im missing it....after your replaced the condenser and recharged it was there any improvement and who did the charging? Did they use ND-OIL11 oil?

    lets check the charge just to make sure its ok. Try this:

    Set:
    All doors open
    AC on max cold
    Fan setting on HI
    AC On

    Check sight glass:

    If bubbles exist insufficient charge
    No temp difference between compressor in & out is charge is low
    Considerable difference in temp is charge ok
    Immediately after ac turned off sight glass clear is excessive charge
    Immediately after turn off ac sight glass foams then becomes clear is charge ok.

    I have the schematic for the fan system its to hard to explain it uses relays and a pressure switch too so if charge low it wont come on.

    PM me with your email and Ill send you a copy of that fan circuit.
     
  4. Patrick Wong

    Patrick Wong DIY Enthusiast

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    1. Check the refrigerant level as Ed suggested.
    2. Check that the radiator fans are sucking air into the engine compartment instead of blowing air from the engine compartment through the radiator as RobertK suggested.
    3. If the two fans are on at low speed, it might mean that Fan #2 relay (which is single pole double throw) is stuck in one position which forces the two fans to be in series.
    4. In order for both fans to be on full speed, Fan #2 relay must energize (to ground the A/C condenser fan) and Fan #1 relay must energize to apply 12VDC to the radiator fan motor.
    5. Fan #3 relay seems to be working correctly since you say the AC condenser fan is working.
     
  5. edthefox5

    edthefox5 Senior Member

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    Its a confusing circuit at first glance. And 2 fans 3 relays. And the engine fan has a temp switch and the ac fan has a pressure switch.

    The ac pressure switch must be closed (charge good) in order for the AC fan to go max speed. Closed means its grounding relay coil #3
    and turning that relay on.

    If fan operates but no high speed operation i would suspect the pressure switch is open reflecting low charge. If you can jump around that switch to test the high speed motor to see if it works. I believe its plugged into the passenger side of the condenser or thereabouts. It has a blue wire and white/black strip wire on its plug. The white/black stripe wire is ground the blue wire goes to a flying junction block that then grounds relay coil #3.
    Unplug it and short across its pins. That should make the ac motor go high speed. Or when the condenser was replaced it was never plugged in. Or fell out or loose.

    Good Luck.
     
  6. Meultaine

    Meultaine New Member

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    Thanks for all the feedbacks :)

    It is not a salvaged car.

    What I did today :
    *Fans flow direction ==> both ok, blowing 'in the motor'
    *The two relays (one 4 pins and one 5 pins) in the motor fuse box ==> ok (tested with a 9V battery and multimeter to check if the pins are well connected)
    *relay pressure switch : I unplugged it and everything went off (compressor and fans). Not sure how I am supposed to short it since there's 4 connections ?
    *pipe temperature : hot from the compressor to the condenser (OUT compressor), ambiant (or cannot notice a difference) on the LOW (IN compressor), cannot really tell where it comes from.
    *for the sight glass... I cannot really tell, I can't see very well, no bubble but I can not ensure that there's foam after shutoff... Since the AC does not blow cold at idle, it's normal that I can't see the expected behavior in this glass ?
    *What I did to test the pressure is the "press AC auto + air recirculation and press start twice" ==> not a single climate error code (displaying "00"). If we thrust this self-diag, it is well filled.

    I also had the note from last year's refill and the shop filled it with 450g of refrigerant, which is the recommended amount (450g+-30g ). Since the behavior of the AC system is the same since then and the self-diag returns not error, I strongly think the charge is ok.

    I am not sure they filled the system with ND11 oil or equivalent. I'll check with the shop. I would not be surprised if they use a suitable oil since more and more cars have electric compressor nowadays. If not, wouldn't it already have broken my AC system ? Or killed me when touching the car ?

    I found this :

    Basically, the guy is running the AC on low ventilation + low temp (with 77°F outside, at about the same as my place today). His fans cycle through low/high speed. If I do the same, my fans stay at low speed all the time, even if I put the ventilation on high (temp always on low). So the issue is probably somewhere in the fan speed monitoring (but as it is said in this post, there's so much components...).

    I'll ask edthefox5 for the schematics and try to find why there's no signal to switch the relay to high speed.
     
  7. Meultaine

    Meultaine New Member

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    I just saw I mentioned gen3 in my original post but it is a gen2 from 2006*
     
  8. edthefox5

    edthefox5 Senior Member

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    The pressure swx plug only has 2conductors and I gave you there wire colors.
     
  9. Meultaine

    Meultaine New Member

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    Today I shorted the pressure sensor (green wire and black/white).

    The fans immediately went full blast (high speed). I guess nothing's wrong with the electric system of the fans.

    I also checked the RDI fuse (fusible link) and nothing wrong there, it is not blown.

    Is this a sign of a bad pressure sensor ?
     
  10. Patrick Wong

    Patrick Wong DIY Enthusiast

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    It sounds like your refrigerant is a little low.
     
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  11. edthefox5

    edthefox5 Senior Member

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    Its the sign your low on refrigerant which is why I wanted you to test it. Before that I would have gone over all the connections that were touched during the condenser replacement and make sure they are very tight. All the pipe connections.

    Time for a dye leak test. You got a leak.
    After the condenser was replaced didn't they do a dye leak test?

    I would stop using the ac until the charge level is proper and make sure there using ND-11.

    The ac system on a G2 is an excellent system. The trick is to use it every single day. Im going on my 13th year with my G2 and the ac still works perfect. Only had to replace the blower motor. I have kept up on ecoil cleaning and condenser cleaning. Very few reports of issues on this site. The few that have been reported are really bad like ecoil replacement (poor maintenance) or shenanigans with the wrong refrigerant with systems that have developed leaks. Some fan issues but many from salvage popped hard in the front and poorly repaired cars.

    It is a really good electric compressor system.

    I would sell the car before before I would go thru an ecoil replacement.
     
    #11 edthefox5, May 30, 2020 at 1:59 PM
    Last edited: May 30, 2020 at 9:16 PM
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