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  1. #1
    Join Date
    Jan 2012
    Location
    Vancouver
    Posts
    28

    Default Intermittent A/C operation

    I just got back from my long trip that I had the Haldex question about and discovered very early in the trip that the A/C works only intermittently. This despite having the system recharged (at considerable cost) two days before the run.
    I wondered if perhaps the heater was coming on and heating the cold air so I used a pair of vice grips and a piece of bent metal to clamp off the heater hose at the firewall--it made no difference.

    The shop that recharged the system says I have an intermittent problem and they want $165 just to look at it.

    Any suggestions/possible causes?

  2. #2
    Join Date
    Dec 2009
    Location
    GA
    Posts
    1,281

    Default

    Quote Originally Posted by davidbir View Post
    discovered very early in the trip that the A/C works only intermittently. This despite having the system recharged (at considerable cost) two days before the run.
    I wondered if perhaps the heater was coming on and heating the cold air so I used a pair of vice grips and a piece of bent metal to clamp off the heater hose at the firewall--it made no difference.
    If your ac is cold then stops being cold but continues to blow air - A common failure is the ac clutch is worn and the gap is too large, then when hot the magnetic force is not strong enough to close the gap. It can be difficult to duplicate the problem in the shop because the clutch won't get hot enough just idling. I think spec is .3-.5mm, and if it is larger than 1mm, adjusting the gap, (removing shims) might solve the too large gap/hot clutch failure. There are also several other things that can cause your ac not cold problem related to sensors in the climate system, so it would help to have a better description of your failure.

    Here in the south the large gap failure symptoms are: AC stops blowing cold when very hot outside (90+) after the car has run for a while, usually first noticed on the hottest days of the year when in stop and go traffic. When malfunctioning the clutch is not engaged and there is power going to it. The clutch does not usually reengage until the engine cools down from being driven with cool air flow to the engine or is turned off for a while. When malfunctioning with the engine running you can usually push the clutch closed (very carefully) with a large screwdriver or pry bar to easily verify there is power going to the clutch when it is not working (repeat - very carefully you are pushing against a spinning clutch!)

    Hot water flows through the heater hoses/core all the time, the blend doors mix hot air flow and cold air flow to create the temperature requested, I would not expect a blend door problem to be causing your lack of cold air.

  3. #3
    Join Date
    Jan 2012
    Location
    Vancouver
    Posts
    28

    Default

    Many thanks for that Hoonk. The thought of trying to press the compressor clutch closed does not fill me with anticipation! It appears to be cycling and the engine rpm change when it engages.

    The a/c does run cold for maybe 15-30 minutes and then rises to ambient.

    We had to have the a/c compressor replaced not long after we acquired the car - the original siezed due to lack of lubricant apparently. It has never worked well but we live in Vancouver and for much of the time don't need it. In winter time it manages to demist.

  4. #4
    Join Date
    Jan 2012
    Location
    Vancouver
    Posts
    28

    Default

    I just spent time reading all I could on a/c problems with these cars and checked two sensors:

    The evaporator sensor, located above the foot pedals causes the lines inside the engine bay to ice up if it malfunctions apparently-I drove the car until the a/c was blowing ambient and stopped and checked the lines-no sign of icing.

    The in-dash temperature sensor gets covered in dust or gets damaged --I checked it and indeed it was partly covered in fluff which I was able to blow out and it made no difference.

    I looked at the compressor clutch and there is a gap of slightly less than 1 mm I would guess-I will try measuring it tomorrow when the engine is cool.
    The compressor seems to be operating although it only engages for a few seconds every ten-fifteen seconds or so-I don't know if that is normal.

    The a/c was operating worse today than previously!

  5. #5
    Join Date
    Jun 2017
    Location
    Southern California
    Posts
    7

    Default

    May want to check the expansion valve -- my AC was not blowing cold at all with a full charge and it was due to a clogged expansion valve. I replaced it and all is good now. Apparently the stop-leak that is in those cans from the car part stores that I have used can clog that valve.
    Last edited by A.Lucas; 06-26-2019 at 06:08 PM.

  6. #6
    Join Date
    Dec 2009
    Location
    GA
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    1,281

    Default

    Quote Originally Posted by davidbir View Post
    The compressor seems to be operating although it only engages for a few seconds every ten-fifteen seconds or so-I don't know if that is normal.
    If the system is low on refrigerant the compressor will cycle like that, if it is warm outside. Low freon = low pressure, pressure drops lower with compressor on, low pressure switch turns the compressor off, pressure rises compressor comes back on, and repeat.

    Possible that the low pressure switch is bad, a set of gauges connected to at least the low side will tell you.

    If the system was recently recharged with the correct amount of r134, .9kg i think, and it is low now - you have a leak.

    Freon is a colorless odorless gas - it can be difficult to figure out where it is leaking from. A common leak is the condensor cracks, in the upper right corner where the drier is attached to it. You can sometimes see an oil stain on the crack where the freon took the oil out with it.

  7. #7
    Join Date
    Dec 2009
    Location
    GA
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    1,281

    Default

    Quote Originally Posted by davidbir View Post
    The a/c does run cold for maybe 15-30 minutes and then rises to ambient.
    Your later post describes possible low freon, that statement could be heat related clutch failure - is it one or both?

  8. #8
    Join Date
    Jan 2012
    Location
    Vancouver
    Posts
    28

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    As of today I would say it runs cold for only a few minutes and then goes to ambient with the compressor cycling as described.

  9. #9
    Join Date
    Dec 2009
    Location
    GA
    Posts
    1,281

    Default

    I would choose a service provider that has Vida, either a real subscription (a dealer or large specialist) or the hacked copy from the internet to be able to monitor all the parameters including power to the compressor (much easier than trying to get to the wire on a hot engine). Several sensors, Air temp, evap temp, high and low pressure can create problems.

    It's possible that the clutch is worn causing what you described but a worn clutch usually does not cycle with your on 3 on, 15 off times. As others have suggested you could have a mechanical problem with the flow of refrigerant, like an expansion valve - but those once they are clogged usually don't work properly until replaced. However your previous compressor failure could have put shredded metal in the system, partially blocking the condenser or expansion valve.

    A set of gauges and Vida hooked up to the car (and having the failure occur) should be able to help with diagnosis.

  10. #10
    Join Date
    Feb 2010
    Location
    Virginia Beach
    Posts
    3,818

    Default

    Quote Originally Posted by hoonk View Post
    I would choose a service provider that has Vida, either a real subscription (a dealer or large specialist) or the hacked copy from the internet to be able to monitor all the parameters including power to the compressor (much easier than trying to get to the wire on a hot engine). Several sensors, Air temp, evap temp, high and low pressure can create problems.

    It's possible that the clutch is worn causing what you described but a worn clutch usually does not cycle with your on 3 on, 15 off times. As others have suggested you could have a mechanical problem with the flow of refrigerant, like an expansion valve - but those once they are clogged usually don't work properly until replaced. However your previous compressor failure could have put shredded metal in the system, partially blocking the condenser or expansion valve.

    A set of gauges and Vida hooked up to the car (and having the failure occur) should be able to help with diagnosis.
    Completely agree.

    With a recently replaced compressor, actual troubleshooting is required.

    I had a similar problem on the XC, and it turned out to be an evaporator temperature sensor. A $25 part that took 20 minutes to install. Easy fix.

    But KNOWING WHAT PART needing replacing was critical. You’re at the “speculation” phase of repair. A very expensive and frustrating place to be. Two paths before you:

    1. guess and throw parts

    2. troubleshoot and diagnose.

    Please find someone that can do the latter. The former is common, and very hard on your sanity.

    And your wallet.
    Current Fleet:
    2016 Tundra Crewmax 4WD 1794
    2005 MB S600 (100K, Michelin AS3+, M1 0W40)
    2002 V70-XC (238K, Castrol Edge 0W40)
    2002 V70-T5 (195K, IPD bars, Bilsteins)
    2001 V70-T5 (76K)
    1932 Packard Sedan (straight 8, dual sidemounts, original paint and interior, Shell Rotella 15W40)

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