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Update: A/C not cooling. Can't add freon... S90-V90

posted by  RK on  Fri May 21 15:32 CST 2004
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A few weeks ago I posted a message about problems with recharging (topping off) A/C system in my wife's car. Somehow the system did not want to take any additional freon even though I knew the system was running low on freon.

Well tonight I tried the whole procedure once again and this time it worked! The car was very "thirsty" and it took the whole 12oz. can of R134a in less than 7 minutes. The only difference from the last time that I can think of was that today I used a brand new charging hose which I got from Wal-Mart yesterday. So, I suspect that my old charging hose was either clogged or seriously leaking. Anyway, my wife is happy and I am happy for her, because the weather is getting hotter and hotter.

Does anybody know a good reference point which I can use to check if I put enough gas in the system? Last time I checked (prior to re-charging) the stationary A/C low-side pressure (with the engine off) was 66 psi at 79F, which I knew was too low. Does anybody know what is the normal stationary pressure for S/V90 A/C system at specific temperatures (for example at 70F or 80F)?







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    Update: A/C not cooling. Can't add freon... S90-V90

    posted by  chris herbst on  Sat May 22 16:13 CST 2004
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    last visit: Mon Oct 20 20:32 CST 2014
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    Topping off an S90 system is virtually impossible, only because there isn't any way that I know of, to do it while reading the high side pressure (no port).

    The S90 is best sucked out, then recharged by weight. That works well.

    If you are going to 'top off', do so carefully. The low side pressure tells you only the output of the evaporator, not much else. The high pressure reading is where the best information is.

    Part of the reason that the system won't suck out the can of refrigerant, could be because there was too much low-side pressure. A simple way to get around that, is to charge with the doors open and a garden hose in the condenser. But you can easily overcharge that way too. And a slight overcharge on an R134 system is worse than a slight undercharge.








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    Update: A/C not cooling. Can't add freon... S90-V90

    posted by  mcduck on  Fri May 21 16:07 CST 2004
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    last visit: Sun Sep 9 11:47 CST 2012
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    Static pressure is nearly irrelevant; as long as there's ANY liqiud in the system, the static pressure will be the vapor pressure of the freon.
    You need to check the high/low pressures with the system running.
    --
    Jim McDonald








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      Update: A/C not cooling. Can't add freon... S90-V90

      posted by  RK on  Sat May 22 08:56 CST 2004
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      What numbers should I expect on a car with properly charged A/C? (Prior to re-charging the pressure was cycling from about 25psi to 40psi every 4-5 seconds.)








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        Update: A/C not cooling. Can't add freon... S90-V90

        posted by  dewfpo on  Sun May 23 06:42 CST 2004
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        last visit: Thu Oct 23 18:34 CST 2014
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        25 to 40 psi is the correct range (+/- 1 psi) for the pressostat. On days where the ambient temp is about 85F and above the compressor stays engaged continuously at idle, cycling only at higher than idle rpm.

        I have not seen a chart for the R134a systems (I'm sure there available) that show compressor cycling time versus ambient temp. If you can google search the internet for such a chart it should give you the data you need. I've got one for an R12 system but that won't help you.

        I've got the Volvo green books on the ac system but it doesn't have the compressor cycling time chart listed in it.

        DEWFPO
        --
        1998 S90 068,300 and 1995 964 152,300








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        Update: A/C not cooling. Can't add freon... S90-V90

        posted by  mcduck on  Sat May 22 12:53 CST 2004
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        last visit: Sun Sep 9 11:47 CST 2012
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        As a matter of convenience, not best practice, I charge 'till the clutch just stops cycling; my 134a conversion reads ~35 PSI on the low side @ 1500RPM @70F, with A/C and fan on max.
        YMMV.
        --
        Jim McDonald








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    Update: A/C not cooling. Can't add freon... S90-V90

    posted by  dewfpo on  Fri May 21 15:47 CST 2004
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    last visit: Thu Oct 23 18:34 CST 2014
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    At 70 degrees F, engine cold, car in the shade, the static pressure was 75 and 73 psi on our 98 S90 and our 95 960 respectively. Both AC systems work fine.

    DEWFPO
    --
    1998 S90 068,300 and 1995 964 152,300







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