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Thread: Trying to fill A/C system; blows hot air and high side has low pressure

  1. #1
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    Trying to fill A/C system; blows hot air and high side has low pressure

    Hi everyone. I'm trying to fill my A/C system with R134a. This is a new system that has been held at vacuum (and actually holding it) for a year while I got other things in order.

    I got it to take about two and a half 12 oz cans of refrigerant. The compressor turns on, so that parts's working. However, the high side reads very low, and I'm getting hot air out of the vents (not warm air -- hot air, like the heater is on, but it's not). The metal of the manifold block itself is also hot to the touch.

    My setup is a proper manifold set with the lines correctly connected to the high and low sides of the A/C system. I have an early car, but it has been updated to the later system with the high pressure switch. Literally the entire system is new front-to-back, including the hoses, accumulator, compressor, condenser, evaporator, orifice tube, high pressure switch, etc. I made sure to pull vacuum on the system to vacuum, but it was already sitting at vacuum so that wasn't really necessary.

    Any idea what I'm doing wrong?

    Here's a picture of the gauges with the engine and compressor running:

    IMG_1750.jpg

    And with the engine off:

    IMG_1753.jpg

    Thanks!

    -- Joe

  2. #2
    Delorean Guru
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    Verify you have connected the low (blue) hose to the suction (low) side and the same for the high (red) side. I think you go them reversed. According to ST-29-11/81 the correct fill is 2.2 lbs but that's for R-12. For -134 you reduce the fill 10% so that is 31.6oz. You got 30 in there so you should have the correct fill. As for why it is blowing hot, get the gauges on right and see what your pressures are. The low pressure switch must be adjusted to use -134.
    David Teitelbaum

  3. #3
    Senior Member Rich's Avatar
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    It looks like the manifold gauges are reading in reverse of normal with compressor on. The low side reads like the high side should and vice versa. Am I reading that correctly?

    That, along with zero cooling, suggests the new hoses or something else might be connected backward.

    You report that you're sure the refrigerant is flowing the right way with correctly connected hoses. Possibly worth another look just in case?

    Now seeing David T. already replied similarly.
    March '81, 5-speed, black interior

  4. #4
    Senior Member DMC-81's Avatar
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    Quote Originally Posted by jangell View Post
    Hi everyone. I'm trying to fill my A/C system with R134a. This is a new system that has been held at vacuum (and actually holding it) for a year while I got other things in order.

    I got it to take about two and a half 12 oz cans of refrigerant. The compressor turns on, so that parts's working. However, the high side reads very low, and I'm getting hot air out of the vents (not warm air -- hot air, like the heater is on, but it's not). The metal of the manifold block itself is also hot to the touch.

    My setup is a proper manifold set with the lines correctly connected to the high and low sides of the A/C system. I have an early car, but it has been updated to the later system with the high pressure switch. Literally the entire system is new front-to-back, including the hoses, accumulator, compressor, condenser, evaporator, orifice tube, high pressure switch, etc. I made sure to pull vacuum on the system to vacuum, but it was already sitting at vacuum so that wasn't really necessary.

    Any idea what I'm doing wrong?

    Here's a picture of the gauges with the engine and compressor running:

    IMG_1750.jpg

    And with the engine off:

    IMG_1753.jpg

    Thanks!

    -- Joe
    Hmm, that's weird. Are you sure the hoses ( both A/C and manifold) are not connected to the wrong ports? Also, here's a handy troubleshooting chart.

    https://www.apairinc.com/downloads/get.aspx?i=73849

    Edit: Other posters beat me to the punch.
    Last edited by DMC-81; 07-07-2019 at 03:37 PM.
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  5. #5
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    Thanks ó I thought I had them hooked up correctly, but itís possible that I donít. I have the blue (low) line connected to the side of the compressor closest to the edge of the car, and the red line connected to the side closest to the engine. Iíve attached photos. I need to get a longer quick release adapter for the side I have the red hose hooked up to, so Iím just connecting it directly for now.



    ó Joe

  6. #6
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    So I found the thread where I asked what compressor to get for a 3.0L conversion, and went with a Four Seasons 58555 (Sanden SD709). There was also a picture of a similar compressor installed, and it clearly has the high side at the edge of the car and the low side closest to the engine: http://dmctalk.org/attachment.php?at...4&d=1495250162.

    I can't actually find any useful information about which side of the compressor is the high or low side (from Sanden or Four Seasons).

    Now the question is if I just have the manifold hooked up backwards, or the actual A/C lines hooked up backwards. I don't recall if the hose connections to the compressor are different sizes or not.

    Also, I know you're not supposed to fill from the high side, so I'm wondering if I've done anything particularly bad there.

    I'll swap the manifold hoses and try again. Thanks!

    -- Joe

  7. #7
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    Ok, so I think the hoses in the AC system itself are set up right ó the driverís side hose from the condenser goes to the passenger side of the compressor.

    So itís just the Manifold lines that are swapped.

    Iíll report back once Iíve tried filling it with the hoses hooked up correctly. Thanks!

    ó Joe

  8. #8
    Administrator Ron's Avatar
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    At the compressor, the high side hose/pipe always has the smaller diameter (the coolant is compressed so it has less volume...).

    The high side compressor port should have an "D" and the low side an "S", if marked.

    I doubt you could put 2.5 cans in the high side with those pressures w/o blowing up the can???

    Be carefull!

  9. #9
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    More likely I’m very bad at gauging how much the cans weigh full vs empty, or that something was leaking. I certainly vented some refrigerant when disconnecting my side can tap, but my understanding is that that is normal. No cans have exploded on me, so that’s good.

    Also, both of my hoses are the same diameter, so I don't have a good way to tell by sight. I finally just traced the hoses from the compressor, given that the driver's side one goes to the condenser and would be the low pressure side. The way the hoses cross each other at the compressor threw me for a bit, and it's easy to miss that in the parts manual diagram as well.

    I’m at the car now with the engine running and have 40 PSI on the low side and 350 PSI on the high side (it’s 78 degrees ambient). The compressor has been running the entire time, and the vents are still blowing hot air. It was still going up when I turned the car, so now I’m guessing that I’ve overfilled it? Still Dortmund explain the hot air, though...

    Thanks!

    — Joe
    Last edited by jangell; 07-07-2019 at 05:09 PM.

  10. #10
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by Ron View Post
    At the compressor, the high side hose/pipe always has the smaller diameter (the coolant is compressed so it has less volume...).

    The high side compressor port should have an "D" and the low said an "S", if marked.

    I doubt you could put 2.5 cans in the high side with those pressures w/o blowing up the can???

    Be carefull!
    +1
    But I think DPI uses one size hose for both.

    Only open your low side as shown on your gauges when your adding charge. If the low side pressure goes much above 50 PSI shut off the charge until the pressure drops.
    Dave M vin 03572
    http://dm-eng.weebly.com/

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