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  1. #1
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    Question on evaporator core design



    I'm working on the A/C system in a 1991 Corvette, and having some issues. I'll try to be brief.

    When the system was evacuated and charged with R-12 to OEM specs, the system short-cycled, and while the suction line was cold, the evap did not get cold, and vent temps were high. Evacuated again, tore system down, and found 90% of the oil was in the evap (over 8 oz), with hardly any in the accumulator or compressor. When I put those components in, I added 3 oz to the evap, 2.5 oz to the accumulator, 1 oz to the condenser, and 3 or 3.5 oz in the compressor (probably a little overfilled overall, I think the oil capacity is 8 oz system-wide).

    Is this just a case of too much oil affecting evap performance?

    Is this diagram of the flow in the evap appropriate? I cut the core apart and it was not what I expected to find...



    Thanks for helping a novice...

    -Andrew



  2. #2
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    Re: Question on evaporator core design

    Yes, too much oil can affect performance, as you found it will end up in the evaporator until such time as the system operates under full load.

    Under full load the expansion device will be as open as it will go and the increased flow of refrigerant will flush the oil back to the compressor.

    When you added the oil all you had to do was put it into the compressor, it does not have a useful function anywhere else, as you have already found out.
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  3. #3
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    Re: Question on evaporator core design

    Quote Originally Posted by Brian_UK View Post
    Yes, too much oil can affect performance, as you found it will end up in the evaporator until such time as the system operates under full load.

    Under full load the expansion device will be as open as it will go and the increased flow of refrigerant will flush the oil back to the compressor.

    When you added the oil all you had to do was put it into the compressor, it does not have a useful function anywhere else, as you have already found out.
    Brian, thanks so much for your reply. I guess my evaporator dissection was educational but not necessary. I suppose I misinterpreted the factory service manual, in that it specified oil amounts for each component, but that would be only appropriate in the case of only one component being replaced, rather than a whole new system.

    it still is puzzling to me, since I have no actual education in HVAC, why the first upright plate in the condenser is separate from the rest, requiring refrigerant to flow in from the bottom, then up to the top of the core immediately - where it seems to me the path of least resistance would be to immediately exit the core via the suction line, rather than spend any time going *down* the other plates to the bottom of the core.

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    Re: Question on evaporator core design

    So, here's some pics of the evap I cut open, looking for what I thought could have been a blockage. This is what I based my diagram on.

    Outside of entrance to evap:


    Cutaway view of inside of entry port:


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    Re: Question on evaporator core design

    Outside view of exit port to suction line:


    Cutaway view of exit port:


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    Re: Question on evaporator core design

    Close up of location where I think there should be a solid piece separating the 2 halves of the evap, or something of that sort, rather than what appears to be a very subtle restrictor plate... of course, just a solid plate would render the core useless, but I don't see how this thing is supposed to function properly. How is it that refrigerant can run up from the inlet, to the top of the core, and then have anywhere to go but right out the suction line?

  7. #7
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    Re: Question on evaporator core design

    corvettes .. intresting .Marinised Design
    .. could you kindly specify the type of condenser and evaporator .
    Oil carryover is a a common problem in such packages as the design is very-very compact .
    ( i am unable to view the pics ).

  8. #8
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    Re: Question on evaporator core design

    If a/c has accumulator then refrigerant feed is done with orifice only. No need to dissect evaporator if coil was clean. Short cycle is due to wrong gas charge or restricted orifice.
    To the optimist, the glass is half full. To the pessimist, the glass is half empty.

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    Re: Question on evaporator core design

    What about some pics of the car itself.

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    Re: Question on evaporator core design

    http://youtu.be/V1RIi-jGePU Something like this?
    To the optimist, the glass is half full. To the pessimist, the glass is half empty.

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