20*F superheat on pakaged units.
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  1. #1
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    Unhappy

    several times in a raw on packaged rooftop units I couldn`t get down to 20*F compressor superheat although units were cooling and pressures were in the right ranges.I haven`t charged many rooftops yet.on residental split systems I didn`t have this situation.Is it not applicable to packaged units?thanks in advance.

  2. #2
    Huh?

    Come again....


    Please to define what you intended to measure.
    Where you made your readings.
    How you made your readings.


    Do you mean; superheat back at the compressor? Measured six inches from the suction service valve?
    And you subtracted your suction line temp reading from your pressure gage reading, AFTER converting it from pressure to temperature?

    Let er rip.....

  3. #3
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    Originally posted by R12rules
    (Huh?)
    (Come again....)

    I will.

    (Please to define what you intended to measure.)

    superheat by the compressor to charge unit.

    (Where you made your readings.)

    on suction line 6 inches from the SSV.

    (How you made your readings.)

    taped my thermistor thermometer on line.

    (Do you mean; superheat back at the compressor?)

    yes.

    ( Measured six inches from the suction service valve?)

    yes.

    (And you subtracted your suction line temp reading from your pressure gage reading)

    the otherway around

    (, AFTER converting it from pressure to temperature?)

    yes.

    (Let er rip.....)
    let`s...

  4. #4
    What do you mean by down to 20F?

    Where is it right now? Is it as high as 40F?

    Between 20 and 35 is ideal. What have you read?

  5. #5
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    Originally posted by R12rules
    What do you mean by down to 20F?

    Where is it right now? Is it as high as 40F?

    Between 20 and 35 is ideal. What have you read?
    40 and even higher,a lot more.
    one detail though;
    I have been working on laundrymats recently.a lot of heat being picked up by the evap.?couldn`t see if it dropped later on.

  6. #6
    So your saying that the heat load in the buildig is probably so great that the compressor is running flat out?
    If the system is overloaded, then that is the reason there is no cooling back at the compressor!
    That A/C system is working outside it design specs.

    Possibly that tenant needs to add another A/C unit to their roof top.

    A compressor will run without cooling. But not as well and not for as long.

    Have you verified the system charge to be correct?

    Have you thought about bring in a power washer to clean the condensor? Dont use it full strength. It needs to be the adjustable type of power washer. Otherwise you'd fold over all the fins. No bueno!


    What is your subcooling while the system is operating? But of course, I dont know if you have a fixed orofice or TXV metering device.
    That will make a difference too.


  7. #7
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    Originally posted by R12rules
    So your saying that the heat load in the buildig is probably so great that the compressor is running flat out?
    If the system is overloaded, then that is the reason there is no cooling back at the compressor!
    That A/C system is working outside it design specs.

    Possibly that tenant needs to add another A/C unit to their roof top.

    A compressor will run without cooling. But not as well and not for as long.

    Have you verified the system charge to be correct?

    Have you thought about bring in a power washer to clean the condensor? Dont use it full strength. It needs to be the adjustable type of power washer. Otherwise you'd fold over all the fins. No bueno!


    What is your subcooling while the system is operating? But of course, I dont know if you have a fixed orofice or TXV metering device.
    That will make a difference too.

    Power washer..yes, after the condensor cleaner,a couple of times.One common problem I saw was bad fins already.Since my suction pressure came down to 60s I think it means the evap.can`t do any better.or it will start freezing.?so other than a little higher head pressure I didn`t concern with the fin conditions.

  8. #8
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    What's the temperature inside? If the load is as high as you say it is inside (Upper 70's? 80?) and your suction pressure is in the 60's, then there is probably either a slight undercharge or low airflow across the evaporator. What is the ambient temperature? Indoor Temp? Pressures?

  9. #9
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    Originally posted by dschwab9
    What's the temperature inside? If the load is as high as you say it is inside (Upper 70's? 80?) and your suction pressure is in the 60's, then there is probably either a slight undercharge or low airflow across the evaporator. What is the ambient temperature? Indoor Temp? Pressures?
    ambient temperature about 80*F,head pressure around 300 ,65 back pressure.inside lower80`s when I got there upper 70`s when I left.all coils cleaned and washed filters replaced.

  10. #10
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    Well, that's a really high head for 80 degree ambient. That's also a low suction for 80 degree return air. I'd suspect a restriction and the system has been overcharged trying to get the suction up, thus the high head and somewhat reasonable suction. What kind of metering device is it?

    With the suction that low now, when the inside temp comes down to low 70's, you may start frosting the evaporator.

    Why is this in the refrigeration section?

  11. #11
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    Originally posted by dschwab9
    Why is this in the refrigeration section?
    Because I just started getting acquainted with this section.I don`t know anybody who does refrigeration and not AC.

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