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  1. #14
    Join Date
    Sep 2002
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    The entering air for the evap is 30 degrees - tell me what the leaving air temperature is.

    How far away from the evap fans can you feel the air flow?

    PHM
    ------




    Quote Originally Posted by primmers View Post
    Im working on a 5 glass door reach in freezer..
    temps were high in the case, its a 502 system
    I had 8/125 psi with a 30 degree box..

    i took one of the condenser fans out to get the head psi up.
    it went to 180 psi..

    anyway, i have a full sight glass, evaporator super heat is 3*

    i have the low psi control set as low as i can set it..

    compressor pumps down to 20+ inches and holds..(manually)

    any ideas??
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  2. #15
    Join Date
    May 2005
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    Thread Starter
    well ill go open it up, maybe somethings in the seat,
    Let's give nukes a chance.

  3. #16
    Join Date
    Jul 2000
    Location
    Guayaquil, EC
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    14,299
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    Quote Originally Posted by primmers View Post
    well ill go open it up, maybe somethings in the seat,
    Check the inlet screen.

  4. #17
    Join Date
    May 2005
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    Thread Starter
    O'tay..
    Let's give nukes a chance.

  5. #18
    Join Date
    Jun 2003
    Location
    Chicago, IL
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    I think I found your superheat problem.

    8 PSI is about -33 degrees. You said the case temp was 30, so assuming a severely starved evaporator, the suction line temp should be near the case temp, which you said was about 30 degrees. This would give you 63 degrees of superheat, but if you forgot the negative, it would calculate to 3 degrees of superheat.

  6. #19
    Join Date
    Jan 2010
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    So primmers , how did you calculate your superheat ?

  7. #20
    Join Date
    May 2005
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    Thread Starter
    I put a probe on the bulb of the TXV, and another on the line coming out of the manifold…my temp device does the rest.(tells me the difference). theres no service valve to hook up a gauge.

    Ill be up there tomorrow, Ill check to see if the TXV has a dirty screen..its a SAE valve..
    Let's give nukes a chance.

  8. #21
    Join Date
    Sep 2002
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    If there is no service valve - how did you perform the pump down test you mentioned in Post # 1 ?

    The test you describe below is deeply flawed. It's only hope of accurate success would be for one probe to be attached to the outlet of the TXV / inlet of the evaporator - with the other probe attached to the outlet of the evaporator / evaporator's suction line.

    PHM
    ------



    Quote Originally Posted by primmers View Post
    I put a probe on the bulb of the TXV, and another on the line coming out of the manifold…my temp device does the rest.(tells me the difference). theres no service valve to hook up a gauge.

    Ill be up there tomorrow, Ill check to see if the TXV has a dirty screen..its a SAE valve..
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  9. #22
    Join Date
    May 2014
    Location
    Bay Area California
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    Quote Originally Posted by primmers View Post
    I put a probe on the bulb of the TXV, and another on the line coming out of the manifold… theres no service valve to hook up a gauge.
    It's really amazing how many different ways I have heard to measure superheat. I really don't get why it is so hard for beginners. Why can't they just read the procedure then follow that ??

    I can only guess that they don't really know what superheat is or means. Which, by extension, would also mean they do not know what subcooling is.

  10. #23
    Join Date
    May 2005
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    Thread Starter
    PHM theres no service valve at the evaporator. I think I did hook up the probes per your instructions..the outlet of the evat at the bulb, and the other to the inlet (at the manifold, this system has two " tubes coming out of the TXV..) I closed the suction service valve at the compressor when I checked the pump down.

    BBeerme, Could you post the instruction you use? thanks.
    Let's give nukes a chance.

  11. #24
    Join Date
    May 2014
    Location
    Bay Area California
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    Quote Originally Posted by primmers View Post
    BBeerme, Could you post the instruction you use? thanks.
    What you will find in this trade is that embracing the terminology will be one of the keys to your success. I had a rookie many years ago that resisted the terminology at every step. It took him months before he realized the error in his ways. Once he started paying attention to the words, he began is journey to becoming a very good tech.

    The definition of superheat is the amount of heat gained after saturation. Saturation is taken from the pressure on your gauge converted to temp. The heat gained is measured as a temp at the outlet of your evaporator. Superheat is the difference between the two.

  12. #25
    Join Date
    Sep 2002
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    So what if there is no service valve at the evaporator? Having it would be a luxury - and certainly not a necessity.

    1. Temperature of the suction line.
    2. Suction pressure converted to temperature
    3. Two subtracted from one is the suction superheat.

    PHM
    ------



    Quote Originally Posted by primmers View Post
    PHM theres no service valve at the evaporator. I think I did hook up the probes per your instructions..the outlet of the evat at the bulb, and the other to the inlet (at the manifold, this system has two " tubes coming out of the TXV..) I closed the suction service valve at the compressor when I checked the pump down.

    BBeerme, Could you post the instruction you use? thanks.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  13. #26
    Join Date
    May 2005
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    Thread Starter
    Heres what Im doing:

    1. Measure the temperature of the suction line at the
    point the bulb is clamped (outlet).
    2. Measure the temperature of one of the distributor
    tubes close to the evaporator coil (inlet).
    3. Subtract the inlet temperature from the outlet
    temperature. The difference is Superheat.
    This method will yield fairly accurate results as long as the pressure
    drop through the evaporator coil is low.


    http://hvac-talk.com/vbb/showthread....heck-superheat


    I must have a communication problem..and Im sorry for that.
    Let's give nukes a chance.

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