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Thread: evaporator td

  1. #1
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    evaporator td

    what is the proper way to check ? i thought it was to check temp at incoming evap and outgoing but the guy i am working with said it was to shop so i dont want tyo check at supply and return air temp. i am new and this is my first shop and i am training with this guy but i think he is wrong. can you guys help me?

  2. #2
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    Box temp minus boiling point of ref being checked.
    I.E. Air temp minus PT
    404a
    Box temp at 32
    Suction pressure @ 60psig (22 deg)
    10deg td

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  3. #3
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    Evaporators are designed to run at a certain TD depending on its design and application. What are you trying to accomplish by taking a TD of a refrigeration evap coil? You should be able to diagnose refrigeration problems thru other means. Verify the coil is clean and fans are running properly.
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  4. #4
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    Quote Originally Posted by 2sac View Post
    Evaporators are designed to run at a certain TD depending on its design and application. What are you trying to accomplish by taking a TD of a refrigeration evap coil? You should be able to diagnose refrigeration problems thru other means. Verify the coil is clean and fans are running properly.
    this was a procedure for a pm

  5. #5
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    it was a way of knowing if the unit was operating correctly ?

  6. #6
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    what is the correct way of checking this ?

  7. #7
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    the coil was clean and fans were running proper. this weas on an ac roof top unit. does that make a difference ?

  8. #8
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    i also wondered why i would need a td on an evap. but i am new and dont want to rock the boat.

  9. #9
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    Quote Originally Posted by royd2 View Post
    the coil was clean and fans were running proper. this weas on an ac roof top unit. does that make a difference ?
    This thread is posted in the refrigeration section, not commercial a/c.
    An evap TD is more beneficial in an a/c package unit for troubleshooting. Take a temp at the return and suply near the evap coil by drilling a small hole. A tek screw will work with most probes. Not a big deal. Somewhere between 15-25 degrees is usually normal.
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  10. #10
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    Quote Originally Posted by 2sac View Post
    This thread is posted in the refrigeration section, not commercial a/c.
    An evap TD is more beneficial in an a/c package unit for troubleshooting. Take a temp at the return and suply near the evap coil by drilling a small hole. A tek screw will work with most probes. Not a big deal. Somewhere between 15-25 degrees is usually normal.
    This would be more of a Delta-T

    A TD is used when you are taking the temperature difference between 2 different mediums such as...

    (Return Air - SST = Evaporator TD) RA - SST = TD

    or

    (SCT - Ambient = Condenser TD)

    A Delta-T is when you are measuring the temperature difference between the same medium, such as...

    (Return Air - Supply Air = A/C Delta-T) RA - SA = dT

    or

    (Filter Drier Inlet - Filter Drier Outlet = Filter Drier Delta-T)

  11. #11
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    2sac thanks for the help also phase loss it makes much better sense now. and we were doing the pm on a lennox rooftop unit. sorry i posted this in the refrigeration section but we work on refrigeration hvac and hot side, so sometimes i forget some things should be in another section. thanks you guys are great

  12. #12
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    Quote Originally Posted by royd2 View Post
    2sac thanks for the help also phase loss it makes much better sense now. and we were doing the pm on a lennox rooftop unit. sorry i posted this in the refrigeration section but we work on refrigeration hvac and hot side, so sometimes i forget some things should be in another section. thanks you guys are great
    It is important to know the evap TD as described by phase loss when checking and or adjusting super heat on expansion valves. The method applies to all evaps, water , air . Airconditioning and refrigeration to maximise evaporator operation.

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