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  1. #1
    Join Date
    Jun 2009
    Posts
    92

    Thermostat bulb in supply air

    Thermostat sensor like a A19 mounted so the supply air effects its operation.

    I have come across this a few times and I don't like it. For a while I thought someone did not know the direction of air flow in a reach-in but in a walk in there is no way.

    Is there any reason to do this?

    My thinking is you want the air in the box to be in the safe zone so control that the air entering the evaporator or if you want the coil temp directly

    what do you think

  2. #2
    Join Date
    Mar 2009
    Location
    Mid-Mo
    Posts
    3,429
    I've been using a 1/2 emt strap to secure the wire and let the sensor hang down in the air stream of the return. Avoid mounting the sensor on the evaporator, wall, or anything else for that matter.

  3. #3
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    24,998
    In refrigerated display cases, this is a very common control scheme.

    In walk-in cooler/freezer application, it doesn't work so well.

  4. #4
    Join Date
    Jun 2009
    Posts
    92
    Yes I agree but what are people thinking when they mount it in the supply

  5. #5
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    24,998
    What I meant to say is that a thermostat sensing bulb, located in the supply air, is a common control scheme on reach-in cases.

    Not on walk-ins which, as you said, want the sensing bulb in the return for a better average temperature.

  6. #6
    Join Date
    Apr 2012
    Posts
    15
    Reach in coolers and open refrigerated display cases are often controlled like that. They work fine, you just set them lower than for the return. If something goes wrong, like your compressor gets old and tired, then they won't shut off because discharge temp doesn't get low enough. I often replace that type of control in a reach in cooler with an A12-700 that runs on the return, gives them a few more years of trouble free operation.

  7. #7
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Quote Originally Posted by richvacr View Post
    Yes I agree but what are people thinking when they mount it in the supply
    Ahh, you are making the mistake of assuming that those people were thinking.

    Life is much simpler if you operate under the assumption that everyone else that worked on it before you was an idiot.
    If more government is the answer, then it's a really stupid question.

  8. #8
    Join Date
    Jun 2003
    Location
    Chicago, IL
    Posts
    4,198
    putting the sensor in the supply offers a half-@$$ed form of automatic defrost

    As the coil freezes up the airflow through the coil drops and the discharge temperature drops, shutting off the stat even if the case is still warm. once the compressor shuts off the coil continues to supply cold air due to the melting ice. Once most of the ice is melted, discharge air warms up and the stat kicks back in.

  9. #9
    Join Date
    Jul 2008
    Location
    hearth planet
    Posts
    86
    The reason for a temp bulb installed in the air discharge is to prevent iced up coils when a lot of air infiltration is present such as open cases, prep rooms and heavy traffic w/i boxes.

  10. #10
    Join Date
    Sep 2007
    Location
    NH
    Posts
    1,111
    My vote is for supply air to keep the best product temp... Why do I care what the temp is in the return of the case???

    Doesn't work well in the return especially on open cases with stores with poor AC in the summer.

    Walk In coolers and freezers they always go on the return

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