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  1. #1

    Is this normal?: True T-72F evap coil 250 deg F during defrost?

    I have a True T-72F 3-Door freezer that cools well normally, but when the defrost timer kicks in (set at 10 minutes for now as a result of this issue) it never stops heating until the entire time is up, even with no frost build up. I tested it with an IR temp gun while sitting inside the unit during the defrost cycle so I could monitor the evap coil temp throughout. It was below what my gun can read at the beginning of the cycle (-5F) and gradually rose until it was 200+F over the entire coil by the end of the 10 minute cycle and 250F in some spots. The inside air was up to about 80F by then and there was steam condensing on the cieling. It felt more like an oven than a freezer. Is this normal? It seems like an awful lot of wasted energy to continue to heat so long (wasted energy in unnecessary heating and the energy to cool that back down after).

    There are two wires visible in the clear drain tube coming from the back of the evaporator casing. Are these supposed to be coming from a defrost termination sensor? If so, what temp should the evap coil be getting to before the sensor clicks?

    If I need a new sensor/switch is it reasonable to do myself or do I need to have a contractor do it? (I am a mechanical engineer with good electrical experience, but I'm not an experienced HVAC guy really). This is a freezer that my wife used in her smoothie shop that I plan on selling.

    Thanks in advance for any help.

  2. #2
    Join Date
    Feb 2010
    Location
    NE Alabama
    Posts
    301
    Call a refrigeration service.

  3. #3
    Join Date
    Dec 2011
    Location
    Michigan
    Posts
    119
    You need a new terminator. The wire in the drain line are for the drain line heater.

    Sent from my amazing 4G device

  4. #4
    Join Date
    Oct 2003
    Location
    las vegas
    Posts
    1,505
    call in a refer man before you end up having big problems.

  5. #5
    Join Date
    Apr 2007
    Location
    Loris SC
    Posts
    208
    I'd say defrost termination also, its a 3 wire devise to terminate defrost then delay the fans from coming until the coil cools down some. I believe in a True box its a Flush mount style with a red, black, and brown wires.

  6. #6
    Join Date
    Oct 2011
    Location
    Chicagoland Area
    Posts
    4,615
    It's more than a termination problem. Sounds like more than one switch is bypassed. The heater limit should have opened if termination failed. Put pizza dough in it and use it as a proofer.
    Officially, Down for the count

    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

    I know enough to know, I don't know enough
    Liberalism-Ideas so good they mandate them

  7. #7
    Join Date
    Mar 2007
    Location
    wedged in freezer shelf
    Posts
    6,727
    How do you shoot a whole evap with I/R without taking off the cover?
    How do you know you are not picking up direct heat off the electric heater with I/R?
    The heaters get HOT! The cover keeps the heat up top to defrost the coil and terminate defrost.
    A 3 door freezer does use a lot of energy and a 3 door is a big unit for most smoothie shops I've been in
    Usually no room to even open the doors
    “If You Can Dodge A Wrench You Can Dodge A Ball”

  8. #8
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,356
    Quote Originally Posted by 2sac View Post
    It's more than a termination problem. Sounds like more than one switch is bypassed. The heater limit should have opened if termination failed. Put pizza dough in it and use it as a proofer.
    True may have revised their design since, but most of the 3-door freezers I've worked on had no limit tstat:



    (NOTE: I took this pic because this GDM-72F wiring diagram was wrong. It doesn't indicate the 230V supply to the compressor properly...but it still shows no heater limit.)

  9. #9
    Join Date
    Oct 2011
    Location
    Chicagoland Area
    Posts
    4,615
    icemeister, you may be correct although True lists a part#800360 as a high temp cut out. I can't find a pic or disription. Also unable to find wiring diagram online. I seem to recall (3) seperate 2 wire switches or (2) 2 wire and a 3 wire, but it's been awhile. If I'm not mistaken, there are 2 switches mounted to the coil at the right front, and a 3rd mounted to the top of the cabinet near the coil on the left.
    Or I could just be an idiot
    Officially, Down for the count

    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

    I know enough to know, I don't know enough
    Liberalism-Ideas so good they mandate them

  10. #10
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,356
    Quote Originally Posted by 2sac View Post
    icemeister, you may be correct although True lists a part#800360 as a high temp cut out. I can't find a pic or disription. Also unable to find wiring diagram online. I seem to recall (3) seperate 2 wire switches or (2) 2 wire and a 3 wire, but it's been awhile. If I'm not mistaken, there are 2 switches mounted to the coil at the right front, and a 3rd mounted to the top of the cabinet near the coil on the left.
    Or I could just be an idiot
    You're no idiot, so not to worry my friend.

    True seems to quietly change stuff all the time. I think this is why they never publish wiring diagrams. If you need one, they'll email it to you...but you must have the serial number.

  11. #11
    Join Date
    Mar 2006
    Posts
    1,032
    its a part of trues new line, its part reach in cooler and part hold cabinet
    You can't kiss death without it kissing you back. Death is a passionate kisser.


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