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  1. #1

    Defrost Termination question

    I was working on a walk in freezer today that had two bad condensor fan motors which I replaced...
    I started up the unit and was waiting for the evap fans to kick on ( waited about 30 minutes )
    Felt the evap. getting cold but the fans didn't kick on.
    I jumped out the Defrost Termination control and the fans started... so i went and picked up a new defrost termination control>
    When I got back the freezer was running @ 30 degrees> i put in the new control and started it up> same problem. fans did not start...

    really weird senerio.. I need some opinions. would really be helpful. thx!

  2. #2
    Join Date
    Oct 2011
    Location
    Chicagoland Area
    Posts
    4,618
    It's doing exactly what it's supposed to do. 30 minutes seems excessive. Sounds like you may have additional problems. I woud be checking the charge, and the metering device as well as compressor efficiency. Why were the motors bad? and did you clean the coil while you had them out?
    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

  3. #3
    Join Date
    Apr 2003
    Location
    Maple Grove, MN
    Posts
    1,293
    Was the coil frozen up from running without the fans? Did the compressor slug itself to death and bust its valves? What are your pressures and your evaporator superheat?

  4. #4
    Join Date
    May 2004
    Location
    Salt Lake City/Tooele
    Posts
    2,486
    Probably the defrost termination and fan delay switch. As 2sac stated, it is either doing what it is suppose to be doing and not closing to energize fans until evap coil temp drops low enough, or it is faulty and sticking and not energizing the fans. Time to investigate just a bit more.

  5. #5
    Join Date
    Sep 2010
    Location
    Western, MO
    Posts
    871
    If the evap fans aren't running the DTT is the first thing I check. I had a tech order fan motors without checking to see how it got it's power and neutral.

    jim
    Common sense isn't very common anymore.

  6. #6
    They had a power outage yesterday. Ive never seen two die at once tho. Charge is good.. little high head washed n blew out coil. Running at 285 n 32. Ill have to check out mire tmrw thx for the help

  7. #7
    Join Date
    Oct 2011
    Location
    Chicagoland Area
    Posts
    4,618
    Betcha got a ZP charge on the powerhead. Should be good tomorrow.
    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

  8. #8
    Join Date
    Jul 2012
    Location
    Western KY
    Posts
    1,221
    Hot box and high ambient?
    May take a bit to pull down enough to make fan Circut. Should pull down at a steady clip though. If coil temp is not dropping steady your problem is elsewhere, as pointed out earlier. Charge, TXV, headmaster, comp valves, etc.

  9. #9
    Join Date
    Oct 2002
    Posts
    1,306
    Had a freezer that gave me fits.

    Defrost heater was switched on the neutral leg. Intermittant grounded would bring the heater on with defrost stat open-sometimes. Usually after I left.

    Acted the same way. Charge right, but slow pulldown.

    Took forever to finally catch the defrost heater on while trying to cool.

  10. #10
    Join Date
    Jan 2008
    Location
    michigan
    Posts
    1,145
    I had a problem once, similar in nature, on a three door display freezer. Changed the fan delay switch and unit took off. Next day get a call, not working again. Arrive on site, it is working fine. Check charge, SH etc., all good. Put unit in defrost, comes out of defrost and all works fine. Hmmmm. Did that multiple times. Even emptied out the contents, let box warm up and tried it again, all good. Next day, same problem. Only this time when I arrive, fans aren't running. Start checking power and discovered no power to fan delay switch. Turns out that the wire that ran from the terminal strip, throught the box, and to the FD switch had a "break" in it somewhere, and would send power most times but occassionally would "break". Replaced that wire and all was good. Drove me nuts.

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