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Thread: SubZero 550 Freezer won't come on

  1. #1
    Join Date
    Apr 2013
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    dfw
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    Default SubZero 550 Freezer won't come on

    Model Number: 550
    Brand: Sub Zero
    Age: More than 10 years

    The freezer on our subzero keeps getting stuck off. If I check voltage across the thermostat wires at the defrost timer, I get around 3 to 6 volts, if that means anything. When I unplug wires from the thermostat to test, I get the full 120, and once I plug it back in, everything's fine. I've already replaced the thermostat and it did the same thing a week later.

    This time, it happened because our freezer was freezing closed and my wife turned the thermostat down to let it thaw and it wouldn't come back up. I think the last two times it has happened it was when we were out for several days.

    The last time I messed with it, I was trying to figure out a why to get it working without taking the thermostat back apart. I had the defrost timer disconnected and the breaker off for a while. When I put everything back together, the refrigerator compressor kicked in, but I heard several clicks, maybe a minute apart, for several minutes, before it finally did. I don't know if that is normal either, but the freezer compressor didn't kick on until the refrigerator compressor did.

    Is there something I'm missing, or do you think my replacement thermostat is bad, too?

  2. #2
    Join Date
    Apr 2013
    Location
    United States
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    Default

    Sounds like a defrost issue more than anything. When you have a defrost issue the evaporator coil on the ceiling of the freezer turns into a big block of ice. This freezes the door shut. Since the fan isn't spinning and the thermostat is not seated on the coil, it never reaches its temperature in order to shut off the freezer compressor, overworking it until it practically destroys it, or shuts it off on overload.

    what you should do.

    turn off the freezer all together for 48 hours and let thaw completely.

    check your timer, is the wheel spinning in there? If not, replace your timer. You probably should anyway at this age.

    If it is not the timer I would then open up the unit and check the terminator switch located in the freezer compartment, on the ceiling.

    You may require a new Sub Zero heater element that goes down the freezer drain, it was not introduced until later models of the 550.

    if you have a problem, call me and ill get back to you. link is below.

    -Joe B
    Sub Zero Repair Co.

  3. #3
    Join Date
    Jun 2013
    Location
    Tennessee
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    Default

    I have a similar problem. My SubZero 550 will run for 2 or 3 weeks then starts warming up. Sometimes I can get it going by manually putting it into defrost by turning the timer. When I do that , it comes out of defrost automatically and will run for a while. Often, I have to shut off the freezer and let it defrost to get it going. The wheel on the defrost timer is spinning, and as I said it does come out of defrost automatically. I don't quite understand what the function of the terminator switch is. Does the timer initiate defrost and the terminator switch end it. If the switch is not working does defrost terminate too early and thus cause ice to build up on the coil?

  4. #4
    Join Date
    Oct 2004
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    Ontario, Canada
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    Default

    Hi,

    I don't quite understand what the function of the terminator switch is.
    Shuts off the power to the heater once a predetermined temp has been reached in the evaporator area.

    Does the timer initiate defrost and the terminator switch end it.
    Yes, no.
    LINK> Refrigerator Defrost Cycle | Appliance Aid

    If the switch is not working does defrost terminate too early and thus cause ice to build up on the coil?
    Ice or frost?
    *If* the defrost heater is working, changing the defrost timer and defrost thermostat is normally the best repair.

    Defrost thermostat
    Derfost timer

    jeff.
    http://www.applianceaid.com/
    Appliance Repair Aid
    Yeah I've got O.C.D.....Old, Cranky and Dangerous.

  5. #5
    Join Date
    Apr 2013
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    United States
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    Default

    After keeping unit off for two days and letting freezer completely defrost I would take these steps to diagnose problem as consumer.

    Turn unit on, let it get down to temp.

    Assuming the defrost timer is working, if you manually engage timer into defrost and heaters don't go on its the terminator switch or the heaters, (it is almost always the terminator switch)

    Do this as well.

    1. If your freezer fan spinning when the top basket is engaging switch in the back left of freezer ?

    2. Yes? Is the basket loose, coming off the track? Is it possible It is not engaging switch when you close door once in a while? If the fan is not spinning it will eventually cause the problem you describe .

    3. It's hard to diagnose without looking at frost or ice pattern on coil but you may want to preemptively replace timer, they are cheap and at this age shoul d be replaced anyway on a subzero 550.

    4. Is there ice buildup on the right track of freezer bin causing the door to stick shut? There Is a drain on the upper right hand side that notoriously clogs and needs an aux defrost heater installed. More than likely wouldn't cause fluctuation in temp but worth mentioning.

    5. Do what i listed below and if problem persists replace terminator switch. It is clipped onto the evap coil in freezer. You have to remove all screws while laying on your back, it's a pain and you may want to hire technician who knows sub zero for repair.

    6. there are a slew of different things that could also go wrong like corroded or burnt out contacts . It's always good to have a professional diagnose these things but it is often a simple fix. Good luck

    John @
    http://certifiedsubzero.com/
    Last edited by john b; June 8th, 2013 at 08:13 AM.

  6. #6
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    Jun 2013
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    Tennessee
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    I was attempting to replace the freezer defrost terminator on a Subzero 550. I had trouble locating it but I think I finally found it underneath the fan cover. It was just laying in there. It has a clip on it. Is that supposed to be attached to something like a return bend? Could that be why the freezer was not defrosting well?

  7. #7
    Join Date
    Oct 2004
    Location
    Ontario, Canada
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    Yes, should normally be clipped to the evaporator coil.

    jeff.
    http://www.applianceaid.com/
    Appliance Repair Aid
    Yeah I've got O.C.D.....Old, Cranky and Dangerous.

  8. #8
    Join Date
    Jun 2013
    Location
    Tennessee
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    Default

    Thanks for all your advice on my subzero 550 freezer. As I said, it ran fine for a while, then would start warming up. I think the problem was that defrost was terminating early before the evaporator was completely defrosted. Eventually it would ice over blocking air flow. I clipped the defrost terminator switch to a return bend on the evaporator. Hopefully it will run well now.

    Lately I have been having trouble with the refrigerator also. It is gradually warming up even though the compressor runs all the time. This suggests that it is low on refrigerant. I wanted to confirm that with pressure measurements but have run into a problem. There seems to be only three pressure taps for both compressors. Each compressor has a tubing stub coming from the compressor housing ending in a Shrader valve. There is a third tap coming from two small volumes in the front center of the compressor compartment. I can't figure out what these go to. How do I check the system pressures to see if it is low on freon?

  9. #9
    Join Date
    Oct 2004
    Location
    Ontario, Canada
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    Default

    Each compressor has a tubing stub coming from the compressor housing ending in a Shrader valve.
    That would be it....the fresh food section compressor.

    Should be around 15 pounds back pressure.

    jeff.
    http://www.applianceaid.com/
    Appliance Repair Aid
    Yeah I've got O.C.D.....Old, Cranky and Dangerous.

  10. #10
    Join Date
    Jun 2013
    Location
    Tennessee
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    Default

    I thought I would let you folks know how my freezer repair worked out. I clipped the terminator switch to the evaporator return bend seven weeks ago. It is still working well with no problems. I think it is safe to assume that the problem is solved. Thanks for all your help.

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