Sub-Zero 642/S - Freezer too cold

[brk]

Freezer temp set to "0".  Temperature display is "-14".  Units are correct.  Ice cream is frozen rock hard, which is how the problem was identified.

Where to start?

[brk]

Found a wiring diagram.  Unplugged the purple wire from the control board, the compressor on the freezer stopped immediately.

So, I assume it's the control board?

Based on model number / serial number, do I have a 642, 642-2, or 642-3?

 

 

[Hiroshi]

First thing you would want to do is test the resistance of the thermistor in the freezer compartment, unplugging a random wire doesn't prove anything from a diagnostic standpoint...There should be literature in a manila envelope somewhere in the machine compartment of the unit, you can also call Sub-Zero and they will help you as their tech-line is very open. The computer controls are extremely reliable in these fridges, so I would do extra homework before buying a new part...

Sub Zero goes entirely upon serial number and the parts are only available through specific sources... Try this page:  http://www.midwestdistributing.com/Store/OpenPages/ManualPage.aspx?PageTitle=MANUALS

[brk]

Thanks. I did find a wiring diagram and the purple wire is the one that goes to the freezer compressor. I should've mentioned why I selected the purple wire 

From the parts list, it looks like there is a relay on the compressor. I've found some reports that relay sometimes sticks. If that relay was stuck, a disconnect from the control board would still leave the compressor running?

 I'm also assuming it's not the thermistor. Because the temperature display for the freezer section appears correct. 

 Now the interesting part. After unplugging the unit to plug the purple wire back into the control board, everything is working properly again.

 Guess I'll just wait until it stops working one more time .

[Hiroshi]

Hmmm, weird... I am uncertain how a PTC relay could "stick."

I sure hope they didn't switch to the fake PTC electronic start relays...

To answer the question though, NO, if you remove L1 power from the compressor it cannot stay running.

 

Edited December 7, 2016 by Hiroshi

[brk]

The freezer went into super-freeze mode again.  Identified by rock hard ice cream.  Display read -15 on the freezer side.

This time I hit the "on/off" button on the control panel.  Lights, display, and fans went off.  However...  the compressor kept running???

I have it plugged into a power monitor - it was pulling just over 1A.  With the system "off".

I then pulled the plug from the wall.  All stopped (thank goodness).  Waited a few minutes, plugged back in.  Now it's headed back towards the proper temp.

Suggestions?  It's happened about once per year +/-.

[Budget Appliance Repair]

Sounds like you have an intermittent sticking relay for the freezer compressor on the main board.

New main board would most likely take care of your problem, but I'm not really familiar with Sub-Zero, (some of the older - I think 500 series used time delay relays for the compressors).

[brk]

Thanks.  Guess I need to decide if I put a few hundred $$ into a 19 year old fridge for an intermittent problem.

[mutantfrog]

On 9/9/2019 at 9:43 PM, brk said:

The freezer went into super-freeze mode again.  Identified by rock hard ice cream.  Display read -15 on the freezer side.

This time I hit the "on/off" button on the control panel.  Lights, display, and fans went off.  However...  the compressor kept running???

I have it plugged into a power monitor - it was pulling just over 1A.  With the system "off".

I then pulled the plug from the wall.  All stopped (thank goodness).  Waited a few minutes, plugged back in.  Now it's headed back towards the proper temp.

Suggestions?  It's happened about once per year +/-.

I had the same symptoms on a Sub-Zero 700TC, and fixed it the same way. Except I went to the fuse box to turn it off completely instead of unplugging from the wall. Thank you!

[brk]

I ended up replacing the main board. I was experiencing several strange symptoms. 
 

the deep freeze hasn’t returned. But it was so infrequent I wouldn’t know if it is really solved.