Subzero 642 - temp readout showing 35, fridge actually 50

[brk]

July 2001 model...

Any hints?  I looked at the wiring diagram and see there is a fridge temp and evap temp sensor.  Not sure where it would be located?

Display shows 35

IR thermometer shows between 50 around the bottom, 58 around top inside fridge compartment.

It seams to me the options are -

  - Temp sensor(s) are bad

  - Temp sensor(s) are encased in ice, due to low charge?  (not sure if this is possible)

  - Control board is bad

 

I had a too cold problem this past december that cleared up on power cycling...

 

 

[16345Ed]

Refrigerator Compartment Thermistor (Models 601R, 611, 632, 642, 650, 690)

The refrigerator compartment thermistor is located behind the evaporator cover, and attached to the wall just above the evaporator. To access and remove the refrigerator compartment thermistor, the light diffuser and evaporator cover must be removed first. Now dis- connect the thermistor wire leads from the wire har- ness, and extract the screw which secures the thermis- tor to the rear wall. 

Refrigerator Evaporator Thermistor (Models 601R, 611, 632, 642, 650, 690)

NOTE: Evaporator fins are sharp and could cause minor personal injury.

The refrigerator evaporator thermistor is attached to the center of the right evaporator bracket. To access and remove the refrigerator evaporator thermistor, the light diffuser and evaporator cover must be removed first. Now disconnect the thermistor wire leads from the wire harness, and extract the screw which secures the ther- mistor to the right evaporator bracket. 

[Hiroshi]

Control boards on these machines are some of the most reliable I have ever seen... the thermistor being out-of-spec is the most likely scenario in this case. 

I would also use a physical thermometer in one of the food products (jelly, jam, mustard etc.) to check the actual food temps, IR thermometers can have major variance according to what surface they are aimed at- so, it never hurts to use Hi and Low tech methods to prove a theory!

The thermistors are all the same part #, so if you put them in a glass of ice water or keep them in the same temp. area, they should read read equal resistance.

 

[northeastappliance]

Also check the molex connecter for the termister. I've seen them corrode and that could cause a false reading. 

[brk]

 

Thanks all!  I found the thermistors!

in the process of disconnecting them to test resistance I wiggled the connectors and the temp display immediately jumped up to 60 degrees. Shortly thereafter the compressor kicked on.

I cleaned the contacts the best I could. I see the replacements have different connectors, so I ordered a set.  I'll happily keep my main computer board!  I also vacuumed the coils on the top while I had the grill off.

Agree on the IR thermometer concern.  I also tested with an instant read in my water pitcher, the one I poured the glass of water that I noticed was warmer than usual.

Thanks again!

[northeastappliance]

If I remember correctly, the new thermistors from sub z come with butt connectors with heat shrink on them. You are supposed to cut out the molex connector and use the butt connectors. 

[AccApp]

On 2/27/2017 at 7:51 PM, northeastappliance said:

If I remember correctly, the new thermistors from sub z come with butt connectors with heat shrink on them. You are supposed to cut out the molex connector and use the butt connectors. 

Absolutely true, also worth trying is to simply cut out the connectors and splice the wires with any reliable method: butt connectors, wire nuts, etc.