Kenmore upright freezer 970-240720 defrost problems

[nitrous2023]

Model Number

970-240720

Brand

Sears Kenmore

Age

More than 10 years

Hi folks, hope someone can help me with a defrost problem.

I have an older stand alone upright kenmore 970 series (Canada)
it has an electronic control.
It works well, cooling to -23C easily.

My problem is that the door (seal appears fine) come ajar an over night, the temperature of the unit raises to 3 or 4C.
When I remove the evaporator cover, the coil is completely iced up, including the defrost element.

I've got continuity on the element, and the thermostat? on the upper left hand side of the evaporator. The thermistor (black rectangle with a screw at the top and red/black wires is not open or shorted, but I don't know what the correct temp/resistance relationship should be to rule in/out this part.

All other aspects of the system work fine - in fact, after manual defrost, it cools down quickly and maintains temp.

I'm suspecting that the system doesn't enter into a defrost cycle, but I don't want to try and find a digital control to replace something I don't need to.

Thanks for any help you folks can give.

Doug

 

[Jake]

Hi Doug,

It works well, cooling to -23C easily.

Since I don't know Celsius. that would be -9.4F which is good.

My problem is that the door (seal appears fine) come ajar an over night, the temperature of the unit raises to 3 or 4C.

How does it come ajar overnight?

Take a photo or video of this happening please, this is extremely rare to ever see happen, unless you have a broken door liner holding the door gasket in place, which is not uncommon after 10 years of use.

970-240720 is Canadian Only, We have no access to parts or schematics for Canadian Only models, unless @Dan O. has one by chance on this model.

 

[nitrous2023]

Hi Jake,
Thanks for replying.

How does it come ajar overnight? Well.... I'm not sure - but when I pull on the door, when the seal is good it's almost like a magnetic seal.... very tight. But occasionally, when I shut the door, it pulls away very easily. When I come back in the AM, it's ajar with the alarm ringing.

Then, the temperature has risen - the evaporator is frozen up solid.... until I pull the evaporator cover off and defrost it with a heat gun. The bi metallic thermostat has continuity as does the element at the bottom of the evaporator.

I don't just want to replace the thermistor.... I just don't know if the defrost is simply not working or if the moisure load has simply overwhelmed its capacity.

Doug

 

[bigbuck]

Sounds like you have good a temperature.Why not use the locking key for the door.Or try raising the front legs of the freezer so the whole freezer is tilted back!

 

[nitrous2023]

thanks Bigbuck!
you wouldn't happen to have the temp/resistance chart for the kenmore thermistor? (if it needs to be replaced, I'd like to fix it)
you know, as a solution - locking the darn thing seems pretty workable
I wonder if I can find the key!
Thanks again,
Doug

 

[bigbuck]

This should be it!

 

[nitrous2023]

Thank you! the part number even indicates availability, here from a CANADIAN source!
You're a lifesaver!

One quick question - it seems to indicate that a failed thermistor will kick out an error code - I'm not getting any such error,
is there an easy/practical way to see if the defrost system is actually working? I understand that every 12hrs, the system should initiate a defrost cycle.

Take care,
Doug
(BTW, I ordered a key on amazon!)

 

[bigbuck]

The codes error codes are only for an open thermistor or shorted thermistor.Most will fail out of range and no error code will appear. Let’s start over here.If the door pops open you will get a big build up of frost.Maybe there is nothing wrong with the defrost circuit! Best to wait for key to make sure the door does not pop open again.Also make sure you defrosted all the frost and secure door for a week or so and then look for frost build up! Fix one thing at a time!

 

[nitrous2023]

Thanks again for your reply.

I'm a little confused here. If I keep the door closed, and there is no frost on the evaporator after a week, will that establish a functional defrost circuit? The freezer will maintain temp (-23C/-9F) without problems. I've never pulled the cover off the evaporator (except when it has clearly frosted up after the door being ajar) but it seems that without opening the door, there should be no introduction of humid air an so, no frost formation.

Would it make sense to pull the controller module from the door and try a thermistor reading? (I don't think that the leads from the thermistor to the control board would be a problem in terms of resistance... or would they)

Is there a way to force the system into a manual defrost cycle? ie so that I can establish that the heating element is functioning? Is it likely that the control board is malfunctioning?

Thanks again, BigBuck
Doug

 

[Jake]

Thanks bigbuck.

How does it come ajar overnight? Well.... I'm not sure - but when I pull on the door, when the seal is good it's almost like a magnetic seal.... very tight. But occasionally, when I shut the door, it pulls away very easily. When I come back in the AM, it's ajar with the alarm ringing.

This is the key event you need to focus on first, the door should not open by-itself. Is the freezer overpacked with items in it, making the door seem shut at times, then re-opens?

Another idea is to raise the front legs so the door closes by-itself with gravity.

I wonder if I can find the key!

Yes, look for the key. If you can't find it, put something in front of the door to keep it closed overnights, its not a good idea to replace any parts till the door continually stays closed to keep condensation from forming into frost/ice.