[tyang54]

We have a Kitchen Aid: KBLA20ELSS00 now a little over 5 years old. It is very clear that the defrost system is not working, within 2 weeks the freezer coils are completely frosted over and only a manual defrost (i.e. unplug the fridge) gets the thing working again.

I have tried to trouble shoot the system based on your advice in here, but I am running out of things to replace. I don't own an ohm meter, so I tried brute force replacing all possible failure parts. So far i have replaced:

Defrost Timer: AP3492964
Defrost Heater: AP4078863
Thermostat kit: AP3475238
Ice Maker Thermostat: AP3135377

It seems that the new heater is still not heating up and defrosting the ice.

Any tips on what else I should be looking at? I will purchase an Ohm meter to check continuity tomorrow, any ideas what i should do after that?

[chlear909]

ok here are some photos of the inside etc.im manual defrosting every 5 days now.it seems to help leaving the cover off as shown.
thanks

[Gene]

chlear909,

One of most common problem is such situation is a bad defrost thermostat (in the left upper corner). Check this part for continuity while it's cold and replace if it's open.

The part number should be marked on the old part. If it's not ,then it suppose to be the temperature mark, like L50-35 or something like that.

Post your findings and I'll help you to find the right replacement part.

Gene.

[chlear909]

thanks Gene,ill replace that part and get back with results,thanks again for this great service

[abadfish66]

Another idea, somthing that I do once in a while is to unplugg the refer, and cut and strip the wires on the defrost thermostat and connect them together (the 2 wires that are part of the machine, not the thermostat) tape the ends. now plug the power cord in, turn the defrost timer to defrost, and see if heater comes on. If it does, your defrost thermostat is bad, if your heater does not come on, your heater is bad. Maybe this can help those that do not have a meter, or know how to use one.

[tyang54]

I presume you mean to bypass this part - it was clipped to the refrigeration coil. and seemed to be in between the heating element and the rest of the circuit.

[abadfish66]

That is correct

[tyang54]

I am still a little fuzzy how the freezer knows when to defrost/stop defrosting. It seems that the defrost timer closes the circuit to begin defrosting once every x hours. At that point the thermostat (above) provides a second check to see if the freezer temperature is below a certain point (35F?). If it is, then the fridge needs defrosting and the circuit closes, sending power to the heating element which heats up and starts defrosting the cooling coil.

So how does it know when to stop defrosting? Is it as simple as the thermostat temperature rising above the set point? And then, because the thermostat is clipped to the top of the cooling coil, and the heating element is at the bottom of the heating element, the thermostat should not turn off until all of the coil is properly defrosted?

In essence the thermostat just opens and closes at a specific temperature (35F?) - My question is essentially how do I test continuity on the thermostat. Can i just cool it below 35F, or how does the thermostat sense ice.

[abadfish66]

The thermostat is in a closed state when below a certain temp, and opens up when the evap has reached around 70 degrees during the defrost cycle. So the thermostat must be cold enough to test it in a closed position, and room temp to test in open position

[tyang54]

So I got the meter and the heating element tests fine (about 20 Ohms) the thermostat shows continuity when it is cold, open circuit when it warms up. The only thing I can think of now is that for some reason there is no current going to the heating element when it is in defrost mode. What is the correct way to test this - I don't know if there is any reason why the wiring would go bad, or if I can check if there is a bad contact somewhere...