596.65232404 Kenmore fridge defrost heater?

[GinaM]

I have been working on this fridge. Frosts over the in the freezer.  Hot fridge.  Defrost it, replaced what seemed to be a faulty thermostat (by continuity testing in an ice bath. and it works for a a few months and does it again.   Now it seems I’m trying to figure out if the heater works.  Tested it and got 0 ohms.  The tech material under the fridge says that it should be 30 +/- 5%.  I know if it read high it is broken, but what about reading low?  Is it broken? 

Tried running the forced defrost mode and no heat.  But that could be anything from the board on down right?    

[Vance R]

14 hours ago, GinaM said:

 I know if it read high it is broken, but what about reading low?  Is it broken? 

Depends on how you measured it. The heater has to be unhook, you could be reading something else in parallel with it. Please do not use continuity for these tests, use resistance! You can measure from the board.  Remove connector J1,  Measure resistance from pin 5  br wire to pin 3 or wire - if it is 56k ohms bi-metal is open, if it is 0 ohms bi-metal is closed. Next measure pin 3 or wire to pin 1 wh wire - this should be 30 ohms.  If any of these measurement are not correct you will have to pull evap cover and check at the components.

Bi-metal explanation - they don't show it in the wiring diagram or talk about it in the specs. Inside the bi-metal is 56k ohm resistor placed across the contacts. That way when you measure you know if the bi-metal contact are open or closed. Also help if measure from the board you also know if your wires are good. 

This is a jazz board and they are notorious for not going into defrost on their own. They will go into defrost in the diag mode.

14 hours ago, GinaM said:

Tried running the forced defrost mode and no heat.  But that could be anything from the board on down right?

Yup, the above tests should help find the problem and correct it. From your statement you'll probably need to replace board also. 

[GinaM]

Thanks. I did measure it disconnected but will try your suggestions too

[GinaM]

So Vance,  Thanks again for your help.  From the board the thermostat reads zero ohms.  The heater also reads 0 ohms.  As it does when it is disconnected from the circuit.  So should I replace the heater and if that doesn't work then recheck the thermostat since it will be plenty warm when I have to defrost the refrigerator again.  If the thermostat is good, and the replacement heater is good then I have to replace the board? 

[GinaM]

(since I already checked the heater itself and it reads O ohms too)  The thermostat is new but not all new parts are good.

 

 

[Vance R]

The bi-metal should open at about 45 degrees.  Odd the heater is 0 ohms, it could happen but i've never seen that failure. Usually heater increase in resistance or open completely.

The board has a know failure where it will not go into defrost by itself. Defrost can be force by the test mode. Once you get the defrost heater circuit working correctly you can just wait and if in 2 to 4 weeks the defrost issue comes back replace the board at that time.

[Slav]

On 5/3/2020 at 9:12 PM, Vance R said:

Odd the heater is 0 ohms

It's probably a cheap multimeter that doesn't have the OL symbol. So any open circuit will read 0 ohms.