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My coil was iced up. I defrosted it. While I was in there I took a resistance reading on the defrost heater, it read 35 ohms. I am assuming it is good. Now what controls the heater and how can I check if it needs replacing.

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If it's a glass heater you can look at it,if it's all black change it out,i've checked heaters that read good but it still needed to be replaced,like i said pull it out and do a visual look at it,if your machine has a timer,advance the timer by spinning the knob on the timer until you hear a click,when it clicks it's in defrost,if the heater doesn't come on check the defrost thermostat on top of the coil,depending on your machine,some have plug in connectors on the can unplug the thermostat and send power dirrectly to the heater bypassing the thermostat,if the heater comes on then the thermostat is bad,if you don't have the plug in connectors you can cut the wires and bypass the thermostat and see if the heater comes onyou'll have to cut them anyway and then wire nut them together if the thermostat's bad , also you can look at the thermostat,if it's bulgging on the top it's bad,also when you look at the heater,if it's black inside the glass change the heater and the thermostat have to melt out all the ice off the coil before you close up the back wall,if there's a board in your machine there's a white sensor on the top coil,it looks like a bullet, i think the part number is wr55x10025,the older sensors are white but they have a black ring around them near the end of the bullet part,the new sensors are all white, it's a good idea to change that out also.let me know what you find,next time send the model number

Posted on Oct 10, 2010


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There a number of reasons that ice forms on the evaporator coil. One is no air flow or not enough air flow over the coil. Another reason could be the unit is not going into defrost. There will be some ice on evap coil most of the time, but the defrost cycle should remove the ice. If there is not enough air flow across the coil to take away the cold, the coil will build up ice. I would check the defrost cycle and make sure there is not an obstruction in the circulating fan system. On the older refrigerators you could turn the defrost timer to defrost, but the newer models have circuit boards, and I am not sure how to force the defrost.

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when the defrost terminator has gone out and u get ice build up? u can check the terminator with a multi meter for continuity but do not check at room temperature. stick the terminator in cup of ice water for 20 minutes then check it for continuity, should be closed when cold and open at room temperature.
May also need to check the defrost timer, u can get by and test manually by placing a small screw driver into the tiny slot or hole underneath the timer and turn slowly clockwise till u hear 1 click. this will engage ur defrost cycle in about 15 minutes u should be able to come back and feel the heat in freezer as it melts the ice providing ur terminator is not bad?
Another way to test it is with a multi meter. Remove timer it from fridge and you will see 4 prongs numbered 2,1,4,3 in that order. Place ur meter prong on prong 1 & 3 (if your fridge has a capacitor wired in series with the windings, then u check for micro fares rather than OHMS) If u cannot confirm this test, still try the next.
Take ur meter prong and connect to prong 1 & 4, it should read resistance or ohms ( closed) now remove prongs and place on prong 1 & 2, this should now read infinity or open (no ohms) now take a small screwdriver place it in the tiny hole or slot under the timer. Turn it clockwise slowly till u hear 1 click. Now ur 1& 2 should read closed ( showing ohms or resistance) now place meter prongs on 1 & 4 and you it should now show open ( or no resistance - no ohms) this is how u know ur timer is good, Remember when testing for ohms ADJUST meter to use a high ohms rating in the thousands as the resistance is very high in OHMS. And adjusting to low ohms rating may give a false reading or not show the proper resistance..

Another item to check with a meter is the heating element itself. Located under the evaporator coils. It should show continuity or resistance OHMS WHEN TESTED AT BOTH ENDS OF THE PRONGS .

Lastly check the cold control thermostat with a meter for both OHMS and volts ( VOLTS is a live test with fridge plugged in so be careful) It must show 110 volts. An open or thermostat that reads infinity will not allow the proper cooling and defrosting cycles to operate and may in fact stop anything from happening as if there is no power to the unit?

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More than likely if your fridge has a bi metal, or a defrost timer, its one of those two issues. Leaning more towards the bi metal. If the bi metal is encased in ice and is reading more than 0 ohms its your bi metal. (small round sick that sits on the tubing) Your heater should be reading around 25 ohms or something like that. it should be fine. If it does not have a bi metal it works on a thermistor and then you more than likely have a electrical control board issue that not forcing the fridge into defrost. Lmk if you need more help!

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Good day,
The defrost system is made up of 3 parts, including the timer.
In addition there is the defrost thermostat, and the main heater.
The item most often to fail is the defrost thermostat.
It is located on the top of the cooling coil your tech defrosted.
It looks something like this.f3dea89.jpg

In addition the main could fail could fail, and is located on the bottom of the same coil. It can be tested with an ohm meter, nd should give a reading of no higher than 35 ohms.
The thermostat can be tested as well, and should read zero ohms. However, it can only be tested if its temperature is not allowed to rise above 20 degrees.

As well, Whirlpool timers have 2 separate ways of being wired into the plug. Same timer, just a case of getting the flying lead onto the right terminal. VERY IMPORTANT.

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Good day,
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You can access both by removing the back panel in the freezer compartment. The thermostat can be checked with a vom meter but must be below 25 degrees to test properly. It should read zero ohms of resistance. The main heater can be tested the same way and should have a resistance reading of less than 35 ohms.
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Here is an excellent tutorial on defrost systems.

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