Before we expose the evaporator to diagnose a defrost problem, you need to have an idea of what you will be seeing when we open it up...the defrost system and its parts. There are components that need to be as cold as possible before testing them. If you expose the evaporator, and then spend an hour reading about the defrost system, precious time and ice are melting away....
When the compressor is in operation, the evaporator is VERY cold...on the order of 10° to 15° F below zero. The air inside the refrigerator is very cold and dry. All the cold air is made in one place, and then distributed throughout the freezer and fridge compartments, usually by fans. So airflow inside the refrigerator is important.
The ambient air in your kitchen is much warmer and more humid...even if you live in a dry climate. When you open the fridge or freezer door, the warm moist air gets inside.
When the moist air hits the evaporator, the water freezes instantly, causing frost to form on it. If enough frost forms, it can block the airflow inside the refrigerator.
If cold air is not flowing through the refrigerator, then the spaces inside it...the fridge and freezer...will start to feel warmer than normal. However, the evaporator panel will still feel frozen...that is where the cold air is made.
That is what causes the strange symptom of ice buildup in the freezer, but melting ice cream and meat. Seems kind of counter-intuitive.
So what do we do about frost?
Well, heat melts ice. So below your evaporator is a defrost heater. And every few hours, a defrost timer turns off the compressor, and turns on the defrost heater, to melt the frost.
The timer determines how long the heater stays on, usually 20 minutes or so. After that, the timer stops the defrost cycle and turns the compressor back on, starting another cooling cycle.
Defrost heaters run VERY hot...some of them even glow red.
Let's say the timer is set to defrost for 20 minutes. What happens if the frost melts in just 10 minutes? If the heater stays on, it can actually start to heat up the freezer compartment, or burn nearby wires. So to turn off the defrost heater before the timer stops it, a defrost thermostat is installed above the evaporator. If the frost melts quickly and the temperature starts to rise, then warm air will rise and hit the defrost thermostat. The thermostat opens, and stops the heater. The refrigerator will just sit there doing nothing, neither heating nor cooling, until the defrost timer starts the cooling cycle again.
One more thing...the heater turns the frost back into water. What happens to the water?
Beneath the heater and evaporator is a defrost drain pan. The pan collects the water and drains it outside of the refrigerator, to a another pan on, or somewhere near the compressor. Heat from the compressor evaporates the water back into the ambient air.
So to recap, the major components of the defrost system are the defrost timer, the defrost heater, the terminating thermostat, and the defrost drain pan.
Whirlpool made a special machine in the 70's, and a LOT of them are still in service.
The icemaker head IS the defrost timer!
The troubleshooting procedures are different for these machines than for others.
So we need to know if you have one of these machines before we proceed with our diagnosis.
You can recognize this type of machine by the shape of the cube it puts out (or would put out, if it was working).
The hard-tray Whirlpool/ Kenmore produces "half-moon" shaped cubes.
It is finished in a dark gray or black color and has rotating fingers that eject the cubes from the unit.
The flex-tray produces "rounded rectangular" cubes.
It has a white plastic, flexible tray that inverts and twists to eject,
much the same as a manual ice cube tray would work.
Note that there was a replacement timer made,
with just the timer and not the actual icemaker tray.
If you have what looks like an icemaker head in your freezer,
but there is no icemaker behind it, then you have a Flex-Tray refrigerator.
The hard-tray and separate defrost timer is by far the more common arrangement.
In most older refrigerators and some newer ones, a motor-driven timer is used to stop the compressor and turn on the defrost heater. This timer controls how often the cycle occurs, and how long the compressor stays on. With a timer, this is a fixed cycle; for example, the refrigerator might be in the cooling cycle for 10 hours, then spend 20 minutes in the defrost cycle.
If your refrigerator is operating in the tropics, in really warm, humid air, it will need to run a lot and defrost often. And if the door is opening and closing a lot, letting in even MORE warm humid air, it will need to cycle even more often.
In a cold climate, it probably will not need to run nearly as long, or defrost nearly as often.
Compressors and defrost heaters use a lot of energy, so to make refrigerators more efficient, refrigerator designers are minimizing the total amount of time that they stay energized.
To adapt to these different conditions, designers are using electronics...solid state circuit boards with microprocessor logic. Such techniques are called Adaptive Defrost Control, commonly abbreviated as ADC.
To make decisions about how long and often the refrigerator cools and defrosts, the control board must have input about the conditions that the fridge is operating under. Each manufacturer uses a different logic scheme and different inputs, not just temperatures, but things like how long the refrigerator door stays open, how long the compressor runs, and the duration of the previous defrost cycle.
For example, door open info is provided to the logic board by the door switch - the same one that controls the refrigerator's internal lights. If the light bulb is burnt out, the ADC will still accumulate door open time. However, if the door switch has failed, the next defrost will occur either too quickly or too slowly.
Some designs even have a "vacation mode;" for example, if the door has not been opened in 72 hours, the refrigerator will not defrost as often.
How often defrost occurs may also be shortened under certain circumstances. For example, the ADC is programmed with a maximum amount of time that the heater can stay on; say, for 16 minutes. If the heater stays on for the maximum amount of time, without being stopped by the terminating thermostat, the microprocessor will assume that not all of the frost melted, and it will initiate the next defrost cycle much sooner.
How can you tell whether you have an ADC or a defrost timer without searching for it on your refrigerator?
The easiest way that I've found is to go to a website such as PartSelect.com. Type in your refrigerator's model number and search for the words "board" and "timer." They have an exploded parts diagram for most model numbers; this can tell you where to search for the board or timer.
Where to find your refrigerator's model number
Some ADC and other control boards in the refrigerator control other functions, too, such as icemaking and electrical air damper door opening and closing. The easiest way to tell the difference between the ADC and other boards is that the harness connection is always labeled with the compressor, defrost heater, L1 and L2. Often the leads are labeled for the defrost thermostat, too, and a sometimes even test connections.
DEFROST TIMER AND ADC BOARD LOCATIONS
Mechanical defrost timers can be a bit difficult to find. They come in many different styles. Often they are mounted under a cover plate or in a bracket that hides all but the advancement pinion. The pictures above show some different styles of timers and what the timer might look like installed, and also some typical mounting locations.
ADC boards are mounted in similar locations to defrost timers. You don't really need to find yours just yet; you only need to be able to initiate a defrost cycle for diagnosing. If, after diagnosis, you need to replace it, then you will need to find it.
Do you have a top-freezer, side-by-side, or bottom-freezer refrigerator?
Remove everything from the freezer, including any shelves.
On the back or bottom of the freezer compartment, there will be a removable panel with a bunch of screws holding it in. We need to know if you have a back-panel freezer, or a bottom-panel freezer.
Remember which one you have. You will be using this info for later diagnosis.
Remove everything from your freezer, including all food and any icemaker and shelves.
Look at and feel the panel covering the back of the freezer compartment. Is it thick with frost?
Are there air vents in the top of the food compartment that are choked with ice?
If the answer is yes to either of these questions, there's probably a defrost problem.
If you suspect a defrost problem, first remove any icemaker that may be installed. You will see a removable panel covering the entire back of your freezer compartment. There may be 6 to 10 or more screws holding it on. In some units there is a light socket attached to the panel.
These can sometimes be quite difficult to disassemble. Make sure the power is off the refrigerator before disassembling any lighting circuit.
The panel may be frozen to the evaporator beneath it; be careful you do not bend or break it. Sometimes it pays to take a few extra minutes and melt the ice a little bit first. This can usually be accomplished by blowing warm air on it with a blow-dryer. Do not melt all the ice just yet; only enough to get the panel off. You want most of it to remain there at this point so you can further diagnose the problem.
NOTE: There is something behind the panel called a "terminating thermostat." You don't want to heat it up until after you make your diagnosis. Therefore, it's a good idea to try to avoid melting any more ice than you have to... just enough to get the panel off. If the thermostat opens before you've had a chance to see if the heater works, you'll have to by-pass it. On some models, this involves cutting, stripping and splicing wires. No big deal, but
it's an extra step that's unnecessary if you're careful about melting ice in the first place.
There may be some styrofoam insulation panels. If so, they may be waterlogged and may break when you remove them. It's okay, just keep them in one piece as much as possible and replace them as best you can when you're re-assembling.
You will see a removable panel covering the entire back of your freezer compartment. Is it thick with frost? There may be 6 to 10 or more screws holding it on. In most units there is a light socket attached to the panel. We need to remove this panel.
NOTE: There is something behind the panel called a "terminating thermostat." You don't want to heat it up until after you make your diagnosis. Therefore, it's a good idea to try to avoid melting any more ice than you have to... just enough to get the panel off. If the thermostat opens before you've had a chance to see if the heater works, you'll have to by-pass it. On some models, this involves cutting, stripping and splicing wires. No big deal, but it's an extra step that's unnecessary if you're careful about melting ice in the first place.
Look at and feel the panel covering the bottom of the freezer compartment. Is it thick with frost?
Can you see airflow holes that are choked with ice?
Is there ice forming on, or lots of water on the ceiling of the food compartment?
If the answer is yes to any of these questions, there's probably a defrost problem.
You will see a removable panel covering the entire bottom of your freezer compartment. There may be 6 to 10 or more screws holding it on.
On some models, you may have to remove some of the plastic moulding around the door frame to access some of the evaporator panel screws. Be extra careful; the plastic moulding can be brittle and break easily. The plastic will bend; just go slow. You may even try heating it a little with a blow dryer, to soften it.
The panel may be frozen to the evaporator; be careful you do not bend or break it. Sometimes it pays to take a few extra minutes and melt the ice a little bit first. This can usually be accomplished by placing a pan of very hot water in various places on the panel, or by blowing warm air on it with a blow-dryer. Do not melt all the ice just yet; only enough to get the panel off. You want most of it to remain there at this point so you can further diagnose the problem.
The frost pattern on the evaporator at this point will tell you what is wrong with your refrigerator.
Is the evaporator pretty evenly frosted all over, with white, snowy ice, or clear, solid ice?
Is it frosted just on one or two coils, and then clear on the rest of the evaporator?
A defrost thermostat will be located somewhere in the evaporator compartment, usually to the evaporator itself (by a spring clip) or against the side or back wall of the compartment.
It looks like a small cylindrical disc about 1" or so in diameter and about 3/4" to 1" thick.
It is wired in series with the defrost heater; when it opens, the heater shuts off. One of the two heater wires will lead directly to it.
Defrost heaters are always located in the evaporator compartment. Pictured below are some different arrangements and types. There are three different types most commonly used: glass tube, aluminum tube, and bare element.
Glass Tube Defrost Heater
Glass Tube Defrost Heater Mounting Location (Typical Side-By-Side)
The heating element is encased in a glass tube mounted beneath the evaporator. Sometimes two or three small glass-tube-type heaters will be used instead of one big one; usually you'll see this arrangement in
Glass Tube Defrost Heater Mounting Locations (Typical Top-Freezer)
Aluminum tube heaters These heaters look just like the evaporator tubes and press into the evaporator fins. They are usually used on bottom-evap models. The easiest way to see the heater is to look for the heavy,
rubber-coated wires leading to it; one on each end. Often there are clips holding the ends on to the evaporator coils; watch for these when you remove the heater.
Typical Aluminum-Tube Defrost Heater Mounting Locations
Bare element heaters Found most commonly on top-freezer back-evap models. The element has no protective tubing and generally wraps around beneath the evaporator in a large "U" shape.
You must exercise caution when handling these heaters to prevent burning yourself. They all run very hot; glass tube and bare element heaters even glow red while in operation.
Typical Bare-Element Defrost Heater
Put a broad-tipped screwdriver in the advancement pinion and advance it (clockwise only, or you will break it). Sometimes it takes a pretty firm twist to advance it. You
will feel it clicking. At some spot in the cycle, you will hear and feel a loud click; after you advance it 10-20 more degrees or so, you will feel and hear another loud click.
Between the two loud clicks is the defrost part of the cycle. The rest of the timer's rotation is the "run" cycle. If your compressor is running when you advance the defrost timer, it will stop running when you hit the defrost portion
of the cycle.
Advance the timer all the way around to the beginning of the defrost cycle again (generally one-half or one full turn) and leave it as early in the defrost cycle as possible.
We are about to diagnose the defrost problem, so now is the time to initiate a defrost cycle.
Whirlpool, Kenmore, Thermador, Amana, Roper, and some Maytags and some Jenn-Airs (see
General Electric, Hotpoint, Haier, Cafe, Profile, and Monogram, Fisher & Paykel, and RCA including PROFILE, ETERNA and SELECT models
Frigidaire, Gibson, Tappan, Kelvinator, and White-Westinghouse
Admiral, Magic Chef, some Maytags and some Jenn-Airs
Sub-Zero, Wolf, Cove
Remove the icemaker from the freezer.
Remove the ice tray from the icemaker. It is spring loaded, and simply pushes away from the icemaker head and pops out. Pull or pry the plastic cover off the icemaker head.
You will need to remove the leaf switch to get the drive cam off. Remove the drive cam, the large drive gear and the smaller timing gear.
Temporarily remount the leaf switch to keep it from drifting around and touching things.
The defrost switch is the small, rectangular switch in the upper righthand corner of the icemaker head. Remove this switch from its mounts, but do not disconnect the wires to it. Using electrical tape, tape it out of the way so it does not touch any other metal object in the icemaker head.
Inside your fridge, turn the cold control to a midrange setting.
Plug in the icemaker again. Do not touch any metal contact with your hands; you may shock yourself.
Look and listen to the evaporator. Within ten minutes (usually much less) you should be able to see a red glow from the defrost heater(s), which is mounted beneath the evaporator. You will probably also hear popping and sizzling; this is defrost water hitting the heater and boiling off.
If your defrost heater heats up, then you need to replace the drive gear set in your icemaker. Click below for instructions.
If you see and hear NO signs of the defrost heater heating up, we need to test the defrost switch.
First remove your icemaker from the freezer again.
Remove the BLACK lead from the defrost switch, and electrically test the switch for opening and closing. If you don’t have an ohmmeter, or if you don’t know how to use one, click the button below.
Using your ohmmeter, you should see no resistance between the empty terminal (where the BLACK lead was) and the PINK terminal.
You should also see infinite resistance between the empty (BLACK) and ORANGE terminal.
When you press the switch button, resistance will be just the opposite:
BLACK-ORANGE should show NO RESISTANCE,
BLACK-PINK should show INFINITE RESISTANCE.
If the switch is not acting as it should, replace it.
If the switch is okay, the problem is probably your defrost heater or terminating thermostat.
I just replaced the defrost switch
There are two sets of gears in this icemaker, the defrost gears on the back of the icemaker head, and the drive gears on the front of the head.
Do not remove the motor or defrost gears, or you will have to realign the defrost gears, which can be difficult. If you do, instructions should come with the gear set.
Get a set of drive gears from your appliance parts dealer. When you replace the gear set, it is also a good idea to replace the defrost switch while you're in there.
For a bit more money, you can just replace the whole icemaker.
Align the hole in the small drive gear with the alignment hole in the icemaker head and install the gear. Check alignment by inserting a 3/32" rod into the holes. (a drill bit will do) If they do not line up perfectly, momentarily plug the icemaker in or apply 110 volt power to the two center leads of the plug This will turn the drive motor slightly. Repeat the process until the holes align.
Carefully holding the drive gear in its aligned position, install the drive cam. Line the drive pin up on its hole on the drive gear. Lift the spring-loaded shut-off arm (ice level sensor) as you install the cam and let it rest in the cam hollow. Be sure that the ice level sensor arm loading spring is in the right place. Install the leaf switch. Sometimes the stuff in this paragraph takes three hands and your belly, but be persistent. You'll get it together eventually.
Make sure the wiring for the leaf switch and the defrost switch is routed over the post above the drive gear. Carefully install the metal cover plate, making sure the end of the wire shut-off arm (ice level sensor) is in its pivot hole in the metal cover plate. Install your three screws. The drive pin will pop up through the metal cover plate.
Install the ice tray into the ice maker, and re-assemble your fridge.
The icemaker is now aligned at the beginning of a harvest cycle. When you re-install it, the ice tray will slowly turn one full turn. If the icemaker is being used, the tray will then fill with water. Make sure the icemaker is turned on (ice level sensor arm is down) or it won't make ice.
Now we need to figure out which defrost component isn't working, and replace it.
Look and listen to the evaporator. Within ten minutes or so (usually much less) you should be able to see a red glow from the defrost heater(s), which is (are) mounted beneath the evaporator. You will probably also hear popping and sizzling; this is defrost water hitting the heater and boiling off.
If the heater DOES NOT heat up, we need to test it and the terminating thermostat.
If the heater DOES heat up, the heater and terminating thermostat are working. The problem is the defrost timer; it is not initiating defrost. You need to melt all the ice and replace the defrost timer.
DO NOT touch the evaporator yet. It may have an aluminum tube heater. It will not glow red, but it is hot enough to burn you. Read on.
We want to determine if your defrost heater is working. Try to find your defrost heater and terminating thermostat. You may not see them at first, they might be covered in ice. Give the defrost heater a little time to thaw the ice.
Your refrigerator has one of two different problems.
IF THE ICE LOOKS SNOWY AND WHITE, you have a regular defrost system problem, involving the defrost timer, defrost heater or terminating thermostat. The ice will look snowy and white.
IF THE ICE LOOKS SOLID AND CLEAR (or slightly milky white-ish) then the defrost drain is clogged. In this case the defrost system is probably working correctly and melting the frost. But the defrost water is not draining away from the evaporator. Instead, it is pooling up beneath the evaporator, and when the defrost cycle ends, it re-freezes. When the next defrost cycle happens, the water still can't drain away, and so it just builds up some more. If this happens enough times, the evaporator will just be frozen into one solid block of ice. (It might have a little white-ish coloration, but it will definitely look solid and much clearer than frost.) Usually there will be other symptoms, too, like water dripping from the roof or floor of the fridge, or running out onto the floor in front of the refrigerator.
You initiated (forced) defrost in the last step; the refrigerator should be in defrost mode. Look and listen to the evaporator. Within ten minutes (usually much less) you should see signs that the defrost heater is working. If you have a bare-element or glass tube heater, you may see it glowing red, beneath the evaporator. If you have an aluminum-tube heater, you may see frost melting around it. DON'T TOUCH IT DIRECTLY! IT IS HOT ENOUGH TO BURN YOU! You will probably also hear popping and sizzling; this is defrost water hitting the heater and boiling off.
IF the heater is working, and the ice is clear
the problem is likely that your defrost drain is clogged.
IF the heater IS working, and the ice is white and snowy-looking
the problem is likely that your defrost timer is bad. We will need to replace it, but first we need to melt all the frost that has formed.
IF the heater is NOT working, and the ice is white and snowy-looking
the problem is likely your defrost heater or terminating thermostat.
Now we need to thoroughly melt all the ice in the evaporator compartment.
REMEMBER, THE ALUMINUM FINS ARE SHARP, AND WILL CUT YOUR FINGERS!
If you have a glass tube-type defrost heater, be PARTICULARLY careful not to cut your hands on any broken glass.
NEVER EVER chip or dig out ice from around the evaporator with a sharp instrument or knife. You WILL PROBABLY puncture the evaporator, and if that happens, all the Freon will rush out, and you WILL end up having to buy a new refrigerator.
Use hot water and/or a blow dryer to melt ice, or a heat gun if you have one. You might have to clean up some water, but it's cheaper and easier than buying a new refrigerator. If you use a blow dryer or heat gun, take care not to get water in it and shock yourself.
Better yet, if you have the time and patience, leave the fridge open for a few hours and let the ice melt naturally. You can remove large, loose chunks of ice in the evaporator compartment by hand, but make sure there aren't any electrical wires frozen into the chunks of ice before you start pulling on them.
Always re-install any removed duck seal, heat shields, styrofoam insulation, or panels that you remove to access anything. They're there for a reason.
UNPLUG YOUR REFRIGERATOR. Now find the power leads for your defrost heater, and test the resistance of the heater(s) with an ohmmeter.
If you don’t have an ohmmeter, or if you don’t know how to use one, click the button below.
If the heater or thermostat leads are not connected with spade terminals, you will need to cut the wires to test them.
If the heater shows little resistance (between about about 10 and 200 ohms,) it is working fine. The problem is your terminating thermostat.
If the heater shows infinite resistance, it is bad. You will need to replace it. If you have multiple heaters, you will need to replace them as a set.
Sometimes side-by-sides will have more than one heater. You can test them separately, or as a set, whichever is easier.
Look for any clips or screws holding the heater to the evaporator and/or thermostat. Take note of how they come off. Take pictures if you must...you will need to put them back on. The evaporator fins are sharp and can cut your hands; use gloves.
Be extra-careful replacing glass-tube heaters; if the glass is cracked or broken, you can cut yourself on it.
Remove and replace the heater. It is a good idea to replace the defrost thermostat along with the heater(s). They are cheap.
In replacing heaters and/or terminating thermostats, you can install them using butt connectors, wirenuts, and electrical tape, or spade connectors if fitted.
If you don't know how to use butt connectors or wire nuts, CLICK HERE.
OK, I've replaced my defrost heater and/or thermostat. What's Next?
If the timer is connected by a terminal block, just pull the block off the old timer.
If you have separate wires to the timer terminals, carefully record which wire came off which terminal, by color or by terminal number, or both. Take or draw a picture, if you can. Make sure that the new timer is wired correctly; there should be instructions with the new timer.
CAUTION: If you have a Whirlpool or Kenmore timer with a separate wire coming from the timer motor, it is important to get that wire connected to the proper terminal. If the wire is visible on the old timer, connect it to the same terminal. If you cannot tell for sure, get the information for your model fridge from your parts supplier. If the timer is wired incorrectly, the fridge will frost up again.
Whirlpool / Kenmore Defrost Timer Motor Wire
OK, I've replaced my defrost timer. What's Next?
Finding the the Adaptive Defrost Control board can be difficult. Most of the time they are inside the fridge section, up near the roof, but there are many exceptions.
The easiest way that I've found is to go to a website such as PartSelect.com. Type in your refrigerator's model number and search for "board." They have an exploded parts diagram for most model numbers; this can sometimes give you an idea of where to search.
If you search online, you can sometimes find videos for your specific make, or even model.
If you just can't find it, CLICK HERE to get help from a REAL LIVE HUMAN appliance repair technician. It only costs a few dollars.
OK, I've replaced my ADC board. What's Next?
Get One-On-One Repair Help from a Real, Live Human Being.