Wiring A Defrost Timer

[Janie Mccorey]

HiChuck, I am in the process of restoring a similar 1966 GE ref with the same evaporator system and hot gas defrost. I in fact just used my last timer like I gave you guys for this project [ I bought these from Larry @ Modern Parts in Ohio back in 1999 ]

If you look closely at your old style defrost control you will see tinny #s next to the four terminals that are the same as on the new timer, the timer I supplied is the correct replacement defrost control for your refrigerator, Good Luck Hope this finally gets your ref working properly, John.

Sometimes after working on ADC, mainboards, jazz boards, genesis boards, utah boards, and beta boards, it's a relief to repair a fridge where the defrost is controlled by a good old standard timer. That is until you have to use the Whirlpool universal timer and have to re-read those "encoded" instructions. Over a year ago, when I had some time (and this timer) on my hands, I decided to break that code. Recently, I discussed this info but forgot what I came up with and it took some time to find my post.

When I cannot find the wiring diagram for a Whirlpool manufactured fridge, the following has worked for me when installing the whirlpool universal timer (the one with the innocuous looking dangling black wire)

A)According to the timer manual, For whirlpools If your timer connector has a white wire it is continuous (or possible a cumulative version 2, but hook up is the same) use procedure 1 (black wire to terminal MARKED #1...which does not mean the first pin)

C) Cumulative version 2 uses procedure 3 which is the same as procedure 1(blackwire to terminal MARKED #1)...but usually there is a red and a white wire....but since you already determined there was a white wire you should have used procedure 1 anyway(terminal MARKED #1).

Answer Neil,If the timer wiring harness Has a white wire place the loose black wire on terminal #1 If the timer wiring harness does not have a white wire place the loose black wire on terminal #2

Answer Hello Giwatcher, thank you for contacting APP,From the information I have the loose Black motor terminal lead wire should be on terminal 2, the only real difference should be Cumulative vs Continuous Defrost Timer.

the Whirlpool Defrost Timer Is An Oem Replacement Part for Whirlpool Refrigerators. the Defrost Timer Regulates the Automatic Defrost Cycle, Which Prevents Ice Buildup on the Evaporator Coils in the Freezer Compartment By Sending A Signal to the Defrost Heater to Turn on and Melt Any Ice Buildup on the coils.

One thing to note; the cutoff thermostat may be open circuit until the evaporator tubing is frosted fully, so the timer may not run until the fridge is down to temperature. Some of them are in the 30 degree turn-on and 55 degree turn off range. So if the fridge has not been running, the defrost timer may not run for an hour or more until it cools the evaporator down.

Jake; with all due respect, the timer motor has a complete circuit through the components highlighted below. The power path will change when going from Cooling and Defrost mode as shown by the highlighted path.

With an appliance such as this, there can't be an intentional connection from power "Live", to PE (equipment ground) through a component. Whine it's true that the timer motor does draw only a tiny amount of current, it's just not something which would be done with a 120V plug-connected appliance.

For instance, when in cooling mode, the current for the timer comes from the "Live" side of the power cord, the cold control, through the timer motor, and then back to Neutral through the defrost thermostat and heater. The heater has a very low resistance (maybe a few hundred ohms) and the timer motor has a very high resistance (thousands of ohms). Therefore, the voltage will be divided between the two resistances proportional to the resistances. The timer motor will get almost full voltage, while the heater gets a tiny voltage. For this to work, the heater and defrost thermostat must be good, and closed.

Also, while in Defrost mode; the current for the timer comes from the "Live" side of the power cord, through the cold control, through the timer motor, and then back to Neutral through the compressor motor. The compressor motor winding has a very low resistance (less than 10 ohms) and the timer motor has a very high resistance (thousands of ohms). Therefore, the voltage will be divided between the two resistances proportional to the resistances. The timer motor will get almost full voltage, while the compressor gets a tiny voltage (probably less than one volt).

Can you send a model or part number of the defrost timers used? It may need a nonstandard wiring configuration to function in this circuit. If the timer came with some wiring diagrams, that would be helpful.

I have a Kitchenaid (model ktrp20khbt00) and whenever it goes into defrost mode, it turns the lights (in freezer and refrigerator) off and it doesn't even perform the defrost. I've changed the defrost timer and it is still doing the exact same thing. Now I have ice building up every 2-4 days and no lights. If it's not the timer, what else could it be?

@jayeff I did hire a service tech and he's been here 5x in the last 2 months and still cannot fix it. The last time he was here, he took out the defrost timer and put in some sort of loop to make the light and icemaker work, which obviously causes the ice to build up. I have since put back the defrost timer and we're back to square one. What I can't figure out is where do the two wires in the front go (the brown and pink wires coming from the defrost timer connection)?

Disconnect the power to the refrigerator and then unplug the defrost heater- part #WP2315530 (supplier example only) which is located under the evaporator unit, from the wiring harness and use an Ohmmeter to test it for continuity. I don't know what its resistance value is but it shouldn't test open circuit.

If the heater is OK, here's a video that shows how to test a bi-metal defrost thermostat -part #WP4387503 (supplier example only). The defrost thermostat is also located near to the evaporator unit inside the freezer compartment.

Here's the tech sheet for the refrigerator that has the wiring diagram. Both the full detailed schematic and the simplified version that may also help, especially if it is a wiring problem with the lights.

That end of the brown and pink wires go nowhere. They are test points as shown in the wiring diagram. The other end of the wires go to the defrost timer - bi-metal defrost thermostat connection and the bi-metal defrost thermostat - heater connection - see image below.

The temperature thermostat opens when the correct temperature is reached and this stops the defrost timer motor, compressor motor, evaporator fan motor and condenser fan motor from operating. When the temperature in the compartments warms up, the thermostat closes and reconnects power to the defrost timer motor, compressor motor, evaporator fan motor and condenser fan motor and they start to operate again.

When the defrost timer has operated for a cumulative compressor run time of 8-10 hours the defrost timer contacts switch over and disconnect power to the compressor motor, evaporator fan motor and condenser fan motor and connect power to the defrost heater.

The bi-metal thermostat in the heater path is a safeguard to prevent the evaporator unit from getting too hot and damaging it. It is only thin Aluminium and can be easily damaged by excessive heat from the heater which is directly beneath it. If the temp gets too hot the bi-metal thermostat operates and disconnects the heater. When the temp cools down again it releases and allows the heater circuit to be ready for the next defrost cycle.

The defrost timer motor continues to operate and when the set time for the defrost cycle has elapsed, the contacts switch back and disconnect the power to the defrost heater and connect power again to the compressor motor, evaporator fan motor and condenser fan motor turning them on to get the refrigerator back into normal operation.

@jayeff, so I changed the defrost timer and the bi-metal defrost thermostat and the problem still persist. Actually, when the timer switches to defrost mode it shuts the lights and icemaker down. Therefore, when I manually move it out of defrost mode, the lights and icemaker starts to work again. Could it be that the defrost heater is causing a short and shuts everything else off? The heater element is the only thing I have not yet changed. Let me know if you have any ideas, it's becoming quite a puzzle here and I'm stumped.

Looking at the tech sheet wiring diagram, the timer should have no effect on the lights or the ice maker as they are connected in parallel with the timer so there should always be power connected to them -see the simplified wiring diagram on the right side of the page of the tech sheet at the bottom.

Hi @jayeff, yes, you are correct and I would have tested it but I honestly wouldn't know how to do that or read the schema (or understand it) as I'm just a homeowner and not a technician. It was easier to replace parts as I can get instructions online on how to do those things. Having said that, when you say something is shunting the voltage when in defrost mode, what could be causing that? It's likely be a number of things, but where would you start to look?

To test you would have to be dealing with exposed potentially lethal AC voltage to check what is happening so I would rather not try to explain how to do this mainly for your safety and my peace of mind.

The power should NOT be missing from the ice maker or the lights just because a defrost cycle is happening, so if it is then either there's a wiring problem or if something was shunting the voltage down (and you would have to measure this to know and this is dangerous if you don't know how to test lethal AC voltage safely) then if it were and there was excess current flowing because of this why isn't the house fuse blowing (or breaker tripping) or is it just too low for the lights not to even glow (which is strange) and not blow the fuse.

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