Defrost Timer Wiring Diagram

[Silvina Spindler]

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.

I've been having defrost issues with my Whirlpool refrigerator, and I am at my wits end! What is happening is that it does not enter the defrost cycle on its own; rather, I have to manually turn the timer with a screwdriver to get it to defrost. I have replaced the following items: Defrost timer (twice), defrost thermostat and regular thermostat for refrigerated section. Once I manually initiate a defrost, the heater does come on and melt and ice in the freezer, and after about 20 minutes the timer switches back to cooling cycle, but does not automatically go back into defrost roughly 8 hours later (its rated time). This refrigerator does not seem to have any sort of defrost control board, as I looked over the parts diagram for this unit. I really don't know what else could be causing this issue. All replaced parts were OEM and correct to this Whirlpool refrigerator, and I did test them via recommendations elsewhere online. Please, if anyone has anything that could help me try and solve this I would greatly appreciate it. Thanks so much!

If you received on with the flying lead, (a lead for the motor that has to be pushed onto one of the terminals), and you didn't read the instructions correctly and install onto the correct terminal, the motor will not advance correctly.

The only other thing I can think of at this point is that there is a wiring issue somewhere within the refrigerator, but if the defrost timer advances on its own once I manually put it into defrost, it should be getting power to the timer. I don't want to keep throwing money and time into this, but trying to avoid getting a new refrigerator if I can fix this.

Update: After some more testing, I found something interesting. When running normally out of defrost cycle, Pin 2 ALWAYS has 120V across it, which is ONLY supposed to have a drop across it in the defrost cycle. Pin 1, on the other hand, does NOT have 120V across it outside of the defrost cycle, and should until it enters the defrost cycle. There is some sort of mix-up somewhere in the wiring, so could it be the wiring harness in the freezer itself? I need to find a schematic for this refrigerator, but this whole issue is just so bizarre and confusing...

Also, in this setup, after the the defrost t-stat opens and the defrost timer comes out of defrost the timer doesn't start advancing again until the evaporator gets cold enough to close the defrost t-stat.

Ok, so I did some more testing last night and checked the timer this morning. I made a mark on the defrost timer last night to see if it had advanced, and after checking this morning it had moved quite a bit. I took some measurements in voltage at pins on the timer, and came up with test values (all referenced to ground):

All are as to be expected. However, I checked the timer for advancement a few moments ago, and it has not seemed to have moved since checking it this morning. I checked the above pins again, and came up with the same results. So, the timer only advances when the defrost thermostat is closed from my understanding. However, when I check for a drop across pins 2 and 3, I get a value of 120V, which would indicate that the defrost thermostat is closed, correct? If so, then is there any reason why the defrost timer has stopped advancing? The compressor has been running, so it should definitely be moving.

None i can think of, If you have 120 vac At pin 2 (pink) to pin 3 (red) the timer motor should be running. The cam movement is very slow, does this timer have a window to see if motor is running? Keep and eye on it and hopefully it will go into defrost by itself. Once a day should be more than enough to keep evap clear.

No, unfortunately no window on this timer. I did, however, make a mark on the timer and the small dial to see if there has been any movement. It's just so strange that it partially works, then stops. I even went so far as to set up a test rig with just the timer itself removed from the refrigerator and applied 120V to both pins 1 and 3 to see if it moves, which it does. At this point, I really don't know what else to try. Wouldn't seem like a wiring issue if I'm still getting the correct readings from all of the pins on the defrost timer. This is very frustrating, considering there is not much to this refrigerator in general.

Oh, and to add to the above, I even tried another known good compatible defrost timer to rule out any issues with the other one. Same result as the other one, where it just does not advance the timer.

That's the only other thing I was thinking. I checked last night when I was checking the defrost thermostat, and didn't see anything unusual with the wiring in there. If it's in the main harness that runs through the refrigerator through to the freezer section, that would be bad as I don't even know how I'd end up replacing that if there were a problem there.

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.

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