How does my washing machine door interlock switch work? - Page 1
Forum section: electronics / beginners

author: michaelp
author_rank: Contributor
timestamp: June 05, 2014, 12:31:34 pm
content: I bought a front loading washing machine (Samsung, J845) that was missing it's interlock door switch, so I bought a new one. I'm sure I've got it wired correctly, but can only get it to work if I manually engage the switch. Can anyone explain how the switch is supposed to work.I can't for the life of me figure out how it's supposed to complete the circuit with just the door being closed and thus start the rinse cycle.Here's the switch in it's default position. Just as if the door was open, the sliding bar obviously blocks the red pin (see below) from engaging/making contact.Here's the switch when the door is closed. I would expect when I manually slide the bar (as pictured) that the red pin will engage (move towards the camera?) however it doesn't, thus it doesn't "engage" automatically.If I flip the switch over and manually push it down, thus making contact internally, then the washing machine works! But I have to manually hold it from the backside.What am I missing here? What is supposed to make the red pin engage? When the door is closed, is the red pin supposed to move by itself by electric force? or something?Here's a picture of the switch's internals if it's relevant.

author: GeoffS
author_rank: Unknown
timestamp: June 05, 2014, 12:36:42 pm
content: Brand of washing machine?Model number?

author: michaelp
author_rank: Contributor
timestamp: June 05, 2014, 12:38:29 pm
content: The washing machine is a Samsung, model is J845.

author: Paul Price
author_rank: Super Contributor
timestamp: June 05, 2014, 02:03:04 pm
content: The switch is of the bi-metallic type and works as it heats up when the door is closed and the water level or start switch is activated and so the parts inside move to lock the door.So one of the connections goes to mains hot and to one side of the heater wire on the bi-metallic switch. The second wire connects to mains-return to heat the bi-metallic element when the door is closed. The wire wrapped around one of the switch arms heat up and causes it to close the switch mains connection going to the water switch/motor and also locks the door.The third connect is the mains output power and wired to the water level switch and this activates the motor when there is a little water level present in the tub.Once activated by heat, it takes 1 to 2 minutes after the machine is off for the bi-metallic switch arm to cool enough to move into position to release the lock before it will allow the door to be opened.

author: paulhm81
author_rank: Regular Contributor
timestamp: June 05, 2014, 07:26:26 pm
content: the bi-metal in my washing machine gets around 50V and it switches in a few seconds. You should check if it gets around that voltage. The bi-metal acts like a resistor and when it heats up it's size almost doubles and trips the steel blades. You should see resistance on the two pins that should get that ~50V and when it's on you should see a short between two other pins. Those tell the machine it's safe to start the program.

author: michaelp
author_rank: Contributor
timestamp: June 06, 2014, 02:39:42 am
content: Thanks for the replies guys, this is doing my head in! In what I believe to be the right connection, the washing machine works but I manually have to hold pin engaged - the switch mechanism doesn't appear to get warm in this position.If I try some other wiring combinations, the switch engages automatically and it warms up as you both suggest should happen - however the washing machine still thinks the door is unlocked and won't work.The blue/white wires appears to be 240v. And the black wire (which is visibly thinner) doesn't have a voltage across it, so it obviously goes to the water level switch.

author: michaelp
author_rank: Contributor
timestamp: June 06, 2014, 04:34:46 am
content: What would be the reason for the switch to function correctly if manually engaged? Like I said, if I manually hold the red pin engaged, everything works perfectly.

author: IanB
author_rank: Super Contributor
timestamp: June 06, 2014, 07:07:03 am
content: You said the washing machine didn't have a switch installed when you got it. Suppose perhaps that the machine had this problem when the switch was installed before, and the previous owner removed the interlock switch in order to use the washing machine? In other words, there could be another fault in the washing machine somewhere else?

author: michaelp
author_rank: Contributor
timestamp: June 06, 2014, 07:25:41 am
content: Quote from: IanB on June 06, 2014, 07:07:03 amIt doesn't work at-all with the interlock missing. I've got it working correctly now with the interlock installed, but with the red pin held manually engaged like so with a piece of plastic:As-soon as I take the plastic out, the red pins recesses back into the switch because the bi-metal strip hasn't expanded as it's not heating up. This wiring combination is I'm 99% sure correct.There is a different wiring combination I've found that causes the bi-metal strip to heat up and it all appears to work correctly (automatically engages after a few seconds), however whether the pin is in or manually held out, it still registers as the door is open.

author: michaelp
author_rank: Contributor
timestamp: June 06, 2014, 07:32:22 am
content: Quote from: paulhm81 on June 05, 2014, 07:26:26 pmGiven this interlock; are you able to tell me what pin is supposed to be fed what?

author: Paul Price
author_rank: Super Contributor
timestamp: June 06, 2014, 12:07:24 pm
content: Buy or borrow a multimeter, any kind that cam give you any crude idea of a measure of resistance. You should be able to measure a resistance between two of the terminals. One of these two pins you are now connected to is the Hot mains wire, the other returns to the control computer to activate the heater on the door switch.Now. the remaining third connection is the mains output connection to the motor/water level switch.Connect one wire of the meter to third connection and manually press on the switch. You will then notice one of the connections has 0-resistance. This is the AC mains connection to AC Hot.It is possible that the switch was once miswired so that the AC-Hot connected to the control computer board caused the triac that is responsible to heat the bimetallic switch resistance has been burnt out.It is also possible that a small piece of plastic/metal in the door lock mechanism has been damaged/removed to get the washing machine to work without the switch locking the door, before or after an alleged triac burn-out event on the control board.If the switch is wired correctly and heats up it is also a third possibility is that the switch position relative to the locking tab on the washer door needs to be adjusted to allow the lock to close/open properly.I f you can get the washing machine to work in any way, then clothes are washed and there is peace and happiness throughout the homeland. If you fret over safety issues of flashfloods and damaged bodyparts because someone has the decided to open the machine door while it is plenty with water or violent motion, then you have to decide whether you want to throw out the baby with the bathwater(as in buying another washing machine) or deal with a small caveat in machine operation.

author: G7PSK
author_rank: Super Contributor
timestamp: June 06, 2014, 05:43:41 pm
content: Have you checked that power is being fed to the interlock switch, what you are describing ie. the machine works while you hold the interlock closed suggests that no power is getting to the switch, without power on the switch the contacts will not close so the machine wont run.

author: michaelp
author_rank: Contributor
timestamp: June 06, 2014, 11:18:22 pm
content: Thanks Paul Price and G7PSK.I've got a busy weekend, but I will be checking this all out Sunday night/Monday morning and will check back with results. I noticed last night that when the machine is turned off (via the front panel), it's making a very slight humming/buzzing noise. So I'll be turning it off at the power point while not in use until I check it over a little more.

author: cdacunha71
author_rank: Newbie
timestamp: June 07, 2014, 08:50:08 am
content: I think it's probably the most obvious solution, a mechanical problem. Someone has removed the pin or whatever from the door that pushes the switch when the door is closed

author: paulhm81
author_rank: Regular Contributor
timestamp: June 07, 2014, 07:34:55 pm
content: there is no water level on this lock. There is only the voltage for the bi-metal and a feedback so the machine knows that the door is locked before starting the program. If you have e meter, the high voltage should go on the pins where you measure a resistance and the other one should return somewhere to the main board.You said - "If I try some other wiring combinations, the switch engages automatically and it warms up as you both suggest should happen - however the washing machine still thinks the door is unlocked and won't work."When you got it to warm up, did the lock work ? I'm not interested if the machine new it was locked but if it was mechanicly working. In my lock the third pin with the common pin tell the mainboard that the door is locked.