How a washing machine door lock or interlock works

by / Friday, 20 February 2015 / Published in Door Locks & Switches, Washing machines

This video will explain how a washing machine lock or interlock works and how to test them.

How can you tell if a door interlock is faulty?

Washing machine door locks really only get 3 major faults

  1. The points between live and common fail in some way.
  2. The NTC heater or bi-metal strip fail.
  3. The plastic gets to hot and distorts inside the lock causing it to jam.

 

Understanding how a door interlock works helps you decide if it is faulty or not.

Washing machines must have some way in which you can lock the door closing mechanism when the machine is started up and then unlock them with a certain delay (normally two minutes) after the current has switched off via the program or on/off switch, in order to ensure that the door cannot be opened while some of the components are still rotating initially (in particular the motor and the drum of the spin-dryer).
When you shut the door, the latch on the door pushes inside the door lock onto a sliding bar which moves over and activates an electrical part inside which locks the door shut. At the same time, power is passed through the interlock on to the rest of the machine. The actual latching shut of the door is a simple spring-loaded mechanism where the latch just slips into the door catch and the door stays closed. Locking the door is a separate process.
The locking of the door.

locking pin on a washing machine door lock or interlock

locking pin on a washing machine door lock or interlock

Washing machines have a bi-metal strip inside the door lock which is heated by PTC Heater (resister) when live and neutral are activated on to the pcts it heats up and bends the bi-metal strip which then moves the arm to activate the common terminal and push a pin into the closed door to lock it in place. Once this has happened (usually a second or so see video) the power then can flow through to the common wire, and therefore on to the rest of the machine allowing it to start.
The only test you can do without a test rig is to check the PTC Heater on the live and neutral you might expect to get a resistance reading of something like 1000 Ohm but this can vary depending on manufacture of the interlock and the condition of the PTC,

 

burnt part of bi-metal strip

burnt part of bi-metal strip

The parts of a lock

The parts of a lock

the common and live contact

the common and live contact

Faults to look out for

  • It is common for the wires to sometimes be burnt on the terminals due to lose connections and overheat and burn the wiring block. The points that activate the live to common can carbonise and burn. If wires are burned and have gone discoloured or hard they may need stripping back and new connectors will need to be fitted.
  •  PTC Heater can get bad connections and become open circuit.
  •  The door latch may not properly activate the electrical part of the interlock.
  •  The plastic parts inside may have over heated and distorted, stopping the lock from working correctly.
  •  If a metal slide bar is fitted these can corrode and become rusty.

Please note not all interlocks are the same and wiring will differ from manufacture to manufacture.
Do not assume anything about the wire connections on your machine unless you have the wiring diagram. They may be in totally different positions on different machines. Unless the connections are marked Live Neutral and Common you would need to work it all out with a continuity test meter. If you get the wires the wrong way round you can blow the device and possibly blow the PCB or programmer. It may be possible for a fourth wire on some lock to carry power to an LED which may indicate that the door is closed and the interlock activated.

inside of washing machine door lock or interlock (2)




52 Responses to “How a washing machine door lock or interlock works”

  1. Paul says : Reply

    Some washer door locks have a nylon strip that runs from.a lever to the bottom of the machine. If the lever is not pulled down the idea is it is because the drum is low on the suspension and must be too heavy because it is presumably full of water making it heavy.
    However the nylon strip can stretch or the suspension get a bit weak making the door not open.It is a mechanical extra as well as the electrical part of the door locl

  2. Eddy Mupeso says : Reply

    I have a Bosch wfd 1060. The door handle broke .
    What are the connection pins ie live, common and neutral on the interlocking switch

  3. Giang says : Reply

    Thanks very much for explaining, but I have a another door lock switch type DLS-35S-4A (NTCY001EC4) of Toshiba and I could to find the ít’s schematic.

  4. Joe says : Reply

    I have an Aquarius TVM 562G HOPTPOINT DRYER. The door interlock switch is broken and i cant work out how to take the old one off, can anyone please help

  5. Vishwanath says : Reply

    Hi Paul,

    Thank you very much !!
    You have very nicely explained the parts and functioning.

    I was able to solve the problem my self (IFB did not have stock of the spare and instead of waiting, I calibrated/tightened the screw behind bi metal strip so that switch is always in closed position.
    And removed the lock lever so that it will not hinder opening the door.
    DIsadvantage is that door could be opened even while washing in progress. BUT it solved my problem of waiting until stock arrives.

    And further, I can fix the new switch myself.
    (Else, I have an experience of paying heavy charges because an IFB technician came and replaced motor unnecessarily, instead of just cleaning it)

  6. ernest says : Reply

    1 My washing machine is a LG model wm1480FHD where is the live
    2 Where can I purchase a new switch for this machine in the uk
    3 LG cannot help

  7. Charles says : Reply

    I have a Whirlpool top load (Maytag) I use for work clothing and would like to bypass the lid switch. I am an electrician/technician. Model number WTW6200VWO Serial # CY4470791. If I had a schematic I am sure I could figure it out. I didn’t want to take the lock apart because it is good. Thank You

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  9. Deus says : Reply

    I have Samsung machine but the neutral from the board is not reaching the door switch only the live wire reaches the switch. Could there be a problem with the board.

  10. PRAMOD KANAKA says : Reply

    Hi , my washing machine stopped working half the way when the circle was going on and the door starts to make tak tak sound more than the usual no of time when trying to on the circle again. My washing machine model is Hotpoint Aquarius WDL520. Please advise

  11. golden.sakura says : Reply

    i have a 4 terminals door lock switch of LG washing machine front load. How do I identify which one is the common, line and neutral. And also, how can i temporarily bypass the door switch. Thanks..

  12. David says : Reply

    Hi,I hope you can help,we have a Indesit IWB71250 UK ,We need a door lock,ones listed are different the pins are 2,3,4
    ours has pins marked 5,4.3 ,can you help with this,kind regards David

  13. Gizachew says : Reply

    Hi Thanks a lot the explanatory video. it’s very much helpful. I got IGNIS IMAX9s which show E01 either at the beginning of the washing cycle or somewhere in the middle of the washing cycle.
    can you please help?
    what shall I do?
    shall replace the door-lock?

    Thanks in advance.

  14. Rohit Fadnis says : Reply

    Hi Paul, nice description.
    But my problem is somewhat different, I have an IFB front load machine, and door lock was inoperational before, so I bypassed the circuit and was working for almost 1 year.
    Today the connector is completely burnt, it has 5 wires and their is no was to figure out which wire is going where as the connector is burnt and even the wires are melted.
    Could you please help me how to reconfigure the connection, it has 2 black 2 grey and 1 white wire.

    Thanks
    Rohit Fadnis

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