Testing A Washing Machine Pressure Switch

Are you having the unfortunate experience of loading up your washing machine and pressing the start button only to have the washer start to overflow during the fill cycle? Perhaps the washer seems to be functioning normally, but unexpectedly stops working just before the rinse cycle? Or, maybe, the appliance isn’t starting at all? All three of these problems can be caused by the same thing: a malfunctioning pressure switch.

Repair Clinic has a solution for identifying a broken pressure switch so you can get your washing machine working efficiently again. Let’s start with how a properly operating pressure switch is used throughout washer operation:

How a washing machine pressure switch works

Simply put, a washing machine pressure switch is a mechanical component that controls how much water will enter the tub for a wash cycle on numerous washer models.

The pressure switch will shut off voltage to the water inlet valve

Once the washer control or timer is set to the selected wash cycle and the start button is pressed, the control will send voltage to the appliance’s water inlet valve which opens and allows water to fill the tub. The pressure switch has a tube that connects to the side or bottom of the tub. As the tub fills with water, air pressure increases in the tube. When a sufficient amount of water has filled the tub (8 to 18 gallons in a typical top-load washer; 2 to 5 gallons in a typical front-load washer), the pressure in the tube causes the pressure switch to shut off the voltage to the inlet valve, closing it and stopping the water flow. The voltage is then directed to the washer’s drive motor or a rotor/stator assembly to start the wash and agitation cycle.

The pressure switch is used during the rinse cycle as well

Following the wash and agitation cycle, the water in the tub will be drained and fresh water will enter the tub for a rinse cycle. The pressure switch will again allow voltage to be sent to the water inlet valve once the water has drained from the tub to allow the appropriate amount of fresh water in. When a sufficient amount of water has entered, the pressure in the air tube will signal the pressure switch to shut off the voltage to the inlet valve once again and allow that voltage to be directed to the drive motor or rotor/stator assembly to initiate the rinse and spin cycles.

How a washing machine pressure switch can malfunction

The fill and rinse cycles are dependent on the pressure switch and the attached air pressure tube operating properly. If the switch has shorted closed or the air pressure tube has a hole in it, too much water may be allowed to enter the tub, causing it to overflow.

If the air pressure tube has a blockage or the pressure switch is defective and has no electrical continuity, the washer may not fill or start at all. An intermittently failing switch unable to detect that water has drained from the tub could result in the washing machine stopping mid-cycle.

How to test a washer pressure switch

To determine if a faulty pressure switch is the cause of your washer problem, there are four steps you can take to inspect and test the component:

  1. Remove the pressure switch and air pressure tube from the washer – For proper test results, the pressure switch and the attached air pressure tube will need to be uninstalled from the washing machine. Before you begin any disassembly, be sure to unplug the appliance’s power cord or shut off the power to the unit. On front-load washers the pressure switch is usually located directly under the top panel, often attached to the frame. On top-load washers, the switch may be attached to the interior of the washer’s rear panel under the main top or behind the control panel. You will need to disconnect the wires from the switch’s terminals and detach the switch from the panel or frame to uninstall it. Most pressure switches can simply be rotated to free the part. The air pressure tube will need to be detached from an air chamber port on the side or bottom of the outer tub in order to remove the entire pressure switch and tube assembly.
  2. Examine the air pressure tube – Before you test the pressure switch itself, you should examine the air pressure tube. Does the tube have any obstructions? Does it have any cracks or holes in it? If so, that is likely the cause of the problem. You can often just replace the old tube with a new one to resolve the issue. Whether the old tube is in good condition or you’re installing a new tube, just be sure the component fits snugly on the pressure switch port.
  3. Identify the pressure switch’s terminals – Washer pressure switches will typically have three terminals: a common terminal, a normally-closed terminal, and a normally-open terminal. The normally-closed terminal provides power to the water inlet valve while the normally-open terminal provides power to the drive motor or the rotor/stator assembly. You will need to refer to the washing machine’s wiring diagram to identify each terminal for the purposes of testing the component.
  4. Use a multimeter to test the pressure switch terminals – You can use a standard multimeter or ohm meter to test the pressure switch for appropriate changes in electrical continuity. Start by rotating the range selection dial to the lowest setting for ohms of resistance. Contact the black meter lead to the pressure switch’s common terminal and the red meter lead to the normally-closed terminal. The multimeter display should indicate close to “0” ohms of resistance, meaning the switch has continuity.

Keeping the leads on the same terminals, put the end of the air pressure tube against your lips and blow into it. You should hear a clicking sound and the meter display should indicate the common and normally-closed terminals no longer have electrical continuity.

Next, move the red lead to the normally-open terminal while keeping the black lead on the common terminal. The meter display should indicate no continuity until you blow into the air pressure tube which should cause electrical continuity to be established between the common and normally-open terminals. If the pressure switch terminals test negative for continuity throughout the test or positive when they should not, you’ll know the pressure switch is defective and will need to be replaced.

Repair resources from your repair partner

As your repair partner, Repair Clinic has the resources you need to successfully fix your washing machine. Just enter the appliance’s full model number in the Repair Clinic website’s “Videos & Articles” search bar to find model-specific guides, schematics, and step-by-step procedural videos, such as this one showing how to replace a pressure switch on an Electrolux Front-Load Washer (Model EFLS627UTT) or this one showing how to replace the air pressure tube on a Whirlpool Top-Load Washer (Model WTW4815EW0).

Use genuine not generic parts to fix your washing machine

If you need to install a new pressure switch, air pressure tube, or any other washer component, it’s best to purchase a genuine manufacturer replacement part instead of a generic non-OEM part. While genuine parts are specifically designed to work with the model they’re built for, generic parts may not be completely compatible with the appliance or could be made from inferior materials that can wear out quicker. Repair Clinic is the place to find original manufacturer replacement parts that match the most popular top-load and front-load washer models, including those built by Whirlpool, LG, Samsung, Maytag, GE, Kenmore, Bosch, and Frigidaire. Entering the full model number of the appliance in Repair Clinic’s “Search Parts Online & Get Answers” search bar will result in a comprehensive list of compatible OEM parts related to that model. You can then use the “Part Category” and “Part Title” filters to narrow that list down to find the exact part you need to repair your washer.

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