Dishwasher Pressure Switch Testing

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Have you found your dishwasher doesn’t seem to be filling with water properly? Or maybe it’s filling too much and begins to overflow onto the kitchen floor during a wash cycle?! Both problems could be caused by a component found on select dishwashers: the pressure switch. In this article, Repair Clinic examines how a dishwasher pressure switch helps to control the water flow as well as gives you a step-by-step method for testing the switch.

How a dishwasher pressure switch controls water flow

Not all dishwashers have a pressure switch, but the ones that do, such as the Danby Model DDW1899BLS1 Dishwasher, will use the switch to control the water flow.

The pressure switch has an attached tube that connects to the dishwasher’s sump

A dishwasher pressure switch monitors the amount of water that enters the tank during the fill cycle. The switch has an attached tube that connects to the dishwasher’s sump, the assembly installed in the middle of the tank base which normally contains a circulation pump to circulate the water during the wash cycle and a drain pump to force the water out of the tank during the drain cycle.

The pressure in the tube causes the switch to shut off voltage to the water inlet valve

As the sump area fills with water during the fill cycle, air pressure increases in the tube. When a sufficient amount of water has filled the tank, the pressure in the tube causes the pressure switch to shut off voltage to the water inlet valve, closing it and stopping the water flow.

A defective pressure switch can cause a major dishwasher malfunction

A defective pressure switch can cause a major dishwasher malfunction. If the switch falsely determines that the pressure in the air tube is higher than it actually is, the pressure switch will shut off the inlet valve prematurely, preventing the tank from being filled with enough water for an effective wash cycle. Or, if the faulty switch is unable to detect increasing pressure in the tube, it can allow the inlet valve to stay open too long, resulting in too much water entering the tank and causing the dishwasher to overflow.

How to test a dishwasher pressure switch

To help determine if the dishwasher pressure switch is defective, you will need a multimeter to test the switch for appropriate changes in electrical continuity – a continuous electrical path present in the part.

You will likely need to uninstall the dishwasher to access the pressure switch

The pressure switch is usually attached to the dishwasher’s lower left or right frame, or directly under the sump. You will likely need to uninstall the dishwasher to access the pressure switch for testing. Here are the basic steps for uninstalling a dishwasher:

  • Shut off the power to the dishwasher to avoid electrical shock while you’re uninstalling the appliance.
  • Next, unthread the water supply line from the inlet valve (be prepared for some water to spill out).
  • If the dishwasher is hardwired, unthread the screw securing the junction box cover.
  • Unthread the wires nuts to disconnect the power wires and detach the grounding wire as well.
  • Remove the power cord wire strain relief nut so you can detach the power line from the junction box.
  • Disconnect the drain hose from the sink drain or garbage disposer and feed it through the cabinet.
  • Unthread the mounting screws securing the dishwasher’s mounting brackets to the countertop, cabinet, or floor.
  • You may need to raise the front leveling legs to lower the appliance.
  • You should now be able to pull the dishwasher away from the cabinet gently.
  • If the pressure switch is located directly under the sump, carefully tip the dishwasher back so it rests on its rear panel. Otherwise, you should be able to lift up the insulation to locate the switch attached to the frame.

Uninstall the pressure switch and tube for best testing results

For best testing results, both the pressure switch and the air pressure tube should be uninstalled. To do this, disconnect the wires from the switch’s terminals then detach the switch from the frame or sump (you can usually just rotate the pressure switch a quarter-turn to remove it). The air pressure tube should be detached from the sump port, but keep it attached to the port on the switch.

Confirm the air pressure tube is undamaged

Before you attempt to test the switch, you should confirm the air pressure tube has no cracks or holes in it and the tube fits snugly on the switch port. If you spot any damage, you should immediately replace the tube – that damaged tube could be the cause of your problem.

Dishwasher pressure switches will normally have three terminals

Understanding the function of the pressure switch’s terminals is important information to have before you can properly test the switch. Dishwasher pressure switches will normally have three terminals: a common terminal, a normally open terminal, and a normally closed terminal. The normally closed terminal provides power to the water inlet valve while the normally open terminal provides power to the appliance’s motor. You should use the dishwasher’s wiring diagram to correctly identify where the common, normally open, and normally closed terminals are located on the switch you’re testing.

5 steps to test a dishwasher pressure switch

With the pressure switch and tube removed or isolated from the dishwasher and the multimeter at hand, you’re ready to follow the five steps to test the switch for appropriate electrical continuity:

1) Rotate the multimeter’s range selection dial to the lowest setting for ohms of resistance.

2) Contact the black meter lead to the pressure switch’s common terminal and the red meter lead to the switch’s normally closed terminal. The meter display should indicate close to zero ohms of resistance.

3) Now blow into the attached air pressure tube. You should hear a clicking sound and the meter display should indicate the common terminal and the normally closed terminal no longer have electrical continuity.

4) Leaving the black meter lead on the common terminal, move the red lead to the normally open terminal. The meter display should show no continuity between the two terminals.

5) Once again, blow into the attached air pressure tube. The meter display should now show close to zero ohms of resistance until you stop blowing and the air pressure is depleted from the tube.

If the pressure switch tests negative for electrical continuity throughout the test, or positive when it should not, you’ll know the switch is defective and will need to be replaced with a new one.

Dishwasher Pressure Switch Testing

Use only genuine OEM dishwasher parts for the best repair results

So, has your testing confirmed the dishwasher’s pressure switch is faulty? Then your next step is to locate the right replacement switch for your dishwasher. You can find the exact pressure switch you need at Repair Clinic by entering the appliance’s full model number in the website’s search bar. The resulting list will be every compatible part that is replaceable on your dishwasher. From there, select “Switch” using the “Part Category” filter and “Pressure Switch” using the “Part Title” filter to identify the specific part you need to fix the water problem on your dishwasher. For the best repair results, you should only use genuine original equipment manufacturer (OEM) parts… and that’s the only kind of parts Repair Clinic sells, from such well-known dishwasher manufacturers as Bosch, KitchenAid, Kenmore, Maytag, Samsung, GE, Frigidaire, LG, Whirlpool, and many others.

Free dishwasher repair help from Repair Clinic

In addition to quickly shipping out genuine OEM replacement parts, Repair Clinic also wants to empower both professional technicians and do-it-yourselfers with free repair help: thousands of procedural videos, step-by-step guides, and product schematics accessible via the website’s “Videos & Articles” library. It’s there that you’ll learn the proper way to replace a pressure switch on a Frigidaire Dishwasher (model FPHD2491KF1) or find out how to install a new water inlet on the Whirlpool Model WDF520PADM7 Dishwasher. Explore some of this free content today and discover why so many techs and DIYers consider Repair Clinic as their repair partner.

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