Dirty Dispenser Cup

• The detergent dispenser in your dishwasher can only dispense properly if it is clean before you begin the load. For this reason, always check the dispenser cup before adding detergent to ensure it is clean. Hardened detergent residue left behind from a previous cycle will not empty into the dishwasher. Food or liquid spilled into the cup will make powder detergents clump, causing some to remain behind when the cycle is finished, so load the dishwasher before adding your detergent.
  
  

Damp or Old Detergent

• Powder detergents will eventually become stale, particularly when they are not sealed properly or stored in damp areas. This causes the powder to become moist and to clump. If it is clumped together or stale, it won't perform as it should, and you may find that not all of the detergent empties from the dispenser cup after a wash cycle. Before filling the dispenser cup, shake the detergent container. If it has clumped or appears moist, throw it away.
  
  

Water Temperature

• Dishwashers require water that is at least 120 degrees Fahrenheit to dissolve dishwasher detergent properly. To test the water temperature, turn on your hot water faucet and let it run for a minute. Hold a meat thermometer under the stream to check the temperature. If it is not running hot enough, adjust your hot-water heater so that it is.
  
  

Spray Arm Blocked

• If the spray arms on the bottom of your dishwasher are blocked or clogged, then the water cannot reach the detergent dispenser, resulting in detergent left behind in the cup. Use a pipe cleaner to clear away any debris that may be clogging the holes of the spray arms and when loading, make sure to follow the manufacturer's guidelines to prevent blocking the spray arms with your dishes.
  
  

Malfunctioning Time Switch

• Some dishwashers have a time switch, which opens the detergent and rinse-aid dispensers. If your dishwasher is not emptying either of these after the cycle has completed, then your time switch may not be sending the signal as it should. The time switch should be repaired by a qualified technician.