If your dishwasher's rinse agent dispenser doesn't open during the wash cycle, your dishes will be clean, but they may have water spots. The Jet Dry dispenser door may be clogged with old detergent and rinse agent, keeping it from opening. There may also be a problem with the mechanism in the dishwasher door that triggers the opening of both the detergent dispenser and the rinse agent dispenser. There are two types of triggers, solenoid and bimetallic warp, but the process for testing and replacing the trigger is the same regardless of type.
Open the rinse agent dispenser, and clean the dispenser and the door with a wet sponge. Remove all the residue you can find. Open and close the Jet Dry dispenser door to see if it moves freely.
Cut off the power to the dishwasher by unplugging it, or turning off the power at the circuit breaker. Open the dishwasher door, and support it with your knees as you sit on the floor. Unscrew the screws around the door's perimeter that attach the door panel to the dishwasher door. Lift the door panel off the door, and set it aside.
Locate the solenoid trigger or bimetallic warp trigger on the door near the area that corresponds with the rinse agent dispenser on the door panel.
Detach the wire leads from the trigger. Set the volt ohm-meter to the lowest resistance scale, which is generally Rx1. Touch the volt ohm-meter's test leads to each other, and then to the trigger's exposed wires. If the ohm-meter's needle moves, the triggering mechanism is working. If the needle does not move, replace the trigger.
Unscrew the mounting screws that hold the trigger in place. Take the old trigger to a home improvement store to help you buy the correct replacement part.
Attach the replacement trigger to the dishwasher door using the old mounting screws. Reattach the lead wires, and screw the door panel back onto the dishwasher door. Plug the dishwasher in, or restore power at the circuit breaker.