Dryer turns on and rotates. However, does not dry clothes completely. Cycle signals wet,then damp,cool down and finally dry,but clothes are still wet. Sometimes the dryer works fine and completely dries the clothes in one cycle.

There are 3 steam cycles. See Page 42 of the manual. These cycles use steam so the fabric will have a degree of moisture.

...

A dryer moisture sensor can stop working without notice, until you notice your clothes being over dried or still wet at the end of the cycle. It is a good practice to test the dryer moisture sensor periodically. There are two types of moisture-detecting sensors for dryers. Once you understand how they work you will see how to test each one.
1. Sensor BarThese sensors contain digits that protrude outwardly. They work on an electrical current and the moisture from the clothing.
The first step to test is to place completely dry clothes in the dryer and turn on the dryer; it should run for a few moments and then shut down right away.
Secondly, place damp clothes into the dryer, turn on the dryer and watch the timer. As the clothes begin to dry the timer will move and shut off.
2. ThermostatThe timer is regulated by the thermostat. The thermostat rests in a closed position. To test this type of moisture sensor, place damp clothes in the dryer. Watch the timer; as the clothes begin to dry, the thermostat should open and the timer will move forward ,eventually shutting off.

sensor has wax buildup on it Dryer thinks clothes is dry. Shuts down. Get busy cleaning the sensor strips with windex or 409 The strips are located inside the dryer below the filter on most models. The way it works is wet clothes rub the sensor strips which discharges a capacitor on the dryness sensor board. As long as the capacitor is being discharged from the wet clothes the control knows to keep on a truckin. if no moisture is sensed then the capacitor will achieve a full charge and the control will proceed to end of cycle after a cool down period. Clean the sensor bars and party on.

If you need further help, reach me via phone at https://www.6ya.com/expert/dan_73bbd84fe1d95b61

If your dryer has electronic sensors like this:

They might have a coating builtup on them preventing them from feeling the wet clothes.As the wet clothes tumble in the dryer they rub up against these sensor strips. As long a wetness is there the capacitor is dicharged on the controls upstairs and it continues to dry them wet clothes. If junk gets on them sensors no wetness will e felt by them sensors. It is a simple as that. The dryer thinks the clothes is dry because no dampness is being detected so is shuts down thinking all is propah. Get some windex and scrub them sensors good so dampness can be sensed by the two sensors once more and party on!

If you need further help, reach me via phone at https://www.6ya.com/expert/dan_73bbd84fe1d95b61

Your Sensor that senses the clothes are wet or dry is shorted out. The dryer works likes this so the dryer heaters dont stay on while the clothes are dry. When the sensor senses the clothes are damp or wet, the heater stays on, when they start drying the sensor senses it and starts to turn down the heaters
http://tlc.howstuffworks.com/home/dryer6.htm

I am having the same problem on a WD9900A. The wash cycle works great. Spins fast and clothes are completely rung out. Dryer cycle heats up well. Fluffs and heats cloths. At some point during dry cycle water is injected on clothes and they end up sopping wet; much wetter than after wash. Filter is clear. Outlet pipe clear and functions well. Possible problem with dryer timer? Or washer timing kicking back on?

I'll take a stab that you use dryer softener sheets. These will deposit a coating on the two metal sensor bars (about 4 inches long, very near the lint filter inside the drum) which prevents the sensor from "seeing" that the clothes are still wet, so the dryer jumps to the cool down portion of the cycle. Clean the metal bars off and it should work again. (note: the bars are not in the cycle if you choose time dry instead of using the automatic cycles)

Time to check out and clean your filter...........

Problem solved! We read on here about someone else addressing the AF code by removing the back panel and fixing the pully that had come off. Belt was fine, with pully back in place dryer now works perfectly again. Thank you for saving us so much time and money!

is your dryer a conderser type
does it have a tank that you have to empty at the end of cycles
if it does the filter that condensers the water from drying cycle
if that is blocked it will not work