FIRST OFF IN THE AUTO DRY MODE THE DRYER USES THE MOISTER SENSOR AND AS LONG AS THE MOISTER SENSOR DOES NOT DETECT HEAT OR DRIED CLOTHES IT WILL CONTINUE TO RUN FOREVER.
NEXT AS FOR UR NO HEAT:
ELECTRIC Dryer no heat or little heat, or shuts down to fast:
Check your venting and lint basket. Check blower for lint build up and blower wheel obstruction., test by trying to turn the wheel manually by hand (should be easy) May have to remove cabinet or front/back plate to get to it)
Next check the heating element itself with a meter for continuity OHMS CLOSED CIRCUIT. If not its defective or has a short if its grounding out? Which in turns causes blown fuses or thermostats or overheating.
Check dryer Terminal block prongs both outside prongs should give combined 220, and 110 each if u check 1 outside & 1 center (ground) prong. Also check house electrical outlet for full voltage. 220 because if u only get half or 110 volts you will be able to run the machine which uses only 110 to run motor but not the heater which uses a full 220,
Check the thermal cut off, the cycling and the hi limit thermostats.
For continuity or OHMS. If no ohms or resistance they need replacement.
In some dryer's the control panel relies on a thermistor rather than a CYCLING thermostat to regulate the drum's air temperature by monitoring the component's resistance changes; resistance goes down as temperature increases and up when temperature decreases. Once the drum's air temperature reaches a certain level required to dry clothes, the control panel shuts off the heater. The panel will turn the heater on again and begin another heating cycle when the thermistor indicates that more heat is needed to keep the air temperature constant inside the drum
Lastly check your moister sensor. ( located inside the dryer door usually) Especially if machine seems to shut down early and clothes are still wet.
Test with a meter at room temperature and it should show continuity.
A failed moisture sensor will affect the dryer run time in the automatic moisture sensing cycle but it will not affect the heating of the dryer or the timed cycle. Which are reflected by the thermostats.
Read more :http://www.ehow.com/info_12203962_check-dryer-thermistor.html