http://www.ehow.com/info_12203962_check-dryer-thermistor. How to Check Dryer Thermistor eHow
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.
The heating elements are located inside the heater ducts. If you think a heating element is faulty, test it with avolt-ohm-multimeter (VOM)set to the RX1 scale. Disconnect the leads from the power terminals and clip one probe of the VOM to each terminal. The meter should read about 12 ohms. If the reading is higher ohms, the heater is faulty and should be replaced. Replace a faulty heater with a new one of the same type and electrical rating. A heater connected to a 115-volt line usually has an 8.4-ohm resistance; a heater connected to a 220-volt line usually has 11 ohms resistance.
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,
OR you may have a broken centrifugal switch in the motor because this switch activates the motor and the heater as well. supposed to be if the motor does not run , the heater should not heat in order not to create fire but if the motor is not running, and the heater is still heating, then there could be a problem with the motor centrifugal switch that is connected to this interlock switch that should trigger the heater.
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 9 this is why in some cases the dryer will operate at lower cycles like gentle or low heat but not at higher settings?)
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.
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Dryer venting issues slow drying, fire flare ups, to hot, noise and clothes ripping etc
A lint filter that is full of lint will restrict airflow and lengthen dry times.
A blower wheel that is not firmly attached to the drive motor can slip and therefore not move air fast enough to properly dry clothes or even reduce airflow to the point where the high limit thermostat may trip and turn off the heat circuit.
In gas dryers, defective gas valve coils can create a symptom of taking too long to dry if they are intermittent. Check for proper flame ignition for the complete dry cycle to determine if this may be the cause.
The drum seals are used to prevent excess air from entering the dryer drum and act as a cushion between the drum and the front and rear bulkheads. The drum seals are made up of a felt like material. If the seal is torn or is worn then clothing can become stuck in the gap when the drum is turning. This can produce a scraping or thumping noise and the clothes can also be ripped and/or have black marks on them.
DOOR SEAL When the door is closed in gas and electric dryers the door seal helps to keep cooler air from entering the drum.
The vent tube or line itself. If it is kinked, smashed, to long, or filled, clogged with lint build up it can not only cause slow dry times but create a fire safety hazard. Try to stay away from using plastic or flimsy cellophane venting, aluminum is best!
To provide better air flow and heat dissipation try the following
Note the length of your dryer vent is a determining factor in how efficient your dryer will perform. If the total length of your pipe exceeds 25 feet then your dryer simply won't be able to perform as should, especially if your pipe runs vertically and through the roof. This is where a booster fan is sometimes needed. Booster Fans provide the extra push of air to exhaust the moisture and lint to the outside. These fans operate only when the dryer is activated, this is done by sensing the air flow through the pipe by a pressure switch mechanism or an electrical sensing relay which in turn activates the booster fan blower. I personally try to avoid adding booster fans simply because they are usually placed in a crawl space or attic and are therefore "Out of sight and out of mind." What I mean is... the unit could malfunction and you would never be aware of it. The result would be a restriction in the pipe which would cause a build up of lint at the fan. In addition, it's recommended that lint traps be placed before the fan itself which has to be cleaned out frequently. These can also easily be overlooked.
