If your dryer runs, but does NOT heat, you have a problem in the heating circuits. Any one of the following could be causing your problem:
1. Heating Element
2. Thermal Cut-Out (TCO)
3. Hi-Limit Thermostat
4. Improper input line voltage
5. Defective power cord.
The following link gives some advice on how to troubleshoot an ELECTRIC dryer with a no heat problem:http://www.fixya.com/support/r3576548-dryer_runs_but_does_not_heat
First, begin by unplugging the dryer and verifying the voltage at the wall receptacle. You should read 220-240VAC across the two Hot terminals (left and right slots). If the voltage is incorrect, check to make sure you don't have a breaker tripped. Some homes use 2 separate 120VAC breakers to provide power to the receptacle vice using one 240VAC breaker.
If the voltage IS correct, leave the dryer unplugged and remove the cover plate on the terminal block in the back of the dryer (this is where the power cord is installed). Plug the dryer back in and take a voltage reading across the two hot (RED and BLACK) wires at the terminal block. You should read 220-240VAC. If the voltage is good, you have an internal heating problem. If the voltage is bad at the terminal block, but good at the receptacle, you have a bad power cord.
NOTE: If the wires at the terminal block are not color coded, the outer two wires (left and right) are the hot leads. The center conductor is neutral or ground.
The reason a dryer will still run if the input voltage is incorrect, is because the drive motor only uses a portion of the 220 service. The motor runs off 110-120VAC, while the heating circuits require 220-240VAC. So, if you are missing 1/2 your input voltage due to a tripped breaker or bad power cord, your dryer may exhibit these symptoms.
If you determine the problem to be internal, the heating circuits are located in the rear of the dryer on the right hand. Just remove the back panel of the dryer for access.
The Heating Element is located inside a heater box. The Thermal Cut-Out (TCO) will be located on the outside of the heater box on the end opposite the heating element terminals. The Hi-Limit Thermostat will be located adjacent to the heating element terminals.
If either the TCO or Hi-Limit Thermostat are determined to be bad, replace BOTH components at the same time. That is why these components are commonly sold as a set. Failure to do so may result in premature failure of any parts you replace.
Replacement parts (if required) can be found at the following websites:
The average cost of these components varies, so shop and compare. The first three websites I listed also have helpful exploded view parts diagrams that can help you locate and properly identify the parts you need.
NOTE: In many cases the problem is NOT the heating element. The heating element has protection devices that are designed to regulate the heat temperatures. If the dryer overheats the Thermal Cut-Out (TCO) typically will blow BEFORE the heating element. The replacement kit is much cheaper than purchasing a new heating element that may or may not be the problem.
Read through the information I provided and, if you have any questions, please post back with your complete MODEL NUMBER and let me know. I hope you find this information is helpful.
NOTE: The door switch is a separate issue. You are right in your assumption that the switch is bad and needs to be replaced. However, a switch that stays on would normally cause the dryer to, not only run, but continue to heat.