[wbhoy1]

Replaced thermal cut off and high temp switch, lasted about two weeks. replaced again and lasted 2 loads. heating element tested ok. there is 115v on all terminals

[denman]

I do not have a wiring diagram for this actual unit so am doing some guessing.

heating element tested ok.
Did you check for a grounded element?

there is 115v on all terminals
This would be normal depending where the timer is set.
On most units the centrifugal switch on the motor disconnects one side of the heating coil. The timer disconnects the other side. So if the timer is set to a dry mode you will see 120 on all connections when referenced to Neutral (chassis)

You have to find out what caused it to go.
Note: that sometimes they do just blow on their own but changing it without checking other things is a gamble.

Check the heating coil.
Unplug the unit and both wires to the coil.
Check it with a meter, should be around 12 ohms.
Then check from each side of the coil to the case/frame, both should be infinite ohms (open). If not the coil may have sagged or broken and is touching the case. This can cause it to run on high and the thermostats cannot regulate it.

If the above is OK then you will also have to replace the hi-limit as it should have regulated the temperature so the fuse did not blow.

You still have to find out why it blew.
Check that the belt is OK.
Check the seals (drum etc) in the unit. The air is pulled over the heating coils, through the drum and pushed out the exhaust. So any large seal leak will pull in room air and the cycling thermostat on the blower will run the unit hot.
Check that the lint filter is not coated with fabric softener residue which greatly reduces air flow.
Check/clean your vent system.
Check/clean the blower wheel.

If all OK you may want to replace the cycling thermostat as it's contacts may not be opening (welded shut).