The dryer is cutting off in mid cycle after running for about 15 min on high heat, no matter where the timer is. It seams to be getting too hot. I have installed a new vent and the lint catch is cleaned out. The unit is 4 years old. Also it will start back up instantly but will cut off again within about a minute. If you put it on a lower heat setting it will run a little longer.

I would suspect the control panel is defective.

there is a cycling thermostat in line with the high limit thermostat and timer circuit,on timed dry its disabled and the timer will run no matter what,on any sensor dry setting it uses the heat of the element to heat this cycling thermostat to move the timer as the clothes get drier as the heating element heats the timer doesn't move,when the heater cycles off from the high limit thermostat then timer moves again,you need to find out if its a bad heating element,thermal fuse or possibly even a circuit breaker in the homes electrical panel tripped out on one of the 2 phases that gives you the 240 volts required to operate the dryer element,the breaker may not show its tripped,so shut it off and back on and try this first

I think you are on the right track with a faulty high limit switch. When i serviced these units we always replaced the operating thermostat and the high limit switch together they came in a kit. The operating thermostat in theory should never let it get hot enough to trip the high limit switch, which is really just a safety backup for the operating thermostat. Get the kit and replace both, and also make sure your exhaust vent going outside has good flow at the outside vent,a restricted vent system will cause similar issues.. Good Luck

Hi and welcome to FixYa. I am Kelly.
No heat and the timer not advancing is usually caused by an open cycle thermostat. (Item 20) This link: http://www.appliancepartspros.com/partsearch/model.aspx?model_id=5151792&diagram_id=956658#d956658
It can also be caused by a defective high limit thermostat (Item 15 above link) and an open heating element item 17 above link.
Before you even try to take the dryer apart or attempt ANY repairs go to the main CB panel and cycle the dryer CB off by physically pushing the thermostat to OFF (manually resets CB) then back to ON, Test the dryer for heat. Sometimes one of the 2 breakers trips allowing the dryer to run but not heat.

You can download this job aid to assist in locating / replacing the failed part.
http://www.servicematters.com/tech_ref/catalog/pages1-27.pdf

Disassembly order is Top, Toe Panel and Front Panel. Make sure to remove the 2 screws in the lint filter befor attermpting to remove the top.

Make sure to unplug the dryer before attempting any repairs.

Testing of each thermostat is done at room temp with one terminal disconnected with an Ohm meter. They should read continuity (ZERO Ohms) across the 2 terminals.

The heating element should also read a very low resistance across the terminals.

Note item 18 in the first link. Heating element wires are notorious for getting hot and failing at the heating element connections.

I do not at this point think you have a timer problem. There is a very remote possibility that you could have a bad motor switch.

Also check all connections at the dryer cord terminal block connection. These are known to also get hot from a loose connection. See item 42 this link for wire kit to fix the terminal block wires
http://www.appliancepartspros.com/partsearch/model.aspx?model_id=5151792&diagram_id=950307#d950307 (Last item on the page)

Thanks for choosing FixYa,
Kelly

when was the last time you cleaned it out,try running it with the vent line removed,you need to clean out the duct that the lint filter slides into,vac out the inside of dryer where the motor is,if you have a shop vac put it on blow and blow off the motor and clean out the vent line and the outside vent,if the vent line is long i use a leaf blower to clean out the vent line,also is it gas or electric?next time send model number?if it's gas you could have bad gas coils,when they heat up they fail,clothes are warm at end of cycle.run the dryer for 15 to 30 minutes and check to see if the flame is still lighting if not bad gas coils.hope this helps

SOUNDS LIKE ONE OF YOUR HEAT SENSERS

It is possible your Cycling Themostat is not working properly. It determines at what temperature to turn heat on and off to maintain a consistent dryer temp. The High Limit Thermostat would turn off the heat but your dryer would still run. That leaves the Thermal Cut Off which is turning off your dryer. It might be faulty and turning off at too low a temp, or it might be doing it's job. In that case something else is wrong. If you can check the exhaust air temperature at the dryer, it should be under 175 degrees. If you are absolutely sure the vent is clear, then replace the Dryer Cycling Thermostat.

its your timer that needs replacment. not the thermal fuse.
if the thermal fuse was ever tripped, it would not start at all. you would only hear the ticking of the timer.
if other cycles work its the timer not any of the sensors or fuses.
dryers are very basic, and are completely controlled by the timer (or control board for digital models)

You have 3 thermostats. By the description of the problem it sounds like it needs a new high limit thermostat. All 3 thermostats and the heating coil can be checked with an ohm meter. Also check the ground on the heating coil. It could be grounding it's self out.

you have to change out the timer motor...
http://www.partselect.com/repair.aspx?appliance=dryer&part=dryer-wont-heat