I'm lost.... we have a roper dryer h.duty large capacity model and the past 3 weeks we have been fighting with the thermostat for high limit heat blowing.. we have check all the wiring and cleaned out the vents and blower chambers.. all is clean and there is no air restrictions. the heatiing coils are in great shape and heat if we put the two wires together to check.. but after a load or two ( med load) the thermostat blows again... any suggestions... this is getting old...