Newly acquired 2nd hand dryer. Symptom: long dry times. Cleaned lint trap & vent hose; opened back/lint chute and cleaned. Air flow seems good. Continuity tested for element & thermostat next to element cover. Tested with mostly dry load of clothes, selection = cotton + timed, door opened slightly with door switch depressed manually. Observed element turned on & glowed red for 6 sec, turned off for 50 sec, turn back on again for 6 sec. Air in drum only slightly warm. Suggest next troubleshooting steps?