cloth dryer is a simple machine...make sure blower is running in full speed.and hot air circulates into the drum and out to the exhaust pipe, the air passage in the exhaust pipe must be free from any blocking for air flow...if you see hot steam in the machine, then must be the hot air not circulate, so make sure the hot air can move freely, take a look the picture.
http://www.google.ca/search?hl=zh-CN&q=dryer+machine+troubleshooting