Having problem locating problem on unit under house. It will run great all day it cycles on and off normal i set the thermostat on 70. so i go to bed and wake up 3:00 a.m. to a burning smell really strong.i just had the blower motor replaced last season. there is no dust on the elements. it wont even put heat out now just cold air even when i put it on emergency heat. I am not running the unit right now I am using space heaters..i need to fix this my self i cant afford to pay anyone to come out and fix it...How can pin point the problem?