My whirlpool estate dryer will not heat. I have tested all the fuses and heating element and it is all good. I thought it was the timer and I replaced the timer. Dryer still will not heat when I turn timer and turn it on. It will heat when I pull up on the timer knob and if I look behind it I see a spark behind the timer and the heating coils will momentarily come on. the dryer will spin and turn but it blows cold air.