The blower will not come on when I turn on the heat and the heat sensor keeps tripping the relay switch. Can you tell me what I need to do?

If the blower won't come on it sounds like either a fan relay on the board or a burnt speed (at least) in the moter. When it heats up it causes the limit switch to trip. If the blower coms on with the thermostat in fan ON instead of AUTO rune the fan and turn the heat on that way until you can get the moter checked out And check your filters if there clogged the unit will overheat also ( very very common )