You can usually hear the sequencers click and the elements hum when they kick in. Some trane/American std. used a contactor instead of sequencers. It's just a heavy duty relay, they make a click when they pull in also. You could also put an amp clamp on one of the wires feeding the heater at the breaker in your service panel to see if it's pulling amps with no blower. Each element pulls about 15-20 amps when energized. Many times you'll have more than one breaker feeding your heater, so male sure all the power is off before you reach into the furnace controls.