HVACR214 – Electrical for Oil

1. HVACR214 – Electrical for Oil Stack Relay

2. Stack Relay • The stack relay is an older type of primary control that will trip if no flame is detected upon a call for heat. • The stack relay senses temperature, not light. >

3. Stack Relay • A bi-metal sensor sits inside the furnace flue (exhaust) pipe. When the furnace heats up it heats the element. • (refer to the stack relay handout) >

4. Stack Relay • As the elements start to move it sequences the contacts. >

5. Stack Relay • Shows the relay de-energized. The cold contacts are mid-seated and the hot contacts are open. >

6. Relay De-energized

7. Stack Relay • Thermostat comes on, energizes 1k and closes 1k1 and energizes the ignition sequence. • Also energizes 2k and 1k2 to close 2k1. This energizes the oil valve and the burner motor. >

8. Call for heat

9. Stack Relay • /R closes on the thermostat energizing te 2k and 1k relays, the SS heater , 1K coil and 2K coil. All use 12 volts. • The burner is now energized as well. • As the flame heats up the flue pipe the bi-metal in the stack relay starts to move as well. • This will sequence the hot and cold contacts. >

10. Warm Up

11. Stack Relay • As the bar starts to move the heat from the burner starts to move the cold contact and stops the SS heater from heating. • The cold contact has moved away from the SS heater circuit meaning that the flame has been established and lockout is not present. • Safety switch stays closed. >

12. Stack Relay • Shows interrupted ignition. Once the flame is established the ignition transformer drops out. • When the hot contacts close the cold contacts are completely disengaged de-energizing the 1K relay (ignition transformer). >

13. Primary Hot

14. Stack Relay • Shows the control tripped out on a no-flame condition. • The heater got hot as the contacts never sequenced to take it out of the circuit. >

15. No heat sensed off on safety