In this video I try to explain how to identify and wire a "heat only" system. This particular unit is a electric furnace with a 5 KW kit. It is about as easy as it gets as far as low voltage wiring for an HVAC technician. So many technicians that I see will mistakenly wire in "circuits" that aren't needed. They see all these wires in the thermostat wire sheathing and just go crazy wiring what they have memorized on a white board. You have to be able to identify what unit you are working with in order to know what terminals/circuits are involved. Once you have that figured out you can pick the proper thermostat and start making things work!

In order to save time, I will try to add to this later by posting a troubleshooting video on the same unit.

Here is how I would put the Sequence of Operation for this unit (generically speaking of course):

Fan Only Mode
1. Power “ON”
2. Move “Fan” switch from “Auto” to “On” (the switch from “R” to “G” closes)
3. 24 Vac passes across “R” to “G” and energizes the Indoor Fan Relay Coil
4. The switches on the I.F.R. react and do the opposite of their normal position. (The N.O. switch(es) close, The N.C. switch(es) open)
5. The high voltage power passes through the N.O. switch that has just closed and powers the Indoor Fan Motor.
6. If the motor is good then the motor turns “ON”
7. Move “Fan” switch from “On” to “Auto” (the switch from “R” to “G” opens)
8. 24 Vac stops passing across “R” to “G” and deenergizes the Indoor Fan Relay Coil
9. The switches on the I.F.R. react and go to their normal position. (The N.O. switch(es) open, The N.C. switch(es) close)
10. The high voltage power stops passing through the N.O. switch that has just opened and stops powering the Indoor Fan Motor.
11. The motor turns “Off”


Heating Mode – Electric Heat
1. Power is “ON”
2. Thermostat is in the “HEAT” position.
3. Thermostat senses a fall in room temperature below the set point.
4. The thermostat initiates a “Call for heating” and the switches from “R” to “W” closes. 24 Vac passes across “R” to “W” and energizes the Heat Relay Coil.
5. The switches on the Heat Relay react and do the opposite of their normal position. (The N.O. switch(es) close, The N.C. switch(es) open)
6. The high voltage power passes through the N.O. switch(es) that has just closed and powers the Electric Heat Strip. At the same time, high voltage power also goes into the N.C. switch on the Indoor Fan Relay.
7. If the electric heat strips are good then they turn “ON”, If the fan motor is good, then the Indoor Fan Motor is “ON”.
8. Thermostat senses a rise in room temperature so that the set point is met.
9. The thermostat stops “Call for heating” and the switches from “R” to “W” open. 24 Vac stops passing across “R” to “W” and deenergizes the Heat Relay Coil.
10. The switches on the Heat Relay react and go to their normal position. (The N.O. switch(es) open, The N.C. switch(es) close)
11. The high voltage power stops passing through the N.O. switch(es) that has just open and stops powering the Electric Heat Strip. At the same time, high voltage power also stops going into the N.C. switch on the Indoor Fan Relay.
12. The Electric Heat Strips and the Indoor Fan Motor turn “OFF”