How to Identify and Wire a Heat Cool System - 1 Heat 1 Cool Furnace with A/C

In this video I try to explain how to identify and wire a "heat cool" system. This particular unit is a 80% furnace with an air conditioner. This type of system should still be fairly easy for an HVAC technician. A lot of techs still wire in the "G" wire going to the outdoor unit (for some reason) . They see terminal blocks on a furnace board that have letters next to them and they 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. (Think your way through it using what you have learned). Once you have that figured out you can pick the proper thermostat and start making things work! In order to save time, I will add to this later by posting a troubleshooting video on the same unit. See other videos for Fan and Heat sequence of operations. Here is how I would put the Sequence of Operation for this unit (generically speaking): Cooling Mode 1. Power “ON” 2. Thermostat is in the “COOL” position. 3. Thermostat senses a rise in room temperature above the set point. 4. The thermostat initiates a “Call for cooling” and the switches from “R” to “G” and “R” to “Y” closes. (24 Vac passes across “R” to “G” and energizes the Indoor Fan Relay Coil, 24 Vac passes across “R” to “Y” and energizes the Contactor Coil) a. The switches on the I.F.R. react and do the opposite of their normal position. (The N.O. switch close, The N.C. switch open). At the same time, the N.O. switch(es) on the contactor close. 5. The high voltage power passes through the N.O. switch(es) that has just closed and powers the Indoor Fan Motor. At the same time, the high voltage power passes through the N.O. switch(es) that has just closed and powers the Compressor and Outdoor Fan Motor. 6. If the motors are good then the motor turns “ON” 7. Thermostat senses a fall in room temperature so that the set point is met 8. The thermostat stops “Call for cooling” and the switches from “R” to “G” and “R” to “Y” open. (24 Vac stops passing across “R” to “G” and de-energizes the Indoor Fan Relay Coil, 24 Vac stops passing across “R” to “Y” and de-energizes the Contactor 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). At the same time, the N.O. switch(es) on the contactor open. 10. The high voltage power stops passing through the N.O. switch(es) that has just opened and stops powering the Indoor Fan Motor. At the same time, the high voltage power stops passing through the N.O. switch(es) that has just opened and stops powering the Compressor and Outdoor Fan Motor. 11. The motors turn “OFF”