Thermostat Wiring Diagrams [Wire Installation] Simple Guide Thermostat Wiring Diagrams for Heat Pumps - Heat Pump Thermostat Wire Diagrams. Heat pumps are different than air conditioners because a heat pump uses the process of refrigeration to heat and coole an air conditioner uses the process of refrigeration to only cool, the central air conditioner will usually be paired with a gas furnace, an electric furnace, or some other method of heating. Guide to wiring connections for room thermostats At left the thermostat wiring diagram illustrates use of a Honeywell T87F thermostat in a 2-wire application controlling a gas fired heating appliance. In the Honeywell T87F thermostat series the single pole double throw switch makes (closes) one set of contacts when the temperature falls - to turn on the heating appliance. Problem: Fan Blower will not come on in the "On" position Dec 09, 2014Hello, I have a mid 90s Nordyne furnace. According to the wiring diagram it is a 2 wire hookup, red and white. However it looks like the previous owner added AC and added in a fan relay switch along with a 4 wire tstat. The AC was removed prior to us purchasing and we are just trying to get the heat working. How To Read York Hvac Model And Serial Number Rating: older York AC. size / from model number ? by: Ernie HI im trying to replace my old 1982 York condenser compressor unit its worn out and loud, but having trouble with understanding what size it is . the information tag is sun bleached out and very difficult to read . after trying to find out what the size is for a few hours. i was hoping that someone might know how or point me in the