hvac - Correct Wiring for Furnace Blower Motor - Home After getting my furnace blower motor replaced, it now runs only in the following scenarios: 1. Mode "Cool" Fan "Auto" 2. Mode "Cool" Fan "On" 3. Mode "Heat" Fan "On" In other words it will not run when in "Heat" mode with Fan "Auto". I believe it could have something to do with the way the motor is wired. Blower Motor Wiring (colors) - Google Groups Blower Motor Wiring (colors) Showing 1-45 of 45 messages. Blower Motor Wiring (colors) Bill: 7/28/99 12:00 AM: Hi: I have a furnace blower that I plan to use just as a high powered fan. It's a rather small squirrel cage direct drive blower. I am assuming that the black wire is hot, How to Set Furnace Blower Speeds | Hunker If the furnace blower is having problems, though, changing its speed could make a difference in the furnace's performance. Most furnaces have a target speed, depending on the climate and the furnace's capacity. Consult your blower's owners' manual to determine what your furnace blower's speed should be.