Furnace Blower Motor Diagnosis and Repair

Note: the start winding is labeled incorrectly in the video. The start winding is the 6.2ohm leg on the bottom. See comments below for more detail. This video documents the diagnosis and replacement of a faulty blower motor in a Lennox furnace. 80MGF Series. When the air conditioning was turned on the fan did not blow air, while the compressor would run. There is a section that briefly explains how to use a volt/ohm meter to trouble shoot the motor, then that method applied to both the bad motor and the new motor. Then the video shows how to actually install the fan/motor assembly. Search for info on PSC (Permanent Split Capacitor) motor for more information. Info I found on RUN CAPACITORS. Helps if you know a little bit about AC circuits. *************************************************************************************************** ""Most smaller, single phase motors usually have a permanent magnet armature that is pushed / pulled around by the rotating inductive field produced by the stator (outside) windings. The inductive field rotates simply as a result of the positive / negative alternations of the 60HZ AC current flowing through the windings. The problem is that when the voltage is applied, the 60HZ is applied immediately, the rotation of the field through the windings begins immediately, and the armature has no chance to react (or catch up, as it were) to the field. The start cap provides that electrical "push" to get the motor rotation started. It does this by creating a current to voltage lag in the separate start windings of the motor. Since this current builds up slower, the armature has time to react to the rotating field as it builds up, and to begin rotating with the field. Once the motor is very close to it's rated speed, a centrifugal switch disconnects the start cap and start windings from the circuit. Watching a single phase motor starting you can see that this all happens very quickly. Without a start cap (such as when one burns up) when the voltage is applied, the motor will just sit and hum. But if you were to grab the shaft and give it a spin, the motor would (usually) start and run normally.""""