I have a York central a/c forced air gas furnace. It's about 10 years old. The blower motor has stopped working. I can spin the squirrel cage freely by hand. Everything else seems to work as it should. Using a multimeter, as far as I can tell (I'm a plumber, not an electrician) 120V is not being sent to the blower motor. What's my next step?

The blower is controlled by a relay. Follow the colored wires from it back to where they go. A white wire should go to the incoming power. A relay usually has 4 contacts, power in, power out and 2 coil contacts. Power out should go to the blower. Power in comes from the power feed to the furnace. One side of the coil will be connected directly to a transformer, usually by a blue wire. Now the fun starts. The relay and the transformer too may be mounted on a control board. There are limit switches and timers to start the blower after the furnace and have it run after it shuts off. It may also work that way with the A/C. If the coil has 24V AC and power doesn't flow from the power in contact to the power out, the relay is bad. The old separate components were easier to replace than the little ones on a board. Otherwise, you are going to have to check out the limit switches and timers. If you find a schematic pasted to the furnace or in an envelop, it will be a big help. There should be a Y terminal on the furnace controls. One wire should run from it to the thermostat, and the other outside to the coil on the compressor relay. There should be internal connections to the switches and the blower relay coil.

Most furnaces have a switch that kills all the power when you open it up. That keeps you from electrocuting yourself when you change the filters. It also makes trouble shooting harder. Hold it closed, jumper it, etc. Just watch what you touch.

It could be a bad capacitor. If you can *carefully* give the fan a little push start when it tries to kick on and the fan then works correctly a new capacitor would be in order. But you said you didn't detect voltage so this is an outside shot.