Occasionally we are asked if we can test a mod motor. If it is a series 90 motor, it is very easy to test in the field with very few tools. All you need is a multi-meter and a couple jumper wires.
Step 1 - Remove all control wires from the R, B, and W terminals.Step 2 - Turn on the power and verify power to the motor using the multimeter. It should be 24 volts AC after the transformer (either built in or external).Step 3 - Attach a jumper wire between R and B and the motor should drive fully openStep 4 - Remove the jumper and connect between R and W. The motor should drive fully closedStep 5 - Attach a jumper between all three terminals R, B, & W. The motor should go to the middle of the stroke.