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Testing Mod Motors

How to test an M91xx series 90 mod motor

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 open

Step 4 - Remove the jumper and connect between R and W. The motor should drive fully closed

Step 5 - Attach a jumper between all three terminals R, B, & W. The motor should go to the middle of the stroke.

If the motor behaves as described above, then the motor is good. If it doesn't then the motor is bad.

Did you know?

There is a cheesy way to remember which way the motor should go.

R to B = Really Big

R to W = Really Wittle