How to interpret diode-mode readings from a multimeter
Your description sounds exactly like a full wave bridge rectifier.

A multimeter in diode mode usually displays the voltage drop measured across the diode under test, as a small current is passed through it.

A single silicon diode usually has a forward bias voltage drop around 0.7V, so your reading of 500 to 700 probably corresponds to 500 to 700 milivolts.

When you measure across the AC input, you'll be measuring 2 diodes in series, plus the series resistance of the motor winding. Your measurement of 1200 to 1400 mV still makes perfect sense.