j1 on the adaptive defrost is power in, so you should have 120 v here or it wouldn't be defrosting, j11 is the power to the fan, during normal operation, this should have 120 v to run the fan... if your meter is showing you 120v then it's saying that between the two points your testing there is a 120 v difference, if the adc was operating properly your meter would read 0 since both lines should have 120.
to look at it a different way, try testing between j1 and ground, and then j11 and ground, you should get 120 between j1 and ground, and judging by your post you should get 0 between j11 and ground, this would be because the ADC is not sending power to the fan.
at this point if you want to double check before you replace the adc you could check for resistance between j11 and the connector on the fan motor, it should read a very low resistance and not read open ( the wire should be red with a white stripe) then you can confirm that you have a good neutral by reading resistance from the other wire on the motor to where it goes into the 6 pin connector on the backwall (it joins up with the neutral for the defrost heater, and since you say the heater is working we can assume that the wiring past this point is proved good)
lastly if your feeling game enough to try it you could always try jumping j1 to j11 with a wire... this would bypass the adc and force 120 v to the fan, if it runs, then that would also prove the rest of the wiring to be working properly.. I wouldn't recommend trying this unless your comfortable with it, and understand that if you touch bare wire while doing this you will get unpleasantly shocked... and this tells you nothing that testing the resistances won't tell you, it's just a faster way to test it...
hope this helps explain the process a bit better