We have RTUs with the board on the relay, the back side of the board the male push on terminal solder connection breaks. Sometimes just pulling the cover off will start / stop the fan. A little flux on the terminal, bit of solder on solder iron tip, and just touch the solder connection, as soon as it melts pull off. Do all of them as you can't see which one is broken. Don't forget to clean the flux off!!
Consulting the schematic would have made troubleshooting this issue easier. No voltage at contactor coil... find the contactor coil on the schematic and check for voltage on each point you trace on the schematic all the way back to the contactor. There should be nothing mysterious about how a unit operates if a good schematic is available.
When you work on larger equipment or unfamiliar equipment, a good schematic is priceless. You may have a huge control section full of components you don't recognize and over a hundred terminals. Without a schematic, diagnosing a problem as simple as a bad relay could take many hours. With a schematic, and you've got it figured out with 5-10 checks with your multimeter.