That diagram is actually for the Gas engine not the Diesel......the diagrams are similar and in either case have nothing to do with the AC Clutch Relay.
In the case of the Gasser, the High Speed And Low Speed Relays get their Ground power from the PCM and in the case of the Diesel these relays get their ground power from the ECM. The ECM gets its commands in this case from the BCM which gets its commands from the A/C switch panel and also High Pressure Switch for the Diesels only.... if there are issues with the refrigerant pressure.
Anyhow the problem in this case was that the Low Speed Relay was unable to send its +12 volt output to the Radiator Fan Motor due to its female pin being pushed back.
For future reference here is the circuit diagram for the relays for the Diesel....how the relays get their ground from the BCM or High Pressure Switch is pretty complicated though but here is also the location of the High Pressure Switch as well in case there are further problems.