Turn the key on with engine off. Check for 12 volts on the 85 and 86 terminals. You should get 12 volts on the hot side and nothing on the grounded side, because the heat sensor in the block is not grounding. After you determine which terminal is hot then ground the other terminal and listen for the relay to click. Use Caution because this should start the fan unless you unplug the fan harness.
If the relay clicks check for 12 volts between the 87 terminal and ground while the relay is engaged. If you get voltage then the fan is probably shot.
You can hot wire the fan with a ground to one wire and a hot wire to the other and the fan should run. You can also check the fan windings with an ohmmeter by checking continuity between the fan wires. If you get infinity then the fan windings are open.
Here's a diagram.
Yes cooling fan or heater fan?