There are two speeds.  The low speed might not be noticable if you were not
specifically listening for it.  The high speed sounds like you started a
lawn mower.  There is a thermostat switch on the radiator.  Remove the wire
harness and jumper between the wires and if everything is working well
(except for perhaps the switch), you will hear the fan.  You can find the
two speeds by trial and error.  Tou cannot cause any damage by placing the
jumper in the "wrong" location.
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