Well
after switching on the FT1000 the 2200 Microfarad C is empty and a
loading-current flow from the 13V source via the fan-Motor, via the diode into
the capacitor. This current is strong enough to start the motor running. When
the Capacitor is charged only the 220 Ohm Resistor limits the current through
the fan-motor. His speed and noise is reduced. Maybe you must change the value
of this resistor due to the "mechanical wellness" of the fan motor and the noise
you can accept for continues running.
By the way, the diode make sense for when the sensor in the PA-Unit switch to
ground. This diode protects the switching-transistor from the discharge-current
of the electrolyte condenser.
Put
all things together, specially take care of the fan by remounting it to the
PA-Unit (easy running and no cable around)!
Here
in my rig it works well. Cooling fan is running at low speed and low noise
continuously. On TX sometimes after long TX-time the fan switched up to his
maximum speed and falls down to slow operation after RX is in use.

No
warranty of function for this modification. I am not responsible for malfunction
of your equipment after doing this modification. Guenter DD9ZO Germany