From the Manual:
Adjusting Fan Speed Manually
Press the FAN key to select manual fan control. The Fan Indicator will light to show that it is in the manual mode. Then use the SLOW and FAST keys to select the desired fan speed.
Note that you can use the manual fan control to circulate air even when the system is in the OFF mode.
Adjusting Fan Speed Automatically
Press FAN a second time to select automatic fan control. The Fan Indicator goes off. Now the system will automatically adjust fan speed as the actual
cabin temperature deviates from the setpoint. As setpoint is approached, the fan speed automatically slows. Once setpoint is reached, the
compressor
cycles off and the fan keeps running on low speed.
http://www.tropicalmarineairconditio...-0634-LP12.pdf