I have a Marine Air Unit Model VTD16K – 410 that was installed last June. It has the Passport I/O compact control panel. 

The fan speed control function has never worked. The fan always runs at one speed, presumably high speed.  Although the control panel allows selection of automatic, or manual fan speeds 1 through 6 with the fan LED light illuminated if manual mode is selected, the manual speed has no effect on the fan speed. In addition, in automatic mode, the fan speed never changes as described in page 6 of the manual, Fan Modes.

Is there a programming change, or something that can be done about this?

The unit was purchased from the boat builder – Mirage Mfg Gainesville FL – who also installed it to replace an an Anchor unit with a burned out compressor (This unit burned out because the boat sat for five years with the AC in RH control mode, and no one ever checked it. After a few years the cooling line plugged up with barnacles, causing the compressor to continually overheat until it died. After the new unit was installed it got hot, tripping out on high pressure. We flushed the line out with Triton AC flush, and now it runs fine.) The guys that installed it were riggers, not AC technicians.

As a result of your post, I checked the P2 and P3 parameters. They were both set to the same number. I set P2 to 90 and P3 to 40. I also set P16 to SC. Now, it seems to work as advertized. Thanks