Here are some excerpts from the Passport I/O Controller Owners Manual:
The standard temperature sensor is integrated into the Passport Control Panel so the mounting location is important.
INSTALLING THE DISPLAY PANEL CHOOSING THE LOCATION Before mounting the control panel, consider the location. The display panel’s built-in air sensor provides excellent room-air temperature sensing when properly located and installed. For air sensor location see item 6 in Figure 1, page 3. Mount the display panel on an inside wall, slightly higher than mid-height of the cabin, in a location with freely circulating air where it can best sense average temperature. Its distance from the air conditioner must be within the 15’ (4.5m) length of the display cable (custom lengths available). Do not mount the display in direct sunlight, near any heat-producing appliances or in a bulkhead where temperatures radiating from behind the panel may affect performance. Do not mount the display in the supply-air stream. Do not mount the display above or below a supply-air or return-air grille. Do not mount the display behind a door, in a corner, under a stairwell or any place where there is no freely circulating air.
Passport I/O Control Operations Manual Mounting the Display
L-2231 ENGLISH 5
If you can not mount the display in a suitable location for accurately sensing room temperature, install the optional remote air sensor.
REMOTE AIR SENSOR Install the optional remote air sensor if the display can not be mounted in a proper location for accurately sensing room temperature. Installing the remote air sensor overrides the display’s built-in sensor. The standard cable length for the remote air sensor is 7 feet (2.1m). 1. Mount the remote air sensor in the return-air stream behind the opening of the return-air grille. 2. Plug its cable (6-pin connector) into the “ALT AIR” socket #J4 in the upper-left corner of the circuit board.
You can calibrate the temperature sensor and display by changing the system programming like this:
USING PROGRAM MODE ENTERING PROGRAM MODE You can only enter Program Mode from the Off Mode. If necessary, press the Power button to enter Off Mode. Press and hold the Power button while in the Off Mode until the letter “P” appears in the display. The characters “P1” followed by the P-1 parameter setting appear in the display. The control is now in the Program Mode. If no programming is attempted for one minute, the control exits Program Mode and returns to Off Mode.
P-5: Temperature Calibration This feature calibrates the ambient sensor within a range of ±10°F. Adjust this parameter to display the correct room temperature reading.
You might want to become familiar with that manual. There are a number of useful and important things to learn about the system that can be controlled by programming.