An Hitachi AC thermostat that won't work can be incredibly annoying. There are a number of problems which the Hitachi AC thermostat can cause, including refusing to allow the AC to turn on at all and not letting it reach the programmed setting.
If your Hitachi air conditioning unit won't come on at all, then you should check the thermostat. Turn off the power at the wall before doing any investigation. Firstly, ensure that there is power to the thermostat, both by checking the wiring supply to it, and also by replacing the batteries. Try turning the power on again. If nothing happens, turn power off and proceed. The next thing to do is to check that the thermostat is clean, and that it is not faulty. The latter can be done by turning the power on, setting the thermostat, and watching as it goes through the motions.
Another major problem with a faulty thermostat is the temperature control. If you are finding that the Hitachi AC unit is making the room too cold, despite having programmed the thermostat to a suitable level, you need to check that the thermostat is working correctly. Firstly, use the Voltmeter to ensure that the right amount of voltage is reaching the thermostat. If not, then you can recalibrate it by removing the thermostat cover, locating the ampere, and setting it to the factory recommended setting, as described in the manual. An Hitachi AC unit will require the ampere setting found at the last stage of the manual's instructions. Another problem may be that the thermostat is not level, causing the temperature gauge inside to be misaligned. Use a level to check the alignment, and adjust it if it is out of sync.
Dirt in the Hitachi AC thermostat is one of the most common causes of problems, so a good troubleshooting method is to just clean the thermostat. First, ensure the power is turned off, and then remove the cover of your thermostat. Locate the bimetal coil inside, and brush it free of dust using a soft brush, such as a shoe polish brush. Unscrew the body of the thermostat, and brush off the top and the mounting plate. Use a piece of cleaning paper, known as bond paper, to remove any dirt between the contacts. Check that there is no dust and debris on any other part of the thermostat, and then reinstall.