At least once a year, it is a good idea to check your digital thermostat and make certain that everything is properly adjusted. It only takes a few minutes, and the benefits are a more energy efficient HVAC system that lasts longer and runs stronger.
Remove the Thermostat Face
Pull the face off the thermostat. On most units the face will either snap on, or twists into a locking base. Older model may have screws or clips that hold the face in place, but these are becoming increasingly rare. In fact, if you have one of the old screw mounted types, you may want to consider replacing it. Chances are good that doing so would improve your HVAC efficiency dramatically.
Adjust the Mounting Screws
Loosen the screws which attach the mounting plate. Using the torpedo level, make sure that the mounting plate is level, and then tighten the screws back down. If the plate is unlevel, it will have a very pronounced impact on how accurate the thermostat is.
Clean the Contacts
Using the small brush, clean all of the contacts and connectors to remove dust. If you hve one available, use an electronics vacuum such as that used to clean computer parts, and thoroughly clean the electrical parts of the thermostat. Dust can interfere with proper operation of the contacts, and may even cause the calibration to become unstable.
Calibrate the System
Using a small flathead screwdriver, adjust the bi-metal coil to match the actual room temperature. This coil is mounted a single small screw and should adjust easily. It only takes a very small adjustment to make a difference, so be careful not to over-adjust. Never completely remove the screw completely.
Adjust the Anticipator
If it seems as though the heater either runs overly long or doesn't come on often enough, you probably need to adjust the anticipator. This will either be another small screw adjustment, usually with an arrow or notch to mark the current setting, or a simple sliding contact. adjusting the anticpator to a higher setting will increase the time the heater runs when it comes on, and adjust in the other direction will cause it to run for shorter periods. This adjustment may have to be made a few times before the correct setting is found.
Notes on Troubleshooting
If the HVAC unit does not seem to be operating at all, you can check it fairly easily. Bypassing the thermostat requires removing the wires, and using a jumper to connect first the Red wire to the white wire, and then the red to the yellow (or blue) wire. White controls the heater operation and yellow or blue controls the cooling apparatus. If both units operate when powered directly, the thermostat has probably gone bad and should be replaced. Be sure to connect the wires to the correct connectors when you have completed the tests or repairs.