A diagnostic system for an HVAC system includes a number of sensors used to
measure the operation of the HVAC system. Sensor readings are measured by
timing the delay between when a strobe signal is sent to a sensor and when
an interrupt signal from the sensor is received. A device driver used to
measure the sensor readings stores the sensor readings in pseudo-character
device files, which are universally accessible by different subsystems of
the diagnostic system. Based on the readings from these sensors, this
diagnostic system is able to determine the operational status of the HVAC
system and if an economizer in the HVAC system is operating properly.
