Patent ID: 7836707

Claim:
A method of detecting and responding to a coil condition in an HVAC system, comprising: calculating an initial airflow restriction value of the HVAC system; calculating a current airflow restriction value of the HVAC system periodically during a cooling cycle of the HVAC system; comparing said initial airflow restriction value to said current airflow restriction value, wherein if said current airflow restriction value is greater than a first sum of said initial airflow restriction value and a restriction factor, then the coil condition is preliminarily determined to be freezing, and wherein if said current airflow restriction value is less than a first sum and a restriction factor the coil condition is determined not to be freezing and the HVAC system will continue cooling upon demand, with another current airflow restriction value being calculated periodically for comparison to determine whether the coil condition is preliminarily determined to be freezing or not; and stopping cooling of the HVAC system if the coil condition is preliminarily determined to be freezing; wherein if the coil condition is preliminarily determined to be freezing, a filter check is performed and a current filter check airflow restriction value is calculated, said current filter check airflow restriction value is compared to a routine filter check airflow restriction value calculated from a periodic filter check performed on the HVAC system, wherein if said current filter check airflow restriction value is greater than a second sum of said routine filter check airflow restriction value and a filter-scaling factor, then cooling of the HVAC system remains stopped, and wherein if said current filter check airflow restriction value is less than said second sum, then cooling of the HVAC system is resumed.