The ST-FRE range of frost thermostats provide a switch output based on the average temperature detected along a two (6.56 ft) or six metre (19.69 ft) capillary sensor. A common application is for frost protection on fresh air intakes or airconditioning systems, to prevent the icing up of filters, fans and coils. The capillary is fixed in a matrix across the duct, in a position downstream of the pre-heater or frost coil.