This is the standard THERMOFLEX™ double circuit, Normally Closed (N/C) contacts detector, in which the connectivity is modified with pigtail leads that extend through a seal plate.This provides for enhanced protection against corrosive or moisture-laden environments. The model number suffix  “-2C”, indicates that the detectoir is a double circuit with two (2) sets of Normally Closed (N/C) contacts.  Each set of contacts is provided with 2 fly leads (pigtails). For each set, one blue lead connects to one side of the contacts and one blue lead connects to the other side of the contacts.
This detector is suitable for use in areas where condensation or corrosion couldn have harmful effects on circuit wiring connected to standard terminals. Its seal plate (with extended pigtail leads) will mount onto a typical cast exterior back box or standard 4-inch octagon box.The detector is connected to a fire alarm system’s input circuit as an initiating device.The internal contacts are normally closed, and will open when the detector operates either on a rate of temperature increase, or if the releasing temperature is reached. With its non-metallic diaphragm, the detector can operate normally at low temperatures, making it suitable for non-heated or chilled environments including garages and carports.
The second set of N/C contacts are used to activate a local ancillary function that includes elevator recall, release of magnetically-held doors, local signal operation, local annunciation, etc.  In many cases this set of contacts will be connected to a controlling relay that is used to switch heavier voltages.

Combination Rate-of-Rise & Fixed Temperature

The Model Number prefix “CR” indicates that the detector is a combination Rate-of-Rise and Fixed Temperature,(often referred to as “Dual-action”), unit.  The Rate-of-Rise function allows the detector to open both sets of its contacts when the temperature at the ceiling increases at a rate of 8.4 Celsius degrees (15 Fahrenheit degrees) per minute.  In most cases, the opening of one set of contacts initiates the Fire Alarm sequence.  The second set of N/C contacts is commonly used to initiate an ancillary function. The Fixed Temperature portion consists of a spring-loaded plunger held in place by a eutectic solder that will fuse at the specific temperature (in Fahrenheit degrees) as indicated by the Model Number i.e. 135,165,200 and 285 degrees.
Fixed Temperature Only
The Model Number prefix “CF” indicates that the detector is Fixed Temperature Only, and will therefore not respond to a rate of temperature increase but will operate when the detector fuses at the prescribed (Fahrenheit) temperature as indicated by the model number, i.e. 135,165,200 and 285 degrees.  This detector is referred to as “Fixed Temperature Only, non-restorable”.