Theory Of Operation
WARNING: This page is about a different car, the 2014 Dodge Journey. However, it is still accessible from the selected car via links, so may be relevant.
Three relays are used for the electric Positive Temperature Coefficient (PTC) heater system. The PTC relays are used to switch fused battery voltage directly to the heating elements of the PTC heater unit when requested by the Powertrain Control Module (PCM). The PTC relays are activated through a ground path provided by the Body Control Module (BCM).