PTC Element (Positive Temperature Coefficient)

Fig 1: Identifying PTC Element

Courtesy of VOLVO CARS CORPORATION

A diesel engine has optimal efficiency and therefore generates very little surplus heat. On some markets with a cold climate the vehicle uses a diesel engine with a PTC element as an extra heater.

Even four cylinder engines, in some cold markets, use a PTC element. The PTC element is also available as an option.

The PTC element heats the passenger compartment quicker at lower outdoor temperatures. This is essential as the coolant does not emit sufficient heat, especially during the initial minutes after the engine has been started.

The PTC element is placed in the climate unit after the heat exchanger. It is accessible from the front.

The air that flows past the hot PTC element, on its way into the passenger compartment, is heated directly.

Typical characteristics of a PTC element:

fast heating directly after start
high degree of efficiency
lightweight, compact design
cannot be overheated
maintenance free.

Fig 2: Identifying Ceramic Plates And Radiator Elements

Courtesy of VOLVO CARS CORPORATION

The PTC element consists of small metal coated ceramic plates (1) sandwiched with radiator elements (2) of aluminum. These layers are held together in a frame (3) of a spring element. The aluminum element has the task of conducting current at the same time as it transfers heat to the air flow.

The maximum output of the PTC element is 1250W.

Fig 3: Identifying PTC Element

Courtesy of VOLVO CARS CORPORATION

The PTC element has a positive thermal coefficient. This means that the resistance value is relatively small at low temperatures and increases with the rising temperature.

When the cold PTC element is voltage fed, the current is high during the initial stage and heats up the element. With a rising temperature the ceramic's resistance value also increases whereupon power consumption drops.

It takes approximate 20 seconds until the stabilization current is reached. The ceramic temperature is dependent on the heat output and the ambient temperature. With good thermal dissipation the temperature drops and with that the resistance. This results in an increase in power consumption and with that an increase in temperature.

If a small amount of heat is emitted to the surroundings, the temperature of the ceramic rises and with that the resistance. Through this cycle the heating element is regulated with its own power consumption. The result is an equilibrium between the supplied electrical energy and the emitted thermal energy.

The Climate control module (CCM) controls, via the Central electronic module (CEM), the function of the PTC element.