High voltage PTC heater, function

Location
The high-voltage PTC heater control unit (N33/16) is located in the front of the vehicle engine compartment and it is attached next to the high-voltage components above the electric machine 1 (A79/1).

D83.70-A007-76

 Interlock circuit
The interlock circuit serves to protect people against inadvertent contact with high-voltage components.
All plugs are contact protected.
The seating of all connector couplings is monitored by an interlock circuit.

Function requirements for high voltage PTC heater, general

 Automatic air conditioning activated.

High-voltage PTC heater function, general

The high voltage PTC heater control unit is used to heat up the coolant in the heating circuit for the vehicle interior.

With the functional principal of a continuous-flow water heater, the water for the heating is heated up by a PTC heater. The air for the vehicle interior is then heated up by the heater heat exchanger.

The high-voltage PTC heater control unit is actuated by the automatic air conditioning control and operating unit (N22/2) depending on the requested heat output. The heating elements are heated by energizing them. The coolant flowing past the high voltage PTC heater control unit absorbs the heat of the heating elements and is thereby heated up.

The circulation pump (M13/4) pumps the coolant from the high voltage PTC heater control unit to the heater heat exchanger thereby enabling the vehicle interior to be heated.

From a certain operating temperature of the high-voltage batteries (G1/31, G1/32, G1/33) and high-voltage battery 4 (G1/34) (with code E4T (High-voltage battery (47 kWh))), the refrigerant circuit draws heat from the coolant circuit of the high-voltage batteries through the evaporator/heat exchanger (low-temperature circuit 2) and makes this available to the vehicle interior heating circuit. As a result, the waste heat of the high-voltage batteries is used to heat the vehicle interior.

The heating output of the high voltage PTC heater control unit is automatically switched on or off steplessly and as needed. This enables the thermal energy of the high-voltage batteries to be utilized effectively, thereby preserving the energy balance of the high-voltage on-board electrical system.