Heating System

Heating System

Coolant Circuit, Schematic View:

The main coolant system supplies liquid at engine temperature to the heater matrix to provide heat to the vehicle interior. Unlike previous air blend/constant matrix temperature systems, in-car temperature is now controlled by mixing recirculated coolant in the heater circuit with engine-temperature coolant. Matrix temperature is controlled by a valve which opens to raise temperature (admit engine coolant) and closes to reduce it (recirculates coolant within the circuit). The coolant flow valve operates on a six (6) second 'duty cycle', during which it may be open for whatever period the control system dictates. FACE vent air temperature however is controlled by the 'cool air by-pass damper' which allows incoming air to flow around the top of the the heater matrix and thus remain unheated.

Because the engine coolant pump is driven proportionally to engine speed, the coolant delivery rate changes with engine revolutions thus causing temperature variations. To stabilize the flow through the matrix, and thus the temperature, an electrically driven circulation pump has been introduced into the system.

Coolant Temperature Signal

This input is required to provide blower inhibit control, to avoid cold air being delivered in heating mode when the engine coolant temperature is below 30 °C and provide progressive blower increase up to 60 °C. The signal is also used to switch the coolant pump off at temperatures below 30 °C to prevent ice forming in the coolant The input also monitors the temperature of the coolant delivered to the heater matrix to assist outlet temperature control.