Heater Control Valve: Description and Operation

Duovalve

The duovalve regulates the quantity of coolant flowing through the heater core.

When the temperature dial is set to "MIN" the push-button control module switches the duovalve solenoid (Y21) to ground, the solenoid pulls in and blocks the coolant flow through the heater core separately on the left and right sides.
If the temperature dial is set to "MAX" the push-button control module interrupts the ground connection, current does not flow through the solenoid and the maximum quantity of coolant flows through the heater core.

In normal operation the push-button control module switches the ground connection intermittently.
The locking and closing times of the duovalve (Y1) are subject to deviations between the actual temperature and set temperature.

Residual engine heat utilization
In the residual engine heat utilization mode the interior temperature is controlled in the same manner as while driving; the coolant is circulated by the coolant circulation pump (M13).