2. Start the engine.
3. Move the lower lever of the heater control unit to the extreme left position (blue sector).
4. Using the heater fan control handle, alternately turn on the three speeds of the electric fan. Based on the intensity of the air flow from the ventilation grilles, check the operation of the electric fan and the change in its rotation speed when changing modes (1 - minimum speed; 2 - average speed; 3 - maximum speed). If the electric fan does not work in all modes, then check the additional resistor (see "Additional resistor - removal, testing and installation") and a switch. If the electric fan does not turn on at all, then check the electric fan power supply circuit (see "Electrical equipment - technical condition check").
5. Turn on the maximum speed of the electric fan.
6. By moving the left upper lever of the heater control unit, we monitor the change in the direction of the air flow from the central ventilation grilles to the driver and passenger footwell. If the flow distribution does not change, then the air duct flap drive is most likely faulty.
7. By moving the right upper lever of the control unit, we check the change in the intensity of the windshield and front door glass blowing. If the intensity of the glass blowing does not change, then, most likely, the air duct flap drive is faulty.
8. After warming up the engine to operating temperature, move the lower lever of the heater control unit to the red sector.
9. Make sure that the temperature of the air coming out of the ventilation grilles begins to rise. If the temperature does not rise, then the central damper drive or the heater tap may be faulty, or the heater radiator may be clogged.
10. After the temperature of the air coming out of the heater reaches its maximum, move the lever to the blue sector - the temperature of the supplied air should quickly decrease. If the temperature does not decrease, either the heater valve or the central flap drive is faulty.
11. Under the dashboard on the passenger side, visually check for coolant leaks from the heater radiator tap. Replace the faulty tap (see below, "Heater tap - removal and installation").