4. Cab heating and ventilation system
The electric circuitry of the system has the following peculiarities:
The winding of the heater interlock relay K3 serving for preventing the discharge of
the storage battery when switching on the heater with the engine not running is
connected between the terminal “Д” of the alternator (G1) (wire Р) and the tractor
body (wire Г);
To provide for reduced rotational speed of the fan in case of installation of the motor
with the power of 90 W (М1), the power supply circuit comprises an additional
resistor (R1). The increased rotational speed is provided by the respective position
of the switch (SA4) supplying the fan motor with bypassing the additional resistor.
In case of installation of the motor with the power of 120 W (М7) to the heater unit,
the circuit from the fuse “1” (25А) of the box F3 (wire Кч) to the switch (SA4)
comprises the relays (K10) for setting the minimum rotational speed and (K9) for
setting the maximum speed. The said relays ensure the protection of the contacts of
the switch (SA4) against overcurrent.
When the engine has been started and the voltage at the terminal “Д” of the
alternator has exceeded 8 V, the interlock relay (K3) operates, its contacts “87-30”
become closed and the supplying voltage is applied to the switch (SA4) (wire С3)
(contact “L”).
The switch (SA4) applies the supply voltage to the motor and provides the necessary
rotational speed of the fan.
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