Vehicle heater control unit. Encyclopedia of radio electronics and electrical engineering

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All VAZ cars of the tenth family are equipped with a passenger compartment heater equipped with an automatic control unit. Practice shows that several years of using the machine is enough to identify the shortcomings of the existing heating system. The author of this article tells how to eliminate them.

During the operation of my VAZ-2111 car, I had to constantly encounter problems with controlling the interior heater. So, for example, when the roof of the car is heated under the influence of direct sunlight, the temperature sensor operating in the control unit and located in the headliner heats up earlier than the car interior. As a result, the heater switches to interior cooling long before the completion of its heating. When driving for a long time on the highway in cool weather, the driver's right leg begins to freeze due to the full opening of the heater damper. The fact is that the heater control unit always works in automatic mode, with the exception of the extreme positions of the control, when either hot air or cold air is supplied. In this case, the heater damper, when the temperature set by the switch is reached, moves automatically by approximately 50% of the working stroke. Therefore, the air entering the cabin from the heater changes abruptly from cold to hot and vice versa, i.e., it practically never becomes warm.

Fig. 1

If we add to this that the reliability of the control unit leaves much to be desired - after three years of operation it often fails - it becomes clear why I decided to develop a home-made heater control device. It is electronic-mechanical and works similarly to the cable drive of the heater damper of a VAZ-2108 car. The cable drive implements proportional control of the damper, that is, as far as the position of the regulator in the cabin has changed, it will move as much.

The diagram of the control unit is shown in fig. 1. The basis of the device is a control voltage divider, one arm of which is a set of resistors R1-R8, switched by the heater damper position switch SA1, and the other is a variable resistor R9 mounted on the motor gearbox M1, which moves the damper. That is, the resistor engine is mechanically connected to the heater damper.

The voltage from the divider through two emitter followers on transistors VT1, VT2 is fed to the input of two comparators assembled on the op-amp DA1.1 and DA1.2. The first responds to an increase in the voltage at the inverting input relative to the voltage at the non-inverting one, and the second - to a decrease in the voltage at the inverting input relative to the voltage at the non-inverting one. The voltage at the non-inverting input of both op-amps is set by resistive dividers R15R16 and R17R18. To ensure the switching voltage hysteresis, the resistance of resistors R16 and R18 differs by 200 ohms. This is required to prevent the occurrence of a self-oscillating mode of movement of the heater damper.

In a balanced state - the damper position remains unchanged - at the output of the op-amp DA1.1 there is a voltage close to 9 V, and at the output of the op-amp DA1.2 - close to zero, powerful transistors VT3-VT6 remain closed.

Fig. 2

When the switch knob SA1 is moved in the direction of increasing the temperature in the cabin (down the circuit), the resistance of the upper arm of the control voltage divider decreases, the voltage at the base, and hence at the emitter of the transistor VT1, becomes greater than at the non-inverting input of the op-amp DA1.1. As a result, the op-amp switches to a state in which its output voltage becomes close to zero, and the inverter DD1.2 - to unity. As a result, the transistor VT4 opens.

At the same time, a low level occurs at the output of the inverter DD1.4, which opens the transistor VT3. The rotor of the electric motor M1 and the shaft of the heater damper drive reducer begin to rotate in the direction of its opening. The gear shaft moves the engine of the resistor R9, reducing the resistance of the lower arm of the control divider. After some time, the voltage at the inverting input of the op-amp DA1.1 will again become less than at the non-inverting one, the comparator will switch to its original state, the transistors VT3 and VT4 will close and the motor will turn off.

When the SA1 switch knob is turned in the direction of lowering the temperature in the cabin (up according to the diagram), the voltage at the inverting input of the DA1.2 op-amp will become less than that set at the non-inverting one, the op-amp will switch to a high voltage output state. It is easy to see that transistors VT5 and VT6 will open and the rotor of the electric motor will begin to rotate in the opposite direction - the damper will close.

Fig. 3

After some time, the ratio of voltage values ​​at the inputs of the op-amp DA1.2 will be restored, the op-amp will switch to its original state, the transistors VT5, VT6 will close - the motor will turn off. Diodes VD1 and VD2, resistor R23 and LED HL1 serve to indicate the movement of the heater damper. While the motor rotor is rotating, the LED is on.

The device is assembled on a printed circuit board made of foil fiberglass with a thickness of 1,5 mm. The board drawing is shown in fig. 2. It is installed in the heater controller housing, above the main board. The numbering of contacts of connectors X1 and X2 in the diagram of fig. 1 corresponds to the pin numbers of the "VAZ" connectors soldered into the main board. The main board is left in its place so as not to change the switching of the switch SA1 of the heater control unit and use the already installed connectors.

The numbering of connector pins is shown in fig. 3 (mostly those that appear in the diagram in Fig. 1 are marked). To help identify the pins, the corresponding wire colors are shown below. For connector X1: 1 - green; 2 - pink; 3 - green with a black stripe; 4 - blue with a pink stripe; 5 - green with a red stripe; 8 - brown. For connector X2: 3 - black (common wire); 6 - blue (positive power wire). Unfortunately, the color marking of wires cannot be considered strict - there have been cases of color deviation from the specified one.

Before mounting the board of the regulator block into the housing on the main board, the printed conductors leading to terminals 1, 2, 4, 8 of the X1 connector must be cut. The current consumed by the electric motor of the gearbox (using the existing drive from the VAZ-2110) does not exceed 100 mA, so neither the voltage regulator DA2 nor the output transistors require heat sinks.

The device uses fixed resistors MLT-0,125, the oxide capacitor C4 is imported, the rest are ceramic KM-5. Transistors and diodes can be used with any letter index. Instead of the OU K140UD20, its analogue UA747 is suitable (with the appropriate correction of the printed circuit board); you can also use two op-amps K140UD6 or K140UD7, but in this case, serious changes will have to be made to the board. The K561LN2 chip is replaceable by its analog CD4049, and KR142EN8A - 7809.

It should also be borne in mind that the new units (2005 release) have ceramic switches with sputtered upper-side resistors of the control divider. In this case, the resistor R10 must be replaced with another one, with a resistance of 470 ohms. Instead of switch SA1, you can install a variable resistor with a resistance of 3,3 kOhm with a linear characteristic (A) for smooth damper control.

Author: I. Kuzenkov, Apatity, Murmansk region; Publication: radioradar.net

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