New Features In the Automatic Climate Control
NEW FEATURES IN THE AUTOMATIC CLIMATE CONTROL
as of 09/85
The following data describes only those components that exist in addition to or which differ from those of the familiar automatic climate control.
Control Unit:
The control unit consists of a temperature selector (a), push-button switches (b) with 5 functions and the blower switch (c). The control unit contains an electronic system which performs the following functions:
1. Regulates the in-car temperature
2. Controls the blower controller
3. Controls air recirculation
4. Controls the air flaps
Control unit consists of:
a Temperature selector
b Push-button switches with 5 functions
c Blower switch
S24 Fresh/recirculated air switch
Blower Controller:
The blower controller is a transistor controlled constant-current controller. It consists of a cooling unit and an electronics section. The blower controller infinitely regulates the blower motor. It switches off the blower motor in the event of a short circuit or overheating.
The outputs of the control units are designed to be short-circuit-proof. This serves to protect the conductors in the control unit should a short circuit occur.
In the event of a short circuit, the control unit switches off the relevant output, and switches it back on again immediately when the short circuit no longer exists.
The blower controller is located in the blower housing beside the blower motor. In this way, the blower controller is continuously cooled when the blower motor is running.
N29 Blower controller
Function of Blower Control:
The blower controller provides infinitely variable control of the speed of the blower.
The blower controller is connected to the main fusebox and to ground, and is supplied with battery voltage when the ignition is switched on. The blower controller is also connected with the control unit of the automatic climate control by way of a control cable.
Depending on the function selected with the blower switch, the control unit provides a continual control voltage of between 0.4 and 9 volts for the blower controller. The blower controller provides the blower motor with a continual current of between 2.0 and 26 amps, and thus regulates the speed of the blower.
Control Panel:
Control voltages during various functions of the blower switch:
Fixed minimum (9 in control panel)
- approx. 1.0 volts (blower current 5 amps)
Automatic stage (8 in control panel)
- 1.4 to 4.5 volts (blower current 7.5 to 22 amps)
Fixed maximum (7 in control panel)
- 6.0 to 9.0 volts (blower current 28 amps)
In all functions, the control voltages are influenced by the speed of the vehicle provided by the Hall-effect sensor at the speedometer. The control voltage is reduced continually by max. 0.6 volts up to a speed of 200 km/h.
This somewhat reduces the increase in air volume caused by the ram pressure.
When the blower switch is at Automatic, the control voltages are additionally influenced:
- By the nominal and actual in-car temperatures (via in-car temperature sensor and temperature selector)
- By the outside temperature (via the outside air temperature sensor B 10/5 in the air intake)
- By the operating mode of the system (heating or cooling)
- By the coolant temperature (from the coolant temperature sensor)
B 10/5 Outside air temperature sensor
Blower control in function selections (4 in control panel) or (5 in control panel) and (8 in control panel):
a) At coolant temperatures below 40 °C, the blower does not start up if the outside temperature is below 20 °C and the in-car temperature is lower than that set on the temperature selector (cold engine lock).
From a coolant temperature of 40 °C to 80 °C, the control voltage is continually increased from 1.6 volts if (3 in control panel) is selected or 2.0 volts at (4 in control panel) up to a maximum of 4.5 V. This produces an increase in the speed of the blower.
b) At coolant temperatures below 40 °C, the blower starts up immediately if the outside temperature is above 20 °C or the in-car temperature is higher than that set on the temperature selector.
The control voltage of the blower controller is dependent on the in-car or outside temperature (up to max. 4.5 volts).
Blower control in function selections (3 in control panel) or (7 in control panel) or (9 in control panel):
The blower starts up immediately at coolant temperatures below 40 °C. The blower continues to run when the system is switched to (4 in control panel) or (5 in control panel) or (8 in control panel) and can only be switched off using the (6 in control panel) key.
Blower control in function selection (2 in control panel):
The blower starts up immediately at coolant temperatures below 40 °C and is similarly increased relative to the coolant temperature, but not as far as the maximum blower output. The control voltage lies between 1.4 and 5 volts. If the fixed maximum (7 in control panel) on the blower switch is pressed as well, the blower runs at maximum speed regardless of the coolant temperature (blower current 28 amps).
Control of air flaps:
The control of the air flaps is influenced by the temperature sensor for the heat exchanger (B 10/1).
The modes are changed by switching the air flaps at the transition from heating to cooling and from cooling to heating. Several air flaps open and the transition becomes less noticeable. The air flaps are controlled as described in the table overleaf.
B 10/1 Heat exchanger temperature sensor
Y7 Switchover valve Unit (7 Connections)
Control of fresh air/recirculated air flap:
The fresh air/recirculated air flap is controlled:
- Manually via the fresh/recirculated air switch (S 24, 100% recirculated air)
- Automatically by the control unit of the automatic climate control (N 22, 80% or 100% recirculated air)
Function of air recirculation:
Manual air recirculation (100 % in event of unpleasant odors).
If function (3 in control panel) or (4 in control panel) is selected at outside temperatures above 7 °C, and provided the refrigerant compressor still cuts in, the recirculated air flap switches back to fresh air or Automatic 30 minutes after the recirculated air switch is pressed. If the outside temperature is below 7 °C and the compressor no longer cuts in, or if the function (5 in control panel) is selected, it switches back to fresh air or Automatic after just 5 minutes.
This process is repeated when the recirculated air switch is pressed again.
If the recirculated air switch or the ignition is switched off or the function (2 in control panel) is selected, the recirculated air flap moves to the fresh air position.
Automatic recirculation (to improve cooling capacity):
Automatic air recirculation is dependent on the in-car temperature (in-car temperature sensor) and on the difference between the temperature set on the temperature selector and the outside temperature (outside air temperature sensor).
In other words, the higher the in-car temperature or the greater the temperature difference, the earlier the system will switch to air recirculation.
Example a:
With an in-car temperature of approx. 25 °C and a temperature difference (between the temperature set on the temperature selector and the outside air temperature) of more than 8 °C, the system switches to 80 % recirculated air. If the temperature difference increases to above 23 °C, i.e. the outside temperature increases, the system switches to 100 % recirculated air.
If the temperature difference becomes smaller, i.e. the outside temperature drops to below 17 °C, the system switches from 100 % to 80 % recirculated air. If the temperature difference continues to fall to below 5 °C, the system switches back to fresh air.
Example b:
If the temperature difference is 0 °C and the in-car temperature increases to above 50 °C due to the effects of sunlight, the system switches to 80 % recirculated air and then to 100 % recirculated air if the in-car temperature rises above 60 °C.
If the in-car temperature drops to below 50 °C, the system switches to 80% recirculated air and then to fresh air at below 40 °C.
Note:
1. Operation with 100% recirculated air is limited to 30 minutes. The system then switches to 80% recirculated air regardless of the temperature difference.
2. The system can be manually switched to 100% recirculated air for an unlimited period by engaging the temperature selector at "MIN" at outside temperatures above 20 °C.
Control of the diverter flap:
The function of the diverter flap depends on:
- The ratio of the temperature set on the temperature selector to the in-car temperature
- The outside air temperature
The higher the outside temperature, the earlier the diverter flap cuts in, regardless of whether or not the system is operating with recirculated air.
Arrangement of vacuum elements and switchover valve unit for controlling the air flaps:
The switchover valve unit (Y7) consists of 7 individual switchover valves.
It is not possible to repair the switch over valve unit; it must be replaced complete.
B 10/1 Heat exchanger temperature sensor
Y 7 Switchover valve Unit (7 connections
39 Vacuum element for footwell flaps (flaps closed without vacuum)
Air conditioner temperature sensor:
The air conditioner temperature sensor is located in the air stream over the evaporator. Its resistance is relative to the temperature at the evaporator, and the sensor sends this value to the control unit. This temperature sensor causes the compressor to switch off and on more frequently during cooling operation. In this way, the outlet temperature at the nozzles displays only slight variations. It also prevents the evaporator icing up.
B10/6 Evaporator temperature sensor
Emergency cutout of refrigerant compressor:
To prevent any thermal overload of the motors, an emergency cutout facility has been integrated into the control unit of the automatic climate control. This is controlled by the coolant temperature gauge sensor (B 13 or B 11/7) via the control unit of the automatic climate control.
Arrangement of coolant temperature gauge sensor (B 13), engine 103
Function of emergency cutout:
If the coolant reaches a temperature of above 117 °C, the cut-in duration of the refrigerant compressor is reduced by 50 % and the compressor is switched off completely at temperatures above 120 °C.
If the coolant temperature drops below 117 °C, the cut-in duration remains at 50% until it drops below 114 °C when the refrigerant compressor cuts back in again fully.
Note: If the refrigerant compressor fails to cut in, the coolant temperature gauge sensor (B 13 or B 11/7) may be faulty or the cable from the control unit to the temperature sensor (B 13 or B 11/7) may have an open circuit (refer to wiring diagram).