Ch 6 page 24 ELECTRICAL SYSTEM Flap motor The flap motor is a reversal polarity electric motor. This is used to close the HVAC unit from the outside air when the recirculation button is pressed on the control panel. It is a two wire motor that uses two external switches and parallel diodes to limit the movement in both directions. When the flap is in one of the end positions, one switch will be open and the diode will make sure that only movement in the opposite direction is possible. Applying 24 V between pin B8 to pin B17 of the connector on the control panel will move the flap to the open position. Applying 24 V between B17 to pin 8 will put the flap into the recirculation position.
Figure 32 Temperature sensors There are three sensors used inside /around the HVAC unit. They are used to measure the temperature inside and outside the unit. Also one measures the mixed air temperature. These are NTC resistors. Measured resistance is 13K Ohm at around 18 °C (64 °F). At 9 °C it is around 21k Ohm. Figure 33 Evaporator temperature sensor This is a PT1000 sensor which is installed into the evaporator. The resistance is around 1000 Ohm at 0 °C. Figure 34 Pressure sensors These sensors are used to measure the pressure in both high and low pressure parts of the A/C system. The pressures are used by the VCU to determine if the compressor is allowed to run.
These two sensors are mounted on the outside of the HVAC unit. They have a current output between 4 and 20 mA that corresponds to 0 - 30 bar (425 psi). Figure 35 SHOP MANUAL