Service And Diagnosis Information; Control Unit Diagnosis - Porsche P-80 2005 Manual

911 Carrera (993) Model System
Auxiliary Blower Series Resistor
A series resistor is in the auxiliary blower circuit to reduce
voltage to the blower for first (low) speed. If current flow
to the auxiliary blower is too high, a thermoswitch in the
series resistor will open. First speed will then be inopera-
tive and the blower will run at second (high) speed only.
The thermoswitch can be manually reset after repairs.
Notes:
Page 2.10
Climate Control Systems Diagnosis & Repair

Service and Diagnosis Information

Heating-A/C Control Unit Diagnosis
The Heating-A/C Control Unit is located in the instrument
panel and has the manual passenger's controls.
Passengers can select the desired temperature, blower
speed and air distribution conditions. The system will
maintain the set temperature as conditions change.
The Heating-A/C Control Unit has an electronic processor
which compares the interior air temperature value with the
passenger-selected value. If the two values are different,
the Heating-A/C Unit commands electric servo motors to
move air distribution flaps to increase or decrease the
outlet air temperature.
Other sensor inputs to the Heating-A/C Control Unit include
the refrigerant pressure switch and air distribution flap
position.
Blower Control
Blower speed is controlled using an electronic final stage
w/heat sink. The blower regulator is controlled by a digital
pulse-width modulated signal by the heating and AC
Control Module.