Porsche P-80 2005, Manual

Page: 49 / 108

Sports Cars System
Climate Control Systems Diagnosis & Repair
Page 3.15
Sensors
Refrigerant pressure is monitored to prevent A/C system
operation when pressures are very low or high. High refrig-
erant pressure also signals increased condenser fan
speed for additional airflow and cooling.
3-Way Refrigerant Pressure Switch (High/Low and
Medium Pressure Switch) – Sports Cars Up To M.Y. 2004
The 3-way refrigerant pressure switch (high/low and
medium pressure switch) has two switches in one unit.
The first switch is a high/low pressure switch in the
compressor clutch circuit. The switch is normally closed,
and the contacts will open when refrigerant pressure
exceeds very high or low thresholds. As long as
refrigerant pressure is typically between 2-26 bar (29-377
psi), the switch contacts will remain closed. When the
high/low pressure switch contacts open, this opens the
power circuit to the A/C compressor relay. The switch
contacts will again close when pressures are typically
between 2.6-20 bar (38-290 psi).
The second switch is the medium pressure switch. This is
a normally-open switch, and the switch contacts will close
when refrigerant pressure typically exceeds 16 bar (232
psi). The medium pressure switch is in the DME circuit to
control the condenser fan. The DME control unit runs the
condenser fan at second speed when the switch contacts
close. This high fan speed moves more air through the
condenser and reduces high side refrigerant pressure. The
3-way pressure switch is installed in the system high side
near the expansion valve.
Pressure Sensor – Sports Cars M.Y. 2005 - on
The pressure sensor is an essential instrument in
assessing the air conditioning system. It detects the
current pressure in the system and supplies a PWM signal
(
PulseWidthModulation) to the a/c control unit. The A/C
Control Unit relays this signal to the CAN bus for further
use.
This PWM signal is employed for the purposes of:
• Low-pressure shut-down (p < 29 psi/2 bar)
• High-pressure shut-down (p > 406 psi/28 bar)
• Condenser cooling (see also section “Condenser fan”)
The following components serve as actuators:
• Drive motor for temperature mix flap
• Drive motor for central distributor flap
• Drive motor for defrost/footwell distributor flap
• Drive motor for fresh air/recirc. air distributor flap
• PWM - fan motor voltage
The pressure sensor is installed in the system high side
near the expansion valve.
1 - Expansion valve
2 - Service connection suction side
3 - Service connection pressure side
4 - Air conditioning system pressure sensor (located on the high-
pressure side of the cooling circuit)