Porsche P-80 2005, Manual

Page: 61 / 108

Cayenne Model System
Climate Control Systems Diagnosis & Repair
Page 4.3
Cayenne A/C System Description
The Cayenne V6 has a heating system in conjunction with
manual air conditioning for climate control of the
passenger compartment, satisfying the highest demands
in comfort. Air conditioning with 2-zone or 4-zone control,
is available as a option.
The Cayenne S and Cayenne Turbo have 2-zone air condi-
tioning as standard equipment, with 4-zone being available
as a option.
Compressor, Cayenne (V6)
On the manual air conditioning, the air blending swash-
plate (adjustable) compressor, similar to the 2-zone air
conditioning, is used. The swash plate is adjusted through
an electronic control valve integrated in the compressor.
The control valve is actuated by a variable PWM signal
from the air conditioning control unit (control panel). The
variation of the PWM signal is basically caused by the
vaporizer temperature sensor. As the compressor works
with a variable delivery rate and zero delivery (delivery rate
dd5%) is theoretically possible, it is not necessary to
control the air conditioning cooling output through the
switching on and off of a compressor relay (the
compressor always runs if the engine is running).
1 - Plug connector (electronic control valve)
2 - Pressure relief valve
3 - Connector opening, low pressure side
4 - Electronic control valve
Compressor, 2-Zone & 4-Zone
The Cayenne is equipped with a swash plate (regulated)
compressor controlled on the low side that is similar in
function and design to a compressor in a sports car. The
refrigerant has a pressure of 145-435 psi (10-30 bar) after
exiting the compressor and a temperature of about 212°
F. (100° C). The compressor runs whenever there are RPMs.
Through an electronic control valve, integrated into the
compressor, the intake pressure (low pressure side, about
14.5-43.5 psi/1-3 bar) in the compressor housing has an
effect on the swash plate. The control valve is triggered by
a PWM signal from the control module of the climate
control. The basis for the triggering of the control valve is
taken from the signal of the evaporator temperature
sensor. The basis frequency for the valve is 400 Hz.
The piston stroke can be continuously varied, a large
stroke for large refrigerant capacity and a smaller stroke
for smaller capacity. Because the compressor works with
a variable capacity demand, there is no compressor relay.
This means that the compressor is always turning but
there is no output at the lowest portion of the compressor
stroke.