Porsche P-80 2005 User manual

AfterSales Training
Climate Control Systems Diagnosis & Repair P-80
®

Porsche AfterSales Training
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Important Notice:The contents of this AfterSales Training brochure was originally written by Porsche AG for its rest-of-world
English speaking market. The electronic text and graphic files were then imported by Porsche Cars N.A, Inc. and edited for con-
tent. Some equipment and technical data listed in this publication may not be applicable for our market. Specifications aresub-
ject to change without notice.
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make changes without notice.
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without written authorization from publisher. AfterSales Training Publications
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the Porsche Crest®, Porsche®, Boxster®, Carrera®, Cayenne®, Tiptronic®, VarioCam®, PCM®, 911®, 4S®, and the model
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Part Number - PNA P80 001 Edition - 11/05
Electrical Troubleshooting Logic
1 - Do you understand how the electrical consumer is expected to operate?
2-Do you have the correct wiring diagram?
3 - If the circuit contains a fuse, is the fuse okay & of the correct amperage?
4 - Is therepower provided to the circuit? Is the power source the correct voltage?
5 - Is the ground(s) for the circuit connected? Is the connection tight & free of resistance?
6 - Is the circuit being correctly activated by a switch, relay,sensor,microswitch, etc.?
7-Are all electrical plugs connected securely with no tension, corrosion, or loose wires?

Table of Contents
Climate Control Systems Diagnosis & Repair
Chapter Description Section
Introduction ..............................................................i
Air Conditioning Basics .....................................................1
911 Carrera (993) 1995 - 98 ................................................2
Sports Cars, 911 Carrera (996)/(997) & Boxster (986)/(987) ......................3
Cayenne (9PA) 2003 - 0n ..................................................4
A/C Refrigerant System Service and Diagnosis .................................5
BUS Communications ......................................................6
Conversion Charts ........................................................7

Climate Control Systems Diagnosis & Repair

Introduction
Climate Control Systems Diagnosis & Repair Page i
In the past, air conditioning in automobiles was considered an option and a luxury. A/C was rarely found
in high performance vehicles and the customer was willing to trade comfort for performance.
The rules have changed and today’s customer expects A/C to be an included feature. High levels of
performance and comfort are expected. All current Porsche models sold in North America have A/C
standard, and all US models are equipped with automatic climate control systems.
With the push of a button, today’s customer expects rapid heating and cooling. Only when the system
fails to function will the customer be consciously aware of it. This is where you, the technician, come in.
In order to satisfy the Porsche customer’s high expectations, you will need to successfully diagnose,
test and repair climate control systems in a timely manner.
After a climate control system repair, the first thing that the customer will do is operate the system.
Success or failure is measured in degrees.

Page ii Climate Control Systems Diagnosis & Repair
Introduction
Ozone Depletion and Global Warming
The Ozone layer is in the stratosphere 16-48 kilometers
(10-30 miles) above the Earth's surface. This layer shields
the earth from much of the sun's ultraviolet radiation.
Chlorine found in R-12 refrigerant released into the atmos-
phere can seriously damage the Ozone layer.
Energy from the sun drives the earth's weather and
climate. Sunlight heats the earth's surface, and some of
the sunlight is reflected in the form of infrared radiation.
Much of this radiant energy dissipates into space, but
some is reflected back into the atmosphere. Atmospheric
greenhouse gases (water vapor, Carbon Dioxide, and
other gases) trap some of the outgoing energy, retaining
heat (like the glass panels of a greenhouse). The trapping
of too much radiant heat energy is suspected to cause
Global Warming.
There is strong evidence that the quantity of Carbon
Dioxide in the atmosphereand the rising average world
temperatures are related. Carbon Dioxide, one of the
gases emitted by internal combustion engines, has a
significant greenhouse effect, but R-12 refrigerant in the
upper atmosphere has a Global Warming Potential (GWP)
8,500 times greater than Carbon Dioxide. R-134a
refrigerant is better, but still has a GWP value of 1,300.
The discovery of these problems caused the governments
of the industrialized world to establish a time table for the
reduction and eventual elimination of the production of
chemicals that deplete the Ozone layer. The Montreal
Protocol was enacted in September 1987, and laws were
enacted requiring the automotive service industry to
modify the servicing of A/C refrigerant systems.
All refrigerants used in automotive air conditioners must
now be recovered and recycled whenever an A/C system
is opened for service or repair. Also, refrigerant R-12
(FREON) is no longer produced, and has been replaced
with a less harmful refrigerant, R-134a (SUVA). R-134a is
the only alternative refrigerant for R-12 that is approved
for use in new automobiles by all auto manufacturers.
Porsche phased-in the use of R-134a in 1993. Refer to
page I-21 for more refrigerant information.
Any person servicing motor vehicle air conditioning
systems MUST by law be properly trained, certified and
use approved refrigerant recycling equipment. Technicians
must successfully complete an EPA approved recycling
course and be tested. Certification is available from the
National Institute for Automotive Service Excellence (ASE)
and the Mobile Air Conditioning Society (MACS). State and
local jurisdictions may have their own certification require-
ments that supersede federal requirements.

Air Conditioning Basics
Climate Control Systems Diagnosis & Repair Page 1.1
Subject Page
Air Conditioning Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..1.3
Principles of Heat Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.3
The Refrigeration Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.7
Compressor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.8
Pressure Relief Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.10
Condenser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.11
Receiver/Dryer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.11
Evaporator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.12
Thermostatic Expansion Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.13
Lines and Hoses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.14
Service Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.14
Refrigerants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.15

Page 1.2Climate Control Systems Diagnosis & Repair
Air Conditioning Basics
Notes:

Air Conditioning Basics
Climate Control Systems Diagnosis & Repair Page 1.3
Air Conditioning Overview
Air conditioning is the process of moving heat energy from
one place in the vehicle to another. Doing this raises or
lowers the temperature of the air in the vehicle interior.
The A/C system is a closed loop system in which a refrig-
erant is pumped by the compressor through the circuit
continuously. While it is being pumped, the refrigerant
changes state from liquid to gas and back again. The
refrigerant changes from liquid to gas in the evaporator as
it removes heat from the passenger compartment. Then
the refrigerant gas condenses back to liquid in the
condenser, giving off heat to ambient (outside) air. This is
ashort description of how A/C works. These concepts will
be discussed in more detail in the next section.
Principles of Heat Transfer
There are four principles of heat and heat transfer that
apply to automotive heating, air conditioning and climate
control systems:
1. Heat always flows from hot to cold.
2. Materials absorb or give off large amounts of heat
when changing state.
3. The pressure of a liquid or gas varies with its tempera-
ture and the temperature of a liquid or gas varies with
its pressure.
4. The boiling point of a liquid varies with its pressure.

Page 1.4Climate Control Systems Diagnosis & Repair
Air Conditioning Basics
1. Heat always flows from hot to cold.
Heat is a form of energy. Cold is a term that means less
heat is present. Cold materials contain less heat energy
than hot materials and heat always flows from the hotter
material to the colder.
For example, if you hold an ice cube, your hand will feel
cold. The ice removes heat from your hand and you sense
the loss of heat. If you touch something warm, you feel the
heat flowing into your hand. If a large amount of heat
transfers, you may be burned and feel pain.
Practical Application
•Heat energy contained in the passenger compartment
air is absorbed by the cold refrigerant in the A/C evapo-
rator.
•Hot refrigerant gives offheat and is cooled by cooler
ambient air flowing through the A/C condenser.
In both cases, heat moves from hotter to cooler.
Notes:
2. Materials absorb or give off large amounts of
heat when changing state.
Sweating makes us feel cooler. As liquid water on our skin
evaporates, it removes body heat. In a similar way, refrig-
erant vaporizing (changing from liquid to gas) inside the
A/C evaporator absorbs heat from the warmer air around
the evaporator.
Practical Application
•In the evaporator, liquid refrigerant boils at
temperatures below the temperature of the air in the
passenger compartment. The refrigerant absorbs large
quantities of heat, far more heat than it would if it
remained a liquid.
•In the condenser,the reverse takes place. Here, hot
refrigerant gas condenses back to liquid and gives off
large amounts of heat to the cooler atmosphere. The
refrigerant gives up far moreheat than it would if it
remained a gas.
To explain, we need to look at two kinds of heat energy:
Sensible Heat and Latent Heat.
Sensible Heat – is measurable heat - a measurable
change in the temperatureof a material. Adding heat
energy raises the measurable temperatureof a material
and increases Sensible Heat. If we heat a pot of water on
astove, the temperature of the water will increase and we
can measure this change with a thermometer (see illustra-
tion, below).
Latent Heat – is heat energy that is added to a material
Sensible Heat
Heat energy
increases
temperature
of liquid
No change
of state

Air Conditioning Basics
Climate Control Systems Diagnosis & Repair Page 1.5
causing it to change state. The temperature of the
material remains the same during the change of state. We
can raise the temperature a pot of water to the boiling
point (100° C/212° F) by adding Sensible Heat energy, but
tomake the water boil and change state from liquid to
gas, it takes much more heat energy in the form of Latent
Heat. Similarly, when a gas condenses to a liquid, large
amounts of Latent Heat energy are released (see illustra-
tion, below).
The unit of heat energy is the BTU (British Thermal Unit).
One BTU = the amount of heat energy required to raise
the temperature of one pound of water one degree F. At
sea level pressure, water boils at 212° F. In order to raise
the temperature of one pound of water from 211° F to
212° F, only one BTU heat energy is needed. But to
change that same pound of water at 212° F to one pound
of steam (gas) at 212° F requires 970 BTUs, a much
greater quantity of heat. When the water condenses back
to a liquid, it gives off the same 970 BTUs of heat.
In the A/C system, refrigerant evaporates and condenses
over and over as it is pumped through the system. R-134a
refrigerant absorbs or gives offlarge amounts of latent
heat energy (about 85 BTU/lb) as it changes state. This is
the key to the efficiency of A/C systems.
3.The pressure of a liquid or gas varies with its
temperature and the temperature of a liquid or
gas varies with its pressure.
The pressure of the refrigerant in the closed A/C circuit
will vary with changes in temperature, and the temperature
of the refrigerant varies with changes in its pressure. With
A/C off and at an ambient temperature of 21° C (70° F),
the pressure in a fully charged system will be
approximately 4.8 bar (70 psi).
As the temperature rises, the pressure will also rise. The
table below shows the temperature/pressure relationship
for R-134a at temperatures between -30° C (-22° F) and
70° C (158° F).
At -30° C (-22° F) refrigerant pressure drops to 0 bar (0
psi). At this temperature, liquid refrigerant in an open
container will not boil and will remain a liquid.
Practical Application
•The job of the A/C compressor is to compress
refrigerant gas, raising its pressureand temperature
and concentrating the heat. The refrigerant flows to the
condenser where it is much hotter than the ambient air
blowing through and gives up latent heat to the air.
•In the evaporator, refrigerant is exposed to low
pressure. This lowers its temperature and the cold
refrigerant absorbs latent heat from the passenger
compartment.
Note:
The temperatures of the A/C lines when the A/C is ON.
The high pressure lines will be warm or hot, the low
pressure lines will be cool or cold.
R-134a Refrigerant Pressure vs. Temperature
R-134a Refrigerant pressure vs. temperature
Temperature ° F
-22
0.0
-4
4.4
14
14.5
32
27.5
50
45.0
86
97.2
104
132.0
122
177.0
140
229.2
158
293.0
68
68.2
Pressure (psi)
Latent Heat
Heat energy
changes liquid
to vapor (gas)
Temperature of
liquid does not
change
Change of
state occurs

Page 1.6Climate Control Systems Diagnosis & Repair
Air Conditioning Basics
4. The boiling point of a liquid varies with its
pressure.
The boiling point of a liquid changes with pressure. For
example, engine coolant temperatures can easily climb
above the boiling point of the coolant/water mixture at sea
level pressure, about 108° C (226° F). By increasing the
pressure to 1 bar (15 psi) the boiling point is raised to
128° C (263° F).
Practical Application
•When the A/C system is operating, the refrigerant
pressure in the evaporator is low which lowers its
boiling point. This allows the liquid refrigerant to boil
and to change state to a gas, absorbing latent heat.
•In the condenser,the pressure of the refrigerant gas is
high, raising the boiling point and allowing it to
condense to liquid as heat is removed.
R-134a refrigerant is as a gas at atmospheric pressures
and ambient temperatures. In the closed refrigerant
circuit, some refrigerant is in liquid form because of the
higher pressure. As with water, the boiling point of refrig-
erant increases as its pressureincreases.
Reducing pressure to below-atmospheric (partial vacuum)
lowers the boiling point of a liquid. The table shows the
boiling point of water at several low pressures. The value
29.92 in. Hg is atmospheric pressure at sea level. At this
pressure, the boiling point of water is 100° C (212° F). At
higher altitudes, such as in Denver, the pressure is lower,
and therefore the boiling point is lower. This is why baking
or cooking times are longer at high altitudes.
On the table, note the low pressure at which water will boil
atroom temperature (shown in bold). This low pressure is
attained during refrigerant system evacuation. At this low
pressure, any water present in the A/C system will boil off.
Notes:

Air Conditioning Basics
Climate Control Systems Diagnosis & Repair Page 1.7
The Refrigeration Cycle
As we have said, air conditioning is the process of moving
heat energy from one place in the vehicle to another. The
A/C system is a closed system in which the compressor
pumps the refrigerant through the circuit over and over
whenever the A/C is ON.
While it is being pumped, the refrigerant changes state
from liquid to gas and back again. The refrigerant changes
from liquid to gas in the evaporator as it removes heat
from the passenger compartment. Then the refrigerant
gas condenses back to liquid in the condenser, giving up
heat to ambient (outside) air. The refrigerant does not get
worn out or used up unless there is a mechanical problem
or a leak.
The amount of heat moved from inside to outside the
vehicle determines the heat load. Both temperature and
humidity affect the heat load. The refrigerant circulates in
the closed circuit made up of these components:
•Compressor
•Condenser
•Receiver/Dryer
•Thermostatic Expansion Valve
•Evaporator
•Lines and Hoses
•Refrigerant
•Regulation and Control Devices
High and Low PressureSections
The system is divided into high pressure and low pressure
sections. They arethe "high side" or discharge (D), and
"low side" or Suction (S). The compressor is the pump that
raises refrigerant pressure on the high side of the system
and reduces pressure on the low side.
•The compressor and the expansion valve separate the
two sides of the system.
•The condenser and receiver dryer are always on the
system high side.
•The evaporator is always on the system low side.
Notes:

Page 1.8Climate Control Systems Diagnosis & Repair
Air Conditioning Basics
Compressor
The compressor is an engine-driven refrigerant pump. It
compresses the refrigerant gas to raise both temperature
and pressure. The compressor also moves refrigerant
through the system.
All Porsche Sports Cars and Cayenne A/C compressors
are variable displacement swash plate designs. Fixed
displacement compressors were used on 911 Carrera
(993) and earlier models.
The compressor is belt driven. On Sports Cars an electro-
magnetic clutch is built into the compressor pulley to
engage and disengage the drive. On Cayenne, there is no
clutch. The compressor shaft turns at all times with the
engine. When no A/C is desired, compressor displacement
can be reduced to nearly 0%.
Compressor piston downstroke draws in low pressure
refrigerant gas from the evaporator.On the upstroke, the
refrigerant is compressed, raising both pressure and
temperature. Refrigerant pressure increases from approx.
0.6-1.7 bar (9-25 psi) to approx. 6-25 bar (87-363 psi).
The compressed refrigerant gas is pushed out of the
compressor to the condenser. The compressor can raise
the pressure of the refrigerant because it is pumping
against a restriction created by the expansion valve. The
system high side contains high pressure refrigerant, and
includes the compressor outlet, condenser, receiver-dryer
and expansion valve inlet. The flow of refrigerant gas into
and out of the compressor is controlled by reed valves.
Reed valves are flat plates of spring material located in the
cylinder head above each piston. They bend one way only
and allow flow in one direction. They open and close auto-
matically in response to pressure changes as the pistons
travel up and down.
The reeds aredesigned to pump refrigerant gas only, and
the compressor pistons have little clearance at the top of
their stroke. Liquid refrigerant must be kept out of the
compressor as it can hydraulic lock and damage it.
Fixed Displacement Compressors
Fixed displacement compressors have a fixed piston
stroke and always pump the same volume of refrigerant
for each revolution of the compressor shaft. The piston
stroke never varies and the compressor's displacement
never changes.
All A/C compressors must have sufficient capacity for
good cooling under high heat load conditions and low
engine speeds. Since fixed displacement compressors
cannot vary the amount that they pump, under conditions
with high engine speed and low heat demands, these
compressors have much greater capacity than is required.
Energy can be wasted pumping this excess refrigerant.
Also, the compressor clutch may cycle ON and OFF more
frequently than is desired.
Notes:

Air Conditioning Basics
Climate Control Systems Diagnosis & Repair Page 1.9
Variable Displacement Compressors
Porsche vehicles today use a variable displacement
compressor. Seven axial pistons are arranged
concentrically around the central compressor shaft. A
smooth disk is attached to the compressor shaft. Slipper
shoes follow the disk's oscillating motion and the angle of
the disk transmits reciprocating forces to the pistons.
Variable displacement compressors can vary the piston
stroke and can change output volume. The longer the
piston stroke, the greater the displacement and output.
The stroke is determined by the angle of the swash plate
on the compressor shaft. Variable displacement compres-
sors change the swash plate angle to match the
refrigerant flow rate to the heat load on the system.
Sports Cars – Variable Displacement Compressor,
Low Displacement Position
Sports Cars – Variable Displacement Compressor,
High Displacement Position
Variable displacement compressors are more efficient
than fixed displacement compressors because they pump
only enough refrigerant to achieve the desired cooling.
Energy is not wasted pumping more refrigerant than is
necessary. Also, clutch cycling is eliminated and engine
idling is improved with variable displacement
compressors.
Heat Load
The compressor senses system refrigerant pressures to
determine heat load and automatically adjust the volume
of refrigerant pumped for optimum heat transfer. The
output of the compressor varies between 5% and 100%.
Compressor displacement is 160 cm3at 100% output.
Low Heat Load - 5% Output
The conditions are met when engine r.p.m. is consistently
high, e.g. expressway driving, and/or temperature is low.
The suction pressure is relatively low and the control valve
is open. The angle of the rotating disk is at its lowest and
so delivery is at its minimum.
High Heat Load - 100% Output
The conditions aremet when engine r.p.m. is consistently
low and/or temperatureis high. The suction pressure is
high and closes the control valve. The angle of the rotating
disk is at its greatest and so delivery is at its maximum.
Notes:

Page 1.10 Climate Control Systems Diagnosis & Repair
Air Conditioning Basics
Mechanical Regulating Valve
Porsche Sports Cars use variable displacement compres-
sors with mechanical regulating valves. Cayenne models
have a variable displacement compressor controlled by a
PWM electronic control valve. Both types regulate
compressor displacement by changing pressure in the
crankcase under the pistons.
Pressure Relief Valve
Porsche A/C compressors have a spring loaded mechan-
ical pressure relief valve. If system pressures get danger-
ously high, the valve will open and vent the excess
pressure. The valve closes when pressures have dropped
to safe levels to prevent the complete loss of refrigerant.
Opening pressureis approximately 38 bar (550 psi). The
valve will close when pressures have dropped to approxi-
mately 30-35 bar (435-508 psi). Removal of the pressure
relief valve first requires recovery of the refrigerant from
the system.
Lubrication
All A/C compressors requires oil for lubrication. The oil
reduces internal friction and heat and helps to seal moving
parts. This lubricant is carried by the flow of refrigerant
throughout the system and it must be compatible with the
refrigerant, seals and components.
Porsche A/C systems with R-134a refrigerant use
synthetic PAG (polyalkylene glycol) or ester oil. R-12
systems use mineral oil. These oils are not compatible.
Mineral oil will not mix with R-134a refrigerant and must
not be used in R-134a systems. Since the oil flows with
the refrigerant throughout the system, a portion of the
total oil charge must be replaced when any component is
replaced. Some oil may also be removed along with the
refrigerant when discharging a system.
A/C service stations have provisions for capturing and
measuring any oil removed so that an equal amount can
be restored. A typical system contains approx. 195 cm3
(6.6 oz.) of ND8 PAG oil. Refer to Service Information for
specifications regarding the amount of oil to add for each
system component.
Caution:
•Always store refrigerant oil in closed containers. These
oils are very hygroscopic, that is, they readily absorb
moisture.
•Never reuse refrigerant oil from a system. Always
replace with fresh uncontaminated oil.
•Always consult the Repair Information for the correct oil
specification and quantity.

Air Conditioning Basics
Climate Control Systems Diagnosis & Repair Page 1.11
Condenser
The condenser is a heat exchanger located in the front of
the vehicle. It is similar to the engine radiator and has a
large surface area for efficient heat transfer. Some
Porsche models use two condensers. The condenser is on
the A/C system high side and contains high pressure
refrigerant.
The condenser allows high pressure, hot refrigerant gas to
give offheat energy to cooler air passing through the
condenser fins. Forward motion of the vehicle and electric
fans both promote this air flow.
The refrigerant changes state in the condenser in this
sequence:
•High pressure refrigerant enters the condenser as a hot
gas: 60-100° C (140-212° F).
•The heat energy that was absorbed by the refrigerant in
the evaporator is transferred to the cooler ambient air
passing over the condenser's tubes and fins.
•The refrigerant gas gives up both sensible heat and
large amounts of latent heat energy to the cooler
ambient air.
•The gas cools, changes state and condenses to a
liquid.
•The refrigerant leaves the condenser as a very warm
high pressure liquid.
The DME controls system cooling fans based on engine
load. When the A/C is ON, the electric cooling fan comes
ON to improve airflow and heat transfer.
Receiver/Dryer
911 Carrera (996) Receiver/Dryer
The receiver/dryer is a reservoir for refrigerant on the
system high pressure side. It is located between the
condenser outlet and evaporator inlet. Condensed liquid
refrigerant flows into the receiver dryer from the
condenser.
As heat load on the A/C system changes, more or less
refrigerant will be in the liquid state. Also, over time, some
refrigerant will escape past seals. The receiver/dryer acts
as a reservoir for refrigerant to compensate for these
conditions. The pickup tube in the receiver/dryer ensures
that only liquid refrigerant is sent to the expansion valve.
The receiver/dryer contains a desiccant to remove
moisturefrom the system. The desiccant can absorb 6-12
gof water.This is not much, and moisturemust be kept
out of the system during repairs.
R-12 systems included a sight glass on top of the
receiver/dryer The flow of liquid refrigerant could be seen
through the glass and a stream of bubbles indicated low
refrigerant level. A sight glass was used on some R-134a
systems in the early 1990’s. A/C service equipment accu-
rately measures the refrigerant charge by weight, making
the sight glass unnecessary.
When retrofitting an R-12 system with R-134a, always
replace the receiver/dryer as R-12 desiccants arenot
compatible with R-134a, and the desiccant will be perma-
nently saturated with mineral oil.

Page 1.12 Climate Control Systems Diagnosis & Repair
Air Conditioning Basics
Evaporator
The evaporator is a heat exchanger located in air distribu-
tion housing. It has tubes and fins similar to a radiator or
condenser and it has a large surface area for efficient heat
transfer.The evaporator permits cold refrigerant to
absorb heat from warm air in the passenger
compartment. Outside air or recirculated air is forced
through the air distribution housing and evaporator fins by
blowers.
The evaporator is on the A/C system low pressure side.
The thermostatic expansion valve (TEV) is a restriction
controlling how much refrigerant enters the evaporator.
The refrigerant changes state in the evaporator in this
sequence:
•Liquid high pressure refrigerant sprays into the evapo-
rator, controlled by the TEV orifice.
•The pressure of the refrigerant drops as it passes
through this orifice. At this low pressure, the refrigerant
temperatureis above its boiling point. The refrigerant
boils rapidly and changes state.
•As the refrigerant becomes a gas, it absorbs both
sensible heat and large amounts of latent heat from the
cabin air passing through the evaporator fins.
•The refrigerant warms and the cabin air passing over
the evaporator fins cools.
•The refrigerant leaves the evaporator as a cool low
pressure gas, pulled by the suction (intake) side of the
compressor. This low side pressure will be approx. 2
bar (30 psi). Check workshop manuals for exact system
pressure specifications.
In addition to removing heat, the evaporator also dehumidi-
fies the interior air. Cool air cannot hold as much moisture
as warm air. As the air is cooled, moisture condenses and
collects on the evaporator fins. Dehumidifying the air adds
to passenger comfort and also helps to demist the wind-
shield in damp weather. This is why A/C is enabled when
the defrost function is selected.
Evaporator fin temperatures cannot be allowed to drop
below the freezing point of water, 0° C (32° F), or the
condensation can freeze and ice buildup can block the
evaporator fins. Dust and matter carried in with the
airstream tends to collect on the wet evaporator fins, so
there is a cleaning effect. The condensed water that
collects on the evaporator fins is allowed to drain.
Notes:

Air Conditioning Basics
Climate Control Systems Diagnosis & Repair Page 1.13
Thermostatic Expansion Valve (TEV)
The Thermostatic Expansion Valve (TEV) is located at the
evaporator inlet. It separates the high and low pressure
sides of the system and creates the restriction that the
compressor uses to build high side pressure. High
pressure liquid refrigerant flows to the expansion valve
inlet from the receiver/dryer.
Porsche uses the H-Type block expansion valve. This valve
works the same way as the old style right-angle valve with
external sensing tubes, but is internally compensated
within the valve and has no external lines to the
evaporator.
The TEV has a variable orifice which controls the amount
of refrigerant admitted into the evaporator. High pressure
liquid refrigerant passes through the TEV orifice at the
evaporator inlet. The liquid refrigerant sprays into the
evaporator where it is exposed to low pressure and rapidly
evaporates. The TEV senses both temperatureand
pressure in the evaporator. Both evaporator inlet and
outlet lines pass through the TEV. Refrigerant temperature
is sensed at the evaporator outlet. Increases in evaporator
outlet gas temperaturedue to increased heat load cause
the diaphragm in the gas filled thermostatic valve element
to move downward, opening the ball valve a greater
amount against spring tension and admitting more refrig-
erant.
The expansion valve also senses evaporator inlet
pressure. Pressure acts on the underside of the
diaphragm in the gas filled thermostatic valve element.
Any decrease in evaporator pressuretends to open the
ball valve and increase the amount of refrigerant admitted.
This would be the case if the evaporator were "starved"
and required more refrigerant. When additional refrigerant
flows into the evaporator, more refrigerant is available to
absorb heat. This reduces the temperature at the
evaporator outlet, causing a pressuredrop in the thermo-
static valve element and increases evaporator pressure.
Both conditions act on the diaphragm to reduce the ball
valve opening. The cross-section opening of the valve is
reduced as the spring pushes the ball valve toward its
seat.
Notes:

Page 1.14 Climate Control Systems Diagnosis & Repair
Air Conditioning Basics
Lines and Hoses
A/C system components are connected by rigid lines and
flexible hoses. This creates the closed loop through which
the refrigerant flows. Rigid lines are formed aluminum. The
flexible hoses are a reinforced rubber compound with a
barrier liner.
Low pressure lines and hoses are generally larger in
diameter when compared with high pressure lines and
hoses. This is because refrigerant gas in the low side has
expanded and takes up much more space than either
refrigerant gas or liquid on the high side.
Joints may be several types but always have o-rings for
sealing. When assembling lines or replacing o-ring seals,
always lubricate o-rings only with PAG oil. The oil helps the
o-ring to properly seat and seal. Do not use any other
lubricant. Always torque fasteners to specifications.
Service Connections
911 Carrera (993) models have A/C high and low side
service connections located in the rear near the A/C
compressor.
911 Carrera (996)/(997) and Boxster (986)/(987) model connec-
tions are located in the cowl area on the right side, near the
battery and expansion valve.
Cayenne model service connections are in front in the engine
compartment on the left side.
R-134a service connection fittings are quick-connect style
and aredifferent from those on R-12 systems. This was
done to prevent cross-contamination of refrigerants which
cannot be mixed. R-134a quick connect fittings are
different sizes for the high and low sides. This ensures
that the low side and high side service hoses are properly
connected to their respective ports. Disconnecting an R-
134a service hose quick-connector automatically seals the
ports to retain the refrigerant in the vehicle’s system and
also in the service hose.
R-12 systems use threaded service connection fittings and
hand shut-offvalves. By law,the shut-offvalves must be no
more than 30 cm (12 in.) from the end of the service hose
to reduce refrigerant loss.