AUDI A4 1997 B5 / 1.G Refrigerant System Components Workshop Manual

87-21


Refrigerant system (R-134a),
components

A/C compressor


The compressor is driven via a belt on the engine when the A/C clutch
engages (A/C ON).
Low pressure refrigerant gas from the evaporator is compressed by the
compressor. After compression, the refrigerant gas (now high pressure)
flows to the condenser.
The variable displacement A/C compressor varies piston stroke and
output depending on load requirements and suction pressure.
Notes:
Zexel A/C compressors were installed from start of production. During
m.y. 1996, Nippondenso (Denso) type compressors are installed as a
running change. These compressors are not equipped with A/C speed
sensor G111. The compressor contains PAG type refrigerant oil that is mixable
under all temperatures with refrigerant R-134a. A label on the compressor indicates that compressor is for R-134a
systems only.
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87-22

Valve connections for pressure
switches


A Schrader valve is installed under A/C system pressure switches to allow
replacement without discharging the refrigerant system.
Note:
A/C system switches are available in different versions. Always refer to
the latest parts information to ensure correct switch application. - A/C system low and high pressure switches use different size threads.
- Use only the correct switches and O-ring seals specified for use with R-
134a refrigerant and PAG oil.
A - Switch connection (soldered)
B - O-ring seal
C - Schrader valve insert
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87-23


A/C compressor speed sensor -G111-, (Zexel compressors
only)

Note: - Inductive sensor (4 pulses per compressor rotation)
- Determines A/C compressor speed; the A/C compressor clutch control
module (Manual A/C) or the A/C control head (Automatic climate
control) compares compressor speed to engine speed and calculates
belt slippage (as a percentage) and switches compressor OFF if
slippage is too large (for example, if belt is too loose.)
A/C compressor speed sensor -G111- is not installed on Nippondenso
compressors. A thermo-fuse is incorporated into the clutch coil of Nippondenso
compressors. Current to the clutch coil is interrupted in the event of
compressor overheating.
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87-24

Pressure relief valve


The pressure relief valve is mounted on the compressor. At approx. 38
bar (551 psi), the valve opens to vent excessive pressure. When system
pressure is reduced to approx. 30-35 bar (435-508 psi), the valve closes
to prevent total refrigerant loss.
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87-25

A/C refrigerant high pressure switch -
F23- and A/C clutch switch -F118-


Note:
Beginning with m.y. 1997, A/C pressure switch -
F129- replaces pressure switches -F23-, and -
F118- page 87
-67
.

Both switches are incorporated into a single housing.
F23 function
F 118 function - Switches coolant fan (V7) to second speed when A/C system pressure
increases.
- Switches A/C clutch -N25- OFF if system pressure is too high.
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87-26

High pressure service valve assembly


Notes: A - Service valve connection (located on condenser inlet line)
B - Schrader valve insert
C - O-ring seal
D - Cap with seal
Only a high pressure service valve is used for A/C system servicing. A
low pressure service valve is not installed in the A/C system. Perform
all A/C system service operations (i.e discharging, evacuating, and
charging) through the high pressure service valve only. Use only the specified R-134a quick coupling connectors when
servicing the refrigerant system. Before removing the valve insert from the high pressure service valve,
discharge refrigerant system page 87
-201
.
Always reinstall cap -D- over service valve.Illustration shows the condenser from an Audi 100 model.
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87-27

Condenser


The condenser transfers heat from the compressed refrigerant gas to the
outside air which causes the refrigerant to change state from a gas to a
liquid.
Note:
Illustration shows the condenser from an Audi 100 model.
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87-28

Restrictor


The restrictor restricts and controls refrigerant flow to the evaporator thus
lowering refrigerant temperature and pressure.
Upstream of the restrictor, the refrigerant is hot and under high pressure.
Downstream of the restrictor, the refrigerant is cold and under low
pressure.
A strainer located upstream of the restrictor filters out any dirt or particles.
Another strainer located downstream of the restrictor atomizes the
refrigerant before it enters the evaporator.
Notes:
Insert restrictor so that Arrow -A- points to evaporator.Illustration shows the evaporator from an Audi 90 model.
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87-29

Evaporator


Liquid refrigerant entering the evaporator absorbs heat from air passing
through the evaporator fins and cools the air. As the refrigerant absorbs
heat it turns to vapor and then is suctioned by the compressor.
Note:
Illustration shows the evaporator from an Audi 90 model.
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87-30

A/C refrigerant low pressure switch -
F73-


Function

Switches A/C Clutch -N25- OFF if system suction pressure is too low (low
refrigerant charge). This switch protects the compressor if the refrigerant
system is empty.
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