clutch AUDI A4 1998 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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87-23


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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87-25

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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87-30

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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