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downstream of evaporator reaches the specified value (ap‐
proximately 2 to 5° C):
♦ A value greater than 75% (0.55 A) will be displayed in the
measured values block for the A/C compressor regulator valve
Climatronic control module after starting the vehicle, depend‐
ing on the measured temperature, engine RPM and the elec‐
trical system voltage. As soon as temperature measured by
the evaporator vent temperature sensor -G263- approximates
the specified value, the activation is rescinded and thus the
compressor output is reduced. Refer to -VAS5051B- under
"Guided Fault Finding."
♦ Under certain operating conditions, residual moisture in re‐
frigerant circuit can lead to an ice build-up at A/C Compressor
Regulator Valve -N280- (and at expansion valve). A/C com‐
pressor control is reduced by this ice build-up, evaporator is
cooled too intensely and freezes. The freeze-up of the evap‐
orator can be the cause for the following customer complaints.
– After a long drive, A/C system repeatedly or sporadically fails
(no cooling or heating performance), after switching off vehicle
and after a short time, A/C function is OK again.
– After a long drive, windows fog up from inside, windows are
also not cleared by then pressing the “Defrost“ button, after
switching off vehicle and after a short time, A/C function is OK
again.
Corrective action:
– Check the measured value from the evaporator vent temper‐
ature sensor -G263- with the “Read measuring value block“
function using -VAS5051B- under "Guided Fault Finding."
– If the sensor measured is too high under the operating condi‐
tions reported by the customer (even though the A/C system
is operating without difficulty at greater than e.g. 10° C, de‐
pending on ambient temperature), check the evaporator vent
temperature sensor (an incorrect measured value may cause
evaporator the ice up).
– When the measured value from the sensor is below the oper‐
ating condition described by the customer (at a temperature
above 0° C, longer when it is lower than 0° C). Bring vehicle
to a workshop that has the necessary tools and in which the
work can be performed accordingly by qualified personnel.
Refer to ⇒ Refrigerant R134a Servicing; Rep. Gr. 00 ; General
Information . Bring the problems determined to the attention
of the workshop.
– Check refrigerant line from evaporator (from expansion valve)
to A/C compressor (thick tube, low pressure side) with engine
running. If this line is thickly iced-up when a problem occurs (a
very thin layer of ice is permitted), this indicates that the tem‐
perature in the evaporator is too low. Bring vehicle to a work‐
shop that has the necessary tools and in which the work can
be performed accordingly by qualified personnel. Refer to ⇒
Refrigerant R134a Servicing; Rep. Gr. 00 ; General Informa‐
tion . (it is possible that A/C compressor regulation is not OK).
Bring the problems determined to the attention of the work‐
shop.
4.3
Causes of Odor
♦ Smells like burnt oil.
– Mostly forms in the engine compartment due to leaks on the
engine or transmission.
♦ Sulphurous smell similar to exhaust.
– Due to leaks in the exhaust system.
Audi TT 2007 ➤
Heating, Ventilation and Air Conditioning - Edition 01.2011
4. Diagnosis and Testing
89
