Get Checking pressures -> Checking pressures - vehicles with restrictor, reservoir and air conditioner compressor regulating valve N280 (with externally regulated air conditioner compressor) Guide for Audi A2 SUV 1999-2005

Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...

Air conditioner with refrigerant R134a - Edition 11.2018

8.4

Checking pressures - vehicles with re‐

strictor, reservoir and air conditioner

compressor regulating valve - N280-

(with externally regulated air conditioner

compressor)

Note

♦ Connect air conditioner service station ⇒ page 187 .

♦ Observe test requirements ⇒ page 193 .

– Check the pressures in the refrigerant circuit (with the air con‐

ditioner service station) with the ignition switched off

⇒ page 195 .

The pressures with the ignition switched off correspond to the

specifications.

– Start engine.

– Set engine speed to 2000 rpm.

– Observe the pressure reading (e.g. pressure gauge) of the air

conditioner service station.

Note

♦ The switching pressures for actuation of -N280- and the radi‐

ator fans - V7- are vehicle-specific.

♦ Measure the pressures at the service connections; the fitting

locations of these connections are vehicle-specific ⇒ Heating,

air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-spe‐

cific Workshop Manual).

⇒ “8.4.1 Specifications for pressures in refrigerant circuit”,

page 212

8.4.1

Specifications for pressures in refriger‐

ant circuit

High-pressure side:

Increasing from initial pressure (on connection of pressure

gauges) up to 20 bar

212

Rep. gr.87 - Air conditioning system

Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...

Air conditioner with refrigerant R134a - Edition 11.2018

Low-pressure side:

Decreasing from initial pressure (on connecting pressure gauges)

to value in graph

A - Low pressure (measured at service connection) in bar abso‐

lute pressure.

B - Control current for air conditioner compressor regulating valve

- N280- in amps

C - Permissible tolerance range

8. Checking pressures

213

Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...

Air conditioner with refrigerant R134a - Edition 11.2018

Note

♦ In the event of a very high cooling output requirement (e.g.

high ambient temperature and high fresh air blower speed at

low engine speed), the air conditioner compressor cannot in‐

itially set the pressure on the low-pressure end to the value

-C- given in the graph (e.g. for a certain time after switching

on the air conditioner). The air conditioner compressor is ac‐

tuated with the maximum specified control current, however

the delivery volume of the air conditioner compressor is no

longer sufficient under these ambient conditions and at this

engine speed to reduce the pressure on the low-pressure end

to the value in the graph. One way of checking the control ac‐

tion of the air conditioner compressor under these conditions

is to activate the fresh air blower with only approx. 40% of the

maximum voltage and to check the pressures at reduced fresh

air blower speed ⇒ Vehicle diagnostic tester (“self-diagnosis”

or “Guided Fault Finding” function for air conditioner) and ⇒

Heating, air conditioning; Rep. gr. 00 ; Repair instructions;

Checking cooling output or ⇒ Heating, air conditioning; Rep.

gr. 87 ; Refrigerant circuit (vehicle-specific Workshop Man‐

ual).

♦ Under unfavourable conditions (very high ambient tempera‐

tures, high humidity), pressure on high-pressure end may

increase to max. 29 bar.

♦ Control current -B- is displayed in measured value block of

operating and display unit for front air conditioning system -

E87- or operating and display unit ( Climatronic control unit -

J255- ).

♦ The pressure in the refrigerant circuit measured by the high-

pressure sender - G65- or the refrigerant pressure and tem‐

perature sender - G395- is displayed in the measured value

block of -E87- or of the operating and display unit ( Climatronic

control unit - J255- ) ⇒ Vehicle diagnostic tester (“Self-diag‐

nosis” or “Guided Fault Finding” function for air conditioner)

and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant cir‐

cuit (vehicle-specific Workshop Manual).

♦ The low pressure settles as a function of the control current

for the air conditioner compressor regulating valve - N280-

within the air conditioner compressor output range in the tol‐

erance band.

♦ Under unfavourable conditions (very high ambient tempera‐

tures, high humidity), the air conditioner compressor output

may not always be sufficient to attain the specified value.

♦ If the compressor capacity utilisation is greater than 90 %, the

pressure on the low-pressure end may be in excess of the

tolerance range “C” shown in the graph (the compressor out‐

put no longer suffices).

♦ The specified operating current for the regulating valve must

be greater than 0.3 A to ensure reliable actuation of the regu‐

lating valve.

♦ “0 bar absolute pressure” corresponds to an absolute vacuum.

Normal ambient pressure corresponds to an absolute pres‐

sure of 1 bar. On the scales of most pressure gauges, 0 bar

corresponds to an absolute pressure of one bar (can be seen

from “-1 bar” mark below “0”).

214

Rep. gr.87 - Air conditioning system

Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...

Air conditioner with refrigerant R134a - Edition 11.2018

♦ In the "maximum cooling output" setting, the control current is

regulated to approx. 0.65 (up to 0.85 A for specific vehicles);

this is displayed in the measured value block ⇒ Vehicle diag‐

nostic tester (“Self-diagnosis” or “Guided Fault Finding” func‐

tion for air conditioner) and ⇒ Heating, air conditioning; Rep.

gr. 00 ; Repair instructions; Checking cooling output or ⇒

Heating, air conditioning; Rep. gr. 87 ; Overview of fitting lo‐

cations - air conditioner (vehicle-specific Workshop Manual).

Possible deviation from

specification

Possible causes of fault

Fault elimination

•

High pressure remains

constant or only increa‐

ses slightly (above pres‐

sure with engine stop‐

ped)

♦ Actuation of air conditioner com‐ – Check activation of -N280- ⇒ Heat‐

pressor regulating valve - N280-

not OK

ing, air conditioning; Rep. gr. 87 ;

Refrigerant circuit (vehicle-specific

Workshop Manual).

♦ Not enough refrigerant in circuit

– Locate leak with leak detector and

repair it.

•

Low pressure quickly

drops to value in graph or

below

– Re-charge refrigerant circuit.

Required cooling output

is not attained.

•

High pressure normal

Low pressure too low

(see graph)

•

Required cooling output

is not attained.

Note

If no fault is found for this problem, clean refrigerant circuit (by

flushing with refrigerant R134a ⇒ page 100 or blowing out with

compressed air and nitrogen ⇒ page 95 ).

Possible deviation from spec‐

ification

Possible causes of fault

Fault elimination

•

High pressure does not

rise or only rises slightly

above the pressure with

the engine stopped.

♦ No actuation of the air conditioner – Check actuation and drive of the air

compressor ( air conditioner

compressor regulating valve -

N280- )

conditioner compressor and perform

repair ⇒ Heating, air conditioning;

Rep. gr. 87 ; Air conditioner com‐

pressor (vehicle-specific Workshop

Manual).

•

Low pressure does not

♦ The air conditioner compressor is

not driven.

drop or only drops slightly.

– Check actuation and operation of -

N280- .

Required cooling output is

not attained.

♦ Constriction or blockage in refrig‐ – Clean refrigerant circuit (flush with

erant circuit (e.g. in refrigerant

line between service connection

on low-pressure side and air con‐

ditioner compressor).

refrigerant R134a ⇒ page 100 or

blow out with compressed air and ni‐

trogen ⇒ page 95 ).

– Renew hose or pipe if kinked or con‐

stricted.

♦ Air conditioner compressor regu‐ – Check operation of -N280- , remove

lating valve - N280- defective

-N280- if applicable and check for

contamination ⇒ page 285 .

8. Checking pressures

215

Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...

Air conditioner with refrigerant R134a - Edition 11.2018

Possible deviation from spec‐

Possible causes of fault

Fault elimination

ification

♦ Air conditioner compressor de‐ – Renew air conditioner compressor.

fective

Possible deviation from spec‐

ification

Possible causes of fault

Fault elimination

•

High pressure increases ♦ Actuation of air conditioner com‐ – Check activation of -N280- ⇒ Heat‐

above specification

Low pressure quickly

pressor regulating valve - N280-

not OK

ing, air conditioning; Rep. gr. 87 ;

Refrigerant circuit (vehicle-specific

Workshop Manual).

•

drops to value in graph or ♦ Constriction or blockage in refrig‐

below

erant circuit

– Run hand over refrigerant circuit to

check for differences in temperature.

•

Required cooling output is

not attained.

•

If there is a difference in temperature

at one component:

– Renew hose or pipe if kinked or con‐

stricted.

– Flush the refrigerant circuit with com‐

pressed air and nitrogen in the event

of an obstruction.

•

If no fault is found:

– Clean refrigerant circuit (flush with

refrigerant R134a ⇒ page 100 or

blow out with compressed air and ni‐

trogen ⇒ page 95 ).

Possible deviation from spec‐

ification

Possible causes of fault

Fault elimination

•

High and low pressure

normal at first, after some

time high pressure increa‐

ses above specification

and

♦ Actuation of air conditioner com‐ – Check activation of -N280- ⇒ Heat‐

pressor regulating valve - N280-

not OK

ing, air conditioning; Rep. gr. 87 ;

Refrigerant circuit (vehicle-specific

Workshop Manual).

– Renew reservoir (with dryer) and

evacuate refrigerant circuit for at

least 3 hours (see note).

•

Low pressure drops to val‐

ue in graph or below

Required cooling output is

no longer attained.

♦ Air conditioner compressor regu‐ – Check operation of -N280- , remove

•

High and low pressure

normal at first

lating valve - N280- defective

-N280- if applicable and check for

contamination ⇒ page 285 .

After lengthy operating pe‐

riod, low pressure drops

excessively (evaporator

ices up)

♦ Moisture in refrigerant circuit

– Clean refrigerant circuit (flush with

refrigerant R134a ⇒ page 100 or

blow out with compressed air and ni‐

trogen ⇒ page 95 ).

216

Rep. gr.87 - Air conditioning system

Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...

Air conditioner with refrigerant R134a - Edition 11.2018

Note

♦ It is not initially necessary to clean the refrigerant circuit (flush

with refrigerant R134a ⇒ page 100 or blow out with com‐

pressed air and nitrogen ⇒ page 95 ) when this problem

occurs. Normally, there is only a small quantity of moisture in

the system which can be removed by lengthy evacuation.

♦ If an issue involving moisture in the refrigerant circuit only oc‐

curs after a lengthy operating period or only infrequently (low

pressure drops below specified value and evaporator ices up),

it is sufficient to renew the dryer (adjust quantity of refrigerant

oil). Subsequently, evacuate refrigerant circuit for at least 3

hours.

♦ A problem with evaporator output temperature sender - G263-

can also cause icing-up of refrigerant circuit. If this problem

occurs, you should also check the measured value of the

evaporator output temperature sender - G263- ⇒ Vehicle di‐

agnostic tester (“Self-diagnosis” or “Guided Fault Finding”

function for air conditioner) and ⇒ Heating, air conditioning;

Rep. gr. 00 ; Repair instructions; Checking cooling output or

⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit

(vehicle-specific Workshop Manual).

Possible deviation from spec‐

ification

Possible causes of fault

Fault elimination

•

High pressure normal

♦ Actuation of air conditioner com‐ – Check activation of -N280- ⇒ Heat‐

pressor regulating valve - N280-

not OK

ing, air conditioning; Rep. gr. 87 ;

Refrigerant circuit (vehicle-specific

Workshop Manual).

Low pressure too low (see

graph)

♦ Air conditioner compressor regu‐

lating valve - N280- defective

•

Required cooling output is

attained.

– Check operation of -N280- , remove

-N280- if applicable and check for

contamination ⇒ page 285 .

♦ Air conditioner compressor de‐ – Clean refrigerant circuit (flush with

fective

refrigerant R134a ⇒ page 100 or

blow out with compressed air and

nitrogen ⇒ page 95 ).

– Renew air conditioner compressor.

Note

Observe the following regarding fault “High pressure normal, low

pressure too low”: This fault may cause the evaporator to ice up

although the amount of refrigerant in the circuit is OK. Check

measured values of evaporator output temperature sender -

G263- and actuation of air conditioner compressor regulating

valve - N280- . If the measured value of the evaporator output

temperature sender - G263- is incorrect, the evaporator may ice

up or the cooling output may not be attained ⇒ Vehicle diagnostic

tester (“Self-diagnosis” or “Guided Fault Finding” function for air

conditioner) and ⇒ Heating, air conditioning; Rep. gr. 00 ; Repair

instructions; Checking cooling output or ⇒ Heating, air condition‐

ing; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific Workshop

Manual).

8. Checking pressures

217

Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...

Air conditioner with refrigerant R134a - Edition 11.2018

Possible deviation from spec‐

ification

Possible causes of fault

Fault elimination

•

High pressure normal or ♦ Actuation of air conditioner compressor – Check activation of -N280- ⇒

too high

regulating valve - N280- not OK

♦ Too much refrigerant in circuit

Heating, air conditioning;

Rep. gr. 87 ; Refrigerant cir‐

cuit (vehicle-specific Work‐

shop Manual).

Low pressure too high

(see graph)

Noise from air conditioner

compressor (particularly

after being switched on)

– Extract refrigerant from refrig‐

erant circuit.

•

If amount of refrigerant ex‐

tracted roughly corresponds

to specified capacity:

•

Required cooling output is

not attained.

– Renew air conditioner com‐

pressor.

•

The quantity of refrigerant ex‐

tracted is significantly greater

than the prescribed charge

quantity.

– Re-charge refrigerant circuit.

– Repeat test.

•

High and low pressure

normal

♦ Actuation of air conditioner compressor – Check actuation of -N280- .

regulating valve - N280- not OK

– Discharge refrigerant circuit.

Required cooling output is ♦ Too much refrigerant oil in circuit

not attained.

– Clean refrigerant circuit (flush

with refrigerant R134a

•

High and low pressure

normal.

⇒ page 100 or blow out with

compressed air and nitrogen

⇒ page 95 ).

Air conditioner compres‐

sor noise (particularly after

switch-on).

•

Required cooling output is

attained.

Note

♦ Overfilling with refrigerant oil may occur if, for example, the air

conditioner compressor has been renewed without adjusting

the quantity of refrigerant oil.

♦ If there is too much refrigerant oil in the circuit, discharge the

air conditioner compressor and renew the receiver. After

cleaning the refrigerant circuit (flush with refrigerant R134a

⇒ page 100 or blow out with compressed air and nitrogen

⇒ page 95 ), add the correct amount of refrigerant oil to the

circuit ⇒ page 333 .

218

Rep. gr.87 - Air conditioning system

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