Get Checking pressures -> Checking pressures - vehicles with expansion valve, receiver 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

8.5

Checking pressures - vehicles with ex‐

pansion valve, receiver and air condi‐

tioner compressor regulating valve -

N280- (with externally regulated air

conditioner compressor)

Note

♦ Connect air conditioner service station ⇒ page 187 .

♦ Observe test requirements ⇒ page 193 .

♦ If problems are only encountered at one evaporator on vehi‐

cles fitted with two evaporators, check whether the pressures

in the refrigerant circuit are OK. Check for cross-sectional re‐

striction or blockage of line connection between faulty evapo‐

rator and outgoing line connection at refrigerant line distribu‐

tion point. If no fault is found, discharge the refrigerant circuit

and re-fill it with the specified quantity of refrigerant. Then

check the pressures and the cooling output of the air condi‐

tioner again. If the problem persists, renew the expansion

valve upstream of the faulty evaporator ⇒ Heating, air condi‐

tioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific Work‐

shop Manual).

– 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 the air conditioner

compressor regulating valve - N280- and the radiator 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).

⇒ “8.5.1 Specifications for pressures in refrigerant circuit”,

page 219

8.5.1

Specifications for pressures in refriger‐

ant circuit

High-pressure side:

Increasing from initial pressure (when connecting pressure

gauges) up to max. 20 bar

8. Checking pressures

219

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

Air conditioner with refrigerant R134a - Edition 11.2018

Low pressure:

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 (applicable to compressor ca‐

pacity utilisation of 10...90 %).

220

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

♦ 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), the pressure on the high-pressure side

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 Climatronic control unit - J255- .

♦ High pressure measured by the high-pressure sender - G65-

(or refrigerant pressure and temperature sender - G395- /

pressure sender for refrigerant circuit - G805- ) is displayed as

a measured value of -E87- or of the air conditioning system

control unit - J301- / operating and display unit ( Climatronic

control unit - J255- ).

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

for the air conditioner compressor regulating valve - N280- and

the control characteristic of the expansion valve within the air

conditioner compressor output range in the tolerance 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 air conditioner com‐

pressor regulating valve - N280- must be greater than 0.3 A to

ensure reliable valve actuation.

♦ In the “maximum cooling output” setting, the control current for

the air conditioner compressor regulating valve - N280- is

regulated to approx. 0.65 A (up to 0.85 A). This measured val‐

ue is vehicle-specific and displayed in the measured value

block.

8. Checking pressures

221

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

Air conditioner with refrigerant R134a - Edition 11.2018

♦ On the absolute pressure scale, 0 bar corresponds to an ab‐

solute vacuum. Normal ambient pressure corresponds to an

absolute pressure of 1 bar. On the scale of most pressure

gauges, 0 bar corresponds to an absolute pressure of 1 bar

(can be seen from -1 bar mark below 0) ⇒ 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 Manual).

Possible deviation from speci‐

fication

Possible causes of fault

Fault elimination

•

High pressure remains con‐ ♦ Actuation of air conditioner compres‐ – Check activation of -N280- ⇒

stant or only increases

slightly (above pressure

with engine stopped)

sor regulating valve - N280- not OK

♦ Not enough refrigerant in circuit

♦ Expansion valve defective

Heating, air conditioning;

Rep. gr. 87 ; Refrigerant cir‐

cuit (vehicle-specific Work‐

shop Manual).

•

Low pressure quickly drops

to value in graph or below

– Extract refrigerant from re‐

frigerant circuit.

Required cooling output is

not attained.

•

If quantity of refrigerant ex‐

tracted is substantially less

than specified capacity:

– Locate leak with leak detec‐

tor and repair it.

•

High pressure normal

Low pressure in line with

value in graph

– Re-charge refrigerant circuit.

– Repeat test.

•

Required cooling output is

not attained.

•

If amount of refrigerant ex‐

tracted roughly corresponds

to specified capacity:

•

High pressure normal

Low pressure too low (see

graph)

– Renew expansion valve.

– Re-charge refrigerant circuit.

– Repeat test.

•

Required cooling output is

not attained.

222

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

♦ 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 ).

♦ Check the measured values of the evaporator output temper‐

ature sender - G263- and actuation of -N280- . If the measured

value of the evaporator output temperature sender - G263- is

not OK, the evaporator may ice up or the cooling output is not

attained.

♦ If, after renewing the expansion valve, operation of the air

conditioning system is not OK when the test is repeated (re-fit

old expansion valve), clean the refrigerant circuit (flush with

refrigerant R134a ⇒ page 100 or blow out with compressed air

and nitrogen ⇒ page 95 ). Then renew the air conditioner com‐

pressor and receiver.

♦ In this case, the evaporator may ice up although the amount

of refrigerant in the refrigerant circuit is OK.

♦ If the expansion valve is defective (permanently closed or

does not open sufficiently), -N280- is actuated to maximum

output and the low pressure drops to the value in the graph or

below (the air conditioner compressor draws off refrigerant

from the low-pressure end). However, as refrigerant cannot

flow via the expansion valve, the cooling output is not attained

and the high pressure may also not increase or only increase

slightly since there is no energy exchange ⇒ 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 ; Refrigerant circuit (ve‐

hicle-specific Workshop Manual).

Possible devia‐ Possible causes of

Fault elimination

tion from specifi‐

cation

fault

•

High pres‐

sure does not

rise or only

rises slightly

above the

♦ No actuation of – Check actuation

the air condition‐

er compressor

( air conditioner

compressor regu‐

lating valve -

and drive of the air

conditioner com‐

pressor and per‐

form repair ⇒ Heat‐

ing, air condition‐

ing; Rep. gr. 87 ; Air

conditioner com‐

pressor (vehicle-

specific Workshop

Manual).

pressure with

the engine

stopped.

N280- )

♦ The air condition‐

er compressor is

not driven.

•

Low pressure

does not drop

or only drops

slightly.

Required

cooling out‐

put is not at‐

tained.

♦ Air conditioner

compressor regu‐

lating valve -

– Check operation of

-N280- , remove -

N280- if applicable

and check for con‐

tamination

N280- defective.

⇒ page 285 .

8. Checking pressures

223

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

Air conditioner with refrigerant R134a - Edition 11.2018

Possible devia‐ Possible causes of

Fault elimination

tion from specifi‐

cation

fault

♦ Constriction or

blockage in re‐

frigerant circuit

(e.g. in refrigerant

line between

– Clean refrigerant

circuit (flush with re‐

frigerant R134a

⇒ page 100 or blow

out with com‐

service connec‐

tion on low-pres‐

sure side and air

pressed air and ni‐

trogen ⇒ page 95 ).

conditioner com‐ – Renew hose or pipe

pressor).

if kinked or constric‐

ted.

♦ Air conditioner

compressor de‐

fective

– Renew air condi‐

tioner compressor.

Note

♦ In the event of this problem, make sure the air conditioner

compressor (air conditioner compressor shaft) is actually be‐

ing driven via the pulley/drive unit ⇒ Heating, air conditioning;

Rep. gr. 87 ; Air conditioner compressor (vehicle-specific

Workshop Manual).

♦ As of Model Year 2012, air conditioner compressors with both

-N280- and an air conditioning system magnetic clutch - N25-

fitted at the pulley are to be introduced for certain engines and

models. In the event of this problem, make sure -N25- is ac‐

tually being actuated and that the air conditioner compressor

(air conditioner compressor shaft) is being driven via the pulley

⇒ Heating, air conditioning; Rep. gr. 87 ; Air conditioner com‐

pressor (vehicle-specific Workshop Manual) and ⇒ Electronic

parts catalogue .

224

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

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

pressor regulating valve - N280-

not OK

ing, air conditioning; Rep. gr. 87 ;

Refrigerant circuit (vehicle-specific

Workshop Manual).

Low pressure quickly

drops to value in graph

♦ Constriction or blockage in refrig‐

erant circuit

– Run hand over refrigerant circuit to

check for differences in temperature.

Required cooling output is

not attained.

♦ Expansion valve defective

•

If there is a difference in temperature

at one component:

– Renew hose or pipe if kinked or con‐

stricted.

– In the event of clogging, clean refrig‐

erant circuit (flush with refrigerant

R134a ⇒ page 100 or blow out with

compressed air and nitrogen

⇒ page 95 ).

– Re-charge refrigerant circuit.

– Repeat test.

•

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 ).

– Re-charge refrigerant circuit.

– Repeat test if operation is not OK:

– Renew expansion valve and receiv‐

er.

8. Checking pressures

225

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

Air conditioner with refrigerant R134a - Edition 11.2018

Note

♦ If the function of the air conditioning system is not OK when

the test is repeated, renew expansion valve and receiver.

♦ In this case, the evaporator may ice up although the amount

of refrigerant in the refrigerant circuit is OK.

♦ If the expansion valve is defective (permanently closed or

does not open sufficiently), the air conditioner compressor

regulating valve - N280- is actuated to maximum output and

the low pressure drops to the value in the graph or below (the

air conditioner compressor draws off refrigerant from the low-

pressure end). However, as refrigerant cannot flow via the

expansion valve, the cooling output is not attained and the high

pressure may also not increase or only increase slightly since

there is no energy exchange ⇒ Vehicle diagnostic tester

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

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

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

tioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific Work‐

shop Manual).

♦ 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 .

Possible deviation from speci‐

fication

Possible causes of fault

Fault elimination

•

High and low pressure nor‐ ♦ Actuation of air conditioner compres‐ – Check activation of -N280- ⇒

mal at first, but after a while:

sor regulating valve - N280- not OK

Heating, air conditioning;

Rep. gr. 87 ; Refrigerant cir‐

cuit (vehicle-specific Work‐

shop Manual).

High pressure rises above ♦ Moisture in refrigerant circuit

specified value

Low pressure drops to val‐

ue in graph or below

– Clean refrigerant circuit

(flush with refrigerant R134a

⇒ page 100 or blow out with

compressed air and nitrogen

⇒ page 95 ).

Required cooling output is

no longer attained.

– Renew receiver with dryer.

•

High and low pressure nor‐

mal at first

– Evacuate refrigerant circuit

for at least 3 hours.

After lengthy driving time,

low pressure drops below

specification (evaporator

ices up)

– Re-charge refrigerant circuit.

– Repeat test.

♦ Air conditioner compressor regulating – Check operation of -N280- ,

valve - N280- defective

remove -N280- if applicable

and check for contamination

⇒ page 285 .

226

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 in the receiver (adjust quantity

of refrigerant oil). Subsequently, evacuate refrigerant circuit

for at least 3 hours.

♦ In this case, the evaporator may ice up although the amount

of refrigerant in the refrigerant circuit is OK.

♦ 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 speci‐

fication

Possible causes of fault

Fault elimination

•

High pressure normal

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

sor regulating valve - N280- not OK

Heating, air conditioning;

Rep. gr. 87 ; Refrigerant cir‐

cuit (vehicle-specific Work‐

shop Manual).

•

Low pressure too low (see

graph)

•

Required cooling output is

attained.

– Clean refrigerant circuit

(flush with refrigerant R134a

⇒ page 100 or blow out with

compressed air and nitrogen

⇒ page 95 ) (not always nec‐

essary, refer to notes).

♦ Air conditioner compressor regulating – Check operation of -N280- ,

valve - N280- defective

remove -N280- if applicable

and check for contamination

⇒ page 285 .

♦ Expansion valve or air conditioner

compressor defective.

– Renew expansion valve and

receiver.

♦ Air conditioner compressor defective

– Re-charge refrigerant circuit.

– Repeat test if operation is not

OK:

– Renew air conditioner com‐

pressor.

– Re-charge refrigerant circuit.

– Repeat test.

8. Checking pressures

227

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

Air conditioner with refrigerant R134a - Edition 11.2018

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.

♦ If the problem is with -N280- (the regulating valve is not actu‐

ated but the air conditioner compressor operates neverthe‐

less), the refrigerant circuit does not have to be cleaned (by

flushing with refrigerant R134a ⇒ page 100 or blowing out with

compressed air and nitrogen ⇒ page 95 ). In this case it is

sufficient to renew the air conditioner compressor (observe

quantity of refrigerant oil in compressor).

♦ If the expansion valve is defective (permanently closed or

does not open sufficiently), -N280- is actuated to maximum

output and the low pressure drops to the value in the graph or

below (the air conditioner compressor draws off refrigerant

from the low-pressure end). As refrigerant cannot however

flow via expansion valve, cooling output is not attained and

high pressure may either not increase or only slightly due to

the absence of energy conversion.

♦ Check the measured values of the evaporator output temper‐

ature sender - G263- and actuation of -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 conditioning; Rep.

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

ual).

228

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

Possible deviation from speci‐

fication

Possible causes of fault

Fault elimination

•

High pressure normal or too ♦ Actuation of air conditioner compres‐ – Check activation of -N280- ⇒

high

sor regulating valve - N280- not OK

Heating, air conditioning;

Rep. gr. 87 ; Refrigerant cir‐

cuit (vehicle-specific Work‐

shop Manual).

Low pressure too high (see ♦ Too much refrigerant in circuit

graph)

♦ Expansion valve defective

Noise from air conditioner

– Extract refrigerant from re‐

frigerant circuit.

♦ Air conditioner compressor defective

compressor (particularly af‐

ter being switched on)

•

The quantity of refrigerant

extracted corresponds

roughly to the actual capaci‐

ty.

•

Required cooling output is

attained.

– Renew expansion valve and

receiver.

– Re-charge refrigerant circuit.

– Repeat test if operation is not

OK:

– Renew air conditioner com‐

pressor.

•

If quantity of refrigerant ex‐

tracted is significantly great‐

er than specified capacity:

– Re-charge refrigerant circuit.

– Repeat test.

Note

♦ This fault may also be caused by too much refrigerant oil in

the circuit. Overfilling with refrigerant oil may occur if, for ex‐

ample, the air conditioner compressor has been renewed

without adjusting the quantity of refrigerant oil.

♦ If the expansion valve is defective (permanently closed or

does not open sufficiently), -N280- is actuated to maximum

output and the low pressure drops to the value in the graph or

below (the air conditioner compressor draws off refrigerant

from the low-pressure end). However, as refrigerant cannot

flow via the expansion valve, the cooling output is not attained

and the high pressure may also not increase or only increase

slightly since there is no energy exchange ⇒ 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 ; Refrigerant circuit (ve‐

hicle-specific Workshop Manual).

8. Checking pressures

229

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Checking pressures -> Checking pressures - vehicles with expansion valve, receiver and air conditioner compressor regulating valve N280 (with externally regulated air conditioner compressor) for Your Audi A2 SUV 1999-2005

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