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Home >> Audi >> 2020 >> SQ8 Premium Plus >> Repair and Diagnosis >> External Pages >> Different car >> Section 212 (Air Conditioning (Refrigerant R134A Servicing) (Pressures - Refrigerant Oils)) >> 87 Air Conditioning >> Pressures, Checking >> PRESSURES, CHECKING, VEHICLES WITH EXPANSION VALVE, RECEIVER/DRYER AND A/C Compressor Regulator Valve -N280-, EXTERNALLY REGULATED COMPRESSOR >> Specified Values For The Refrigerant Circuit Pressures

Specified Values For The Refrigerant Circuit Pressures

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High-Pressure Side:

Increasing from initial pressure (when connecting the pressure gauges) to a maximum of 20 bar (290.08 psi).

Low Pressure:

Decreasing from initial pressure (when connecting pressure gauges) to the value in the graph.

Fig 1: Identifying Permissible Tolerance Range Graph
GWWA87-10582Courtesy of AUDI

A -  Low Pressure (Measured at Service Connection) in Bar Absolute Pressure.

B -  Control current for A/C Compressor Regulator Valve -N280- in amps.

C -  Permissible tolerance range (applicable to compressor capacity utilization of 10 to 90 %)

NOTE:

If high cooling output is needed (for example, the outside temperature is very high, the blower speed it set on high but the engine speeds are low), then the A/C compressor will not bring the pressure on the low pressure side to the value specified in the diagram -C- (for example, for a certain time after turning on the A/C). The A/C compressor is actuated with maximum specified control current, however delivery volume is no longer sufficient at this engine speed to reduce pressure on low-pressure side to value in graph. To check the A/C compressor control under these conditions, for example, the fresh air blower is activated only with approximately 40% of the maximum voltage and check the pressures at a lower fresh air blower speed. Use the Vehicle Diagnostic Tester ("OBD" function or "Guided Fault Finding" for the A/C system) and refer to COOLING OUTPUT, CHECKING or Refrigerant Circuit (vehicle-specific repair information).

Under unfavorable conditions (very high ambient temperatures, high humidity), pressure on high-pressure side may increase to maximum 29 bar (420.61 psi).

The control current -B- is displayed in the measured value block of Front A/C Display Control Head -E87- or the Climatronic Control Module -J255-.

The high pressure measured by the High Pressure Sensor -G65- (or the A/C Pressure/Temperature Sensor -G395- or the Refrigerant Circuit Pressure Sensor -G805-) is displayed as a measured value (by the Front A/C Display Control Head Front A/C Display Control Head -E87-, the A/C Control Module -J301- or the Climatronic Control Module -J255- display control head).

Low pressure settles depending on the control current for A/C Compressor Regulator Valve -N280- and control characteristic of expansion valve within compressor output range in tolerance range.

Under unfavorable conditions (very high ambient temperatures, high humidity), compressor output may not always be sufficient to attain the specified value.

If compressor capacity utilization is greater than 90 %, pressure on low-pressure side may be in excess of tolerance range "C" shown in graph (compressor output no longer sufficient).

The specified operating current for the A/C Compressor Regulator Valve -N280- must be greater than 0.3 A in order to ensure reliable regulator valve actuation.

In "maximum cooling output" setting, control current for A/C Compressor Regulator Valve -N280- is regulated to approximately 0.65 A (up to 0.85 A). This measured value is vehicle-specific and displayed in the measured value block.

At absolute pressure, 0 bar (0 psi) corresponds to absolute vacuum. Normal ambient pressure corresponds to 1 bar (14.5 psi) absolute pressure. On the scales of most pressure gauges, 0 bar (0 psi) corresponds to an absolute pressure of one bar (can be seen from -1 bar (-14.5 psi) mark below 0). Use the Vehicle Diagnostic Tester ("OBD" or "Guided Fault Finding" for the A/C System) and refer to COOLING OUTPUT, CHECKING or Refrigerant Circuit (vehicle-specific repair information).

Possible deviation from specification Possible cause of fault Corrective action
  • High pressure remains constant or increases only slightly (above pressure with engine stopped),
  • Low pressure quickly drops to value in graph or below.
  • The requested cooling output is not attained.
  • Activation of A/C Compressor Regulator Valve -N280- malfunctioning.
  • Not enough refrigerant in refrigerant circuit.
  • Expansion valve malfunctioning.
 -- Check the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- activation. Refer to Refrigerant Circuit (vehicle-specific repair information).-- Extract refrigerant from the refrigerant circuit.
  • If quantity of refrigerant extracted is substantially less than specified capacity:
  • High pressure normal
  • Low pressure in line with value in graph,
  • The requested cooling output is not attained.
   -- Localize the leak with leak detector and eliminate.-- Charge the refrigerant circuit.-- Repeat the test.
  • High pressure normal
  • Low pressure too low (see graph)
  • The requested cooling output is not attained.
  
  • If quantity of refrigerant extracted roughly corresponds to specified capacity:
-- Replace the expansion valve.-- Charge the refrigerant circuit.-- Repeat the test.
NOTE:

If no error is detected with this complaint, clean the refrigerant circuit (by flushing with refrigerant R134a, Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or clean using compressed air and nitrogen, Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ).

Check the measured values from the Evaporator Vent Temperature Sensor -G263- and the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280-. If the measured value of the Evaporator Vent Temperature Sensor -G263- is incorrect, the evaporator may ice up or cooling output is not attained.

If air conditioner operation is not OK when test is repeated after replacing expansion valve, install old expansion valve, clean refrigerant circuit by flushing with refrigerant R134a (Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ), or blowing through with compressed air and nitrogen (Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ). Then replace the A/C compressor and receiver/dryer.

With this malfunction, evaporator may ice up although the quantity of refrigerant in circuit is OK.

If the expansion valve is faulty (constantly closed or does not open far enough), the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- is actuated to maximum output and the low pressure drops to value in graph or below (the A/C compressor draws off refrigerant from low-pressure side). Since the refrigerant cannot flow via the expansion valve, cooling output is not attained. High pressure may also not increase or only increase slightly due to the absence of energy. Use the Vehicle Diagnostic Tester ("OBD" or "Guided Fault Finding" for the A/C System) and refer to COOLING OUTPUT, CHECKING or Refrigerant Circuit (vehicle-specific repair information).

Possible deviation from specification Possible cause of fault Corrective action
  • High pressure does not increase or only increases slightly above pressure with engine stopped.
  • Low pressure does not drop or drops only slightly.
  • The requested cooling output is not attained.
  • The A/C compressor is not activated (A/C Compressor Regulator Valve -N280-)
  • The A/C compressor is not being driven.
 -- Check and service the A/C compressor activation and motor. Refer to A/C Compressor (vehicle-specific repair information).
 
  • A/C Compressor Regulator Valve -N280- faulty.
 -- Check the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- function. If necessary, remove the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- and check for dirt. Refer to A/C Compressor Regulator Valve -N280-, REMOVING, INSTALLING AND REPLACING .
 
  • Constriction or obstruction in refrigerant circuit (for example, inside the refrigerant line between the service connection "low pressure side" and the A/C compressor).
 -- Clean the refrigerant circuit by flushing with refrigerant R134a (Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ) or blow through using compressed air and nitrogen (Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ).-- Replace the hose or pipe if kinked or constricted.
 
  • A/C compressor faulty.
 -- Replace the A/C compressor.
NOTE:

Make sure that the A/C compressor (the A/C compressor shaft) is actually being driven by the belt pulley/drive unit for this complaint. Refer to A/C Compressor (vehicle-specific repair information).

From MY 2012, certain engines and A/C compressor versions are being introduced that, in addition to the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280-, an A/C Clutch -N25- is being attached to the belt pulley. Make sure that the A/C Clutch A/C Clutch -N25- is actually being actuated and the A/C compressor (A/C compressor shaft) is being driven by the belt pulley. Refer to A/C Compressor (vehicle-specific repair information) and to the appropriate Electronic Parts Information.

Possible deviation from specification Possible cause of fault Corrective action
  • High pressure increases above specification
  • Low pressure quickly drops to value in graph,
  • Required cooling output is not attained.
  • Activation of A/C Compressor Regulator Valve -N280- malfunctioning.
  • Constriction or obstruction in refrigerant circuit.
  • Expansion valve malfunctioning.
 -- Check the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- activation. Refer to Refrigerant Circuit (vehicle-specific repair information).-- Run hand over refrigerant circuit to check for differences in temperature.
  • If difference in temperature is found at one component:
-- Replace the hose or pipe if kinked or constricted.-- In the event of an obstruction, clean refrigerant circuit by flushing with refrigerant R134a (Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ), or blowing through with compressed air and nitrogen (Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ).-- Charge the refrigerant circuit.-- Repeat the test.
  • If no error can be found:
-- Clean the refrigerant circuit by flushing with refrigerant R134a (Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ) or blow through using compressed air and nitrogen (Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ).-- Charge the refrigerant circuit.-- Repeat the test if the function is not OK:-- Replace expansion valve and receiver/dryer
NOTE:

If the function of the A/C system is not OK when the test is repeated, replace the expansion valve and receiver/dryer.

With this malfunction, evaporator may ice up although the quantity of refrigerant in circuit is OK.

If the expansion valve is faulty (constantly closed or does not open far enough), the A/C Compressor Regulator Valve -N280- is actuated to maximum output and low pressure drops to value in graph or below (the A/C compressor draws off refrigerant from low-pressure side). Since the refrigerant cannot flow via the expansion valve, the cooling output is not attained. High pressure may also not increase or only increase slightly due to the absence of energy. Use the Vehicle Diagnostic Tester ("OBD" or "Guided Fault Finding" for the A/C System) and refer to COOLING OUTPUT, CHECKING or Refrigerant Circuit (vehicle-specific repair information).

If there is too much refrigerant oil in the circuit, the compressor must be drained and the receiver/dryer must be replaced. After cleaning the refrigerant circuit by flushing with refrigerant R134a (Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ), or blowing through with compressed air and nitrogen (Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ), fill the circuit with the correct quantity of refrigerant oil. Refer to APPROVED REFRIGERANT OILS AND REFRIGERANT OIL CAPACITIES .

Possible deviation from specification Possible cause of fault Corrective action
  • High and low pressure normal at first after some time,
  • High pressure increases above specification,
  • Low pressure quickly drops to value in graph or below,
  • Required cooling output is no longer attained.
  • Activation of A/C Compressor Regulator Valve -N280- malfunctioning.
  • Moisture in refrigerant circuit
 -- Check the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- activation. Refer to Refrigerant Circuit (vehicle-specific repair information).-- Clean the refrigerant circuit by flushing with refrigerant R134a (Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ) or blow through using compressed air and nitrogen (Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ).
  • High and low pressure normal at first,
  • After lengthy driving time, low pressure drops excessively (evaporator ices up).
   -- Replace the receiver/dryer with dryer.-- Evacuate the refrigerant circuit for at least three hours.-- Charge the refrigerant circuit.-- Repeat the test.
 
  • A/C Compressor Regulator Valve -N280- faulty
 -- Check the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- function. If necessary, remove the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- and check for dirt. Refer to A/C Compressor Regulator Valve -N280-, REMOVING, INSTALLING AND REPLACING .
NOTE:

It is not initially necessary to clean the refrigerant circuit by flushing using refrigerant R134a (Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ) or blow through using compressed air and nitrogen (Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ) when this problem occurs since normally, there is only a small quantity of moisture in the system which can be removed by lengthy evacuation.

If a problem involving moisture in refrigerant circuit only occurs after a lengthy operating period or only infrequently (low pressure drops below specification and evaporator ices up), it is sufficient to replace the dryer installed in receiver/dryer (adjust quantity of refrigerant oil). Refrigerant circuit is then to be evacuated for at least three hours.

With this malfunction, evaporator may ice up although the quantity of refrigerant in circuit is OK.

A malfunction on the Evaporator Vent Temperature Sensor -G263- can also cause icing-up of refrigerant circuit. With this complaint, also pay attention to the measured value for the Evaporator Vent Temperature Sensor -G263-. Use the Vehicle Diagnostic Tester ("OBD" or "Guided Fault Finding" for the A/C System) and refer to COOLING OUTPUT, CHECKING or Refrigerant Circuit (vehicle-specific repair information).

Possible deviation from specification Possible cause of fault Corrective action
  • High pressure normal
  • Low pressure too low (see graph),
  • The required cooling performance is obtained.
  • Activation of A/C Compressor Regulator Valve -N280- malfunctioning.
 -- Check the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- activation. Refer to Refrigerant Circuit (vehicle-specific repair information).-- Clean the refrigerant circuit by flushing with refrigerant R134a (Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ); or blowing through with compressed air and nitrogen (Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ) (not always necessary, see notes).
 
  • A/C Compressor Regulator Valve -N280- faulty
 -- Check the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- function. If necessary, remove the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- and check for dirt. Refer to A/C Compressor Regulator Valve -N280-, REMOVING, INSTALLING AND REPLACING .
 
  • Expansion valve or A/C compressor faulty.
  • A/C compressor faulty.
 -- Replace expansion valve and receiver/dryer-- Charge the refrigerant circuit.-- Repeat the test if the function is not OK:-- Replace the A/C compressor.-- Charge the refrigerant circuit.-- Repeat the test.
NOTE:

For the malfunction "high pressure normal, low pressure too low" With this malfunction, evaporator may ice up, although quantity of refrigerant in circuit is OK.

If the fault is with the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- (regulator valve is not actuated but A/C compressor operates nevertheless), it is not necessary to clean the refrigerant circuit by flushing with refrigerant R134a (Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ) or blowing through using compressed air and nitrogen (Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ). In this case, it is sufficient to replace the A/C compressor (observe quantity of refrigerant oil in A/C compressor).

If the expansion valve is faulty (constantly closed or does not open far enough), the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- is actuated to maximum output and low pressure drops to value in graph or below (A/C compressor draws off refrigerant from low-pressure side). As however refrigerant cannot flow via the expansion valve, the cooling output is not attained and high pressure may also not increase or only increase slightly due to the absence of energy conversion.

Check the measured values of the Evaporator Vent Temperature Sensor -G263- and the activation of the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280-. If the measured value from the Evaporator Vent Temperature Sensor -G263- is incorrect, the evaporator may ice up or cooling output is not reached. Use the Vehicle Diagnostic Tester ("OBD" or "Guided Fault Finding " for the A/C System) and refer to COOLING OUTPUT, CHECKING or Refrigerant Circuit (vehicle-specific repair information).

Possible deviation from specification Possible cause of fault Corrective action
  • High pressure normal or too high,
  • Low pressure too high (see graph),
  • A/C compressor noise (particularly after switch-on),
  • The required cooling performance is obtained.
  • Activation of A/C Compressor Regulator Valve -N280- malfunctioning.
  • Too much refrigerant in the circuit.
  • Expansion valve malfunctioning.
  • A/C compressor faulty.
 -- Check the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- activation. Refer to Refrigerant Circuit (vehicle-specific repair information).-- Extract refrigerant from the refrigerant circuit.
  • If quantity of refrigerant extracted roughly corresponds to specified capacity:
-- Replace expansion valve and receiver/dryer-- Charge the refrigerant circuit.-- Repeat the test if the function is not OK:-- Replacing the A/C compressor.
  • If quantity of refrigerant extracted is substantially greater than specified capacity:
-- Charge the refrigerant circuit.-- Repeat the test.
NOTE:

This fault may also be caused by too much refrigerant oil in the circuit. Overfilling with refrigerant oil can occur if, for example, the compressor has been replaced without adjusting the quantity of refrigerant oil.

If the expansion valve is faulty (constantly closed or does not open far enough), the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- is actuated to maximum output and the low pressure drops to value in graph or below (the A/C compressor draws off refrigerant from low-pressure side). Since the refrigerant cannot flow via the expansion valve, the cooling output is not attained. High pressure may also not increase or only increase slightly due to the absence of energy. Use the Vehicle Diagnostic Tester ("OBD" or "Guided Fault Finding" for the A/C System) and refer to COOLING OUTPUT, CHECKING or Refrigerant Circuit (vehicle-specific repair information).

Possible deviation from specification Possible cause of fault Corrective action
  • High and low pressure normal,
  • The required cooling performance is obtained.
  • Activation of A/C Compressor Regulator Valve -N280- malfunctioning.
  • Too much refrigerant in the circuit.
  • Expansion valve malfunctioning.
 -- Check the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- activation. Refer to Refrigerant Circuit (vehicle-specific repair information).-- Discharge the refrigerant circuit.-- Clean the refrigerant circuit by flushing with refrigerant R134a (Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ) or blow through using compressed air and nitrogen (Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ).
  • High and low pressure normal,
  • A/C compressor noise (particularly after switch-on),
  • The required cooling performance is obtained.
   -- Fill in correct quantity of refrigerant oil into circuit (see note).-- Charge the refrigerant circuit.-- Repeat the test if the function is not OK:-- Replace the expansion valve.-- Charge the refrigerant circuit.-- Repeat the test.
NOTE:

Overfilling with refrigerant oil can occur if, for example, the compressor has been replaced without adjusting the quantity of refrigerant oil.

If the expansion valve is malfunctioning (permanently open), evaporator temperature is no longer regulated such that only refrigerant in gaseous state exits from the evaporator. Under certain usage conditions, liquid droplets may then be drawn in by the compressor and cause noise (liquid cannot be compressed).

If there is too much refrigerant oil in the circuit, the compressor must be drained and the receiver/dryer must be replaced. After cleaning the refrigerant circuit by flushing with refrigerant R134a (Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ), or blowing through with compressed air and nitrogen (Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ), fill the circuit with the correct quantity of refrigerant oil. Refer to APPROVED REFRIGERANT OILS AND REFRIGERANT OIL CAPACITIES .

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