Specified Values For The Refrigerant Circuit Pressures

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High-pressure side:

Increasing from initial pressure (when connecting pressure gauges) to 20 bar (290.08 psi).

Low-pressure side:

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

Fig 1: Identifying Permissible Tolerance Range Graph

Courtesy of AUDI OF AMERICA, LLC

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

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 the appropriate Cooling Output Checking procedure in REPAIR INFORMATION or Refrigerant Circuit (vehicle-specific service information).

Under unfavorable conditions (very high ambient temperatures, high humidity), pressure on high-pressure side may increase up 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- display control head.

The refrigerant circuit pressure measured by the High Pressure Sensor -G65- or the A/C Pressure/Temperature Sensor -G395- is displayed in the measured value block for the Front A/C Display Control Head Front A/C Display Control Head -E87- or the Climatronic Control Module -J255- display control head. Use the Vehicle Diagnostic Tester ("OBD" function or "Guided Fault Finding" for the A/C system) and refer to Refrigerant Circuit (vehicle-specific service information).

Low pressure settles as a function of control current for A/C Compressor Regulator Valve -N280- 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 regulator valve must be greater than 0.3 A in order to ensure reliable valve activation.

At absolute pressure, "0 bar (0 psi)" corresponds to absolute vacuum. Normal ambient pressure corresponds to 1 bar (14.5 psi) absolute pressure. 0 bar (0 psi) pressure corresponds to an absolute pressure of one bar on most pressure gauges (indicated by "-1 bar (-14.5 psi)" below "0").

At the "maximum cooling output" setting, the control current is regulated to approximately 0.65 (vehicle-specific up to 0.85A, displayed in measured value block). Use the Vehicle Diagnostic Tester ("OBD" or "Guided Fault Finding" for the A/C System) and the appropriate Cooling Output Checking procedure in REPAIR INFORMATION or Component Location Overview - A/C System (vehicle-specific service 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.	-- Check the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- activation. Refer to Refrigerant Circuit (vehicle-specific service information).-- Localize the leak with leak detector and eliminate.-- Charge the refrigerant circuit.
High pressure normal Low pressure too low (see graph), The requested cooling output is not attained.

NOTE:

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

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 service information).-- Check the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- activation and function.
	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 Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ) or blow through using compressed air and nitrogen (refer to Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ).-- Replace the hose or pipe if kinked or constricted.
	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 .
	A/C compressor faulty.	-- Replace the A/C compressor.

Possible deviation from specification	Possible cause of fault	Corrective action
High pressure increases above specification 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. Constriction or obstruction in refrigerant circuit.	-- Check the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- activation. Refer to Refrigerant Circuit (vehicle-specific service 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, flush the refrigerant circuit with compressed air and nitrogen. If no error can be found: -- Clean the refrigerant circuit by flushing with refrigerant R134a (refer to Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ) or blow through using compressed air and nitrogen (refer to Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ).

Possible deviation from specification

Possible cause of fault

Corrective action

High pressure increases above specification
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.
Constriction or obstruction in refrigerant circuit.

-- Check the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- activation. Refer to Refrigerant Circuit (vehicle-specific service 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, flush the refrigerant circuit with compressed air and nitrogen.

If no error can be found:

-- Clean the refrigerant circuit by flushing with refrigerant R134a (refer to Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ) or blow through using compressed air and nitrogen (refer to Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ).

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.	-- Check the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- activation. Refer to Refrigerant Circuit (vehicle-specific service information).-- Replace the reservoir (with dryer) and evacuate the refrigerant circuit for a minimum of three hours (see note).
High and low pressure normal at first. After lengthy operating period, the low pressure drops excessively (evaporator ices up).	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 .
	Moisture in refrigerant circuit	-- Clean the refrigerant circuit by flushing with refrigerant R134a (refer to Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ) or blow through using compressed air and nitrogen (refer to Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ).

NOTE:

It is not initially necessary to clean the refrigerant circuit by flushing using refrigerant R134a (refer to Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ) or blow through using compressed air and nitrogen (refer to 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 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 (adjust quantity of refrigerant oil). Refrigerant circuit is then to be evacuated for at least three hours.

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 appropriate Cooling Output Checking procedure in REPAIR INFORMATION or Refrigerant Circuit (vehicle-specific service 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. A/C Compressor Regulator Valve -N280- faulty	-- Check the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- activation. Refer to Refrigerant Circuit (vehicle-specific service information).-- 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 .
	A/C compressor faulty.	-- Clean the refrigerant circuit by flushing with refrigerant R134a (refer to Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ) or blow through using compressed air and nitrogen (refer to Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ).-- Replace the A/C compressor.

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. Check the measured values from the Evaporator Vent Temperature Sensor -G263- and the activation of the 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 appropriate Cooling Output Checking procedure in REPAIR INFORMATION or Refrigerant Circuit (vehicle-specific service 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 requested cooling output is not attained.	Activation of A/C Compressor Regulator Valve -N280- malfunctioning. Too much refrigerant in the circuit.	-- Check the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- activation. Refer to Refrigerant Circuit (vehicle-specific service information).-- Extract refrigerant from the refrigerant circuit. If quantity of refrigerant extracted roughly corresponds to specified capacity: -- Replacing the A/C compressor. If the quantity of refrigerant extracted is substantially greater than specified capacity: -- Charge the refrigerant circuit.-- Repeat the test.
High and low pressure normal, The requested cooling output is not attained.	Activation of A/C Compressor Regulator Valve -N280- malfunctioning. Too much refrigerant oil in the circuit.	-- Check the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- activation.-- Discharge the refrigerant circuit.
High and low pressure normal. A/C compressor noise (particularly after switch-on). The required cooling performance is obtained.		-- Clean the refrigerant circuit by flushing with refrigerant R134a (refer to Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ) or blow through using compressed air and nitrogen (refer to Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ).

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 requested cooling output is not attained.

Activation of A/C Compressor Regulator Valve -N280- malfunctioning.
Too much refrigerant in the circuit.

-- Check the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- activation. Refer to Refrigerant Circuit (vehicle-specific service information).-- Extract refrigerant from the refrigerant circuit.

If quantity of refrigerant extracted roughly corresponds to specified capacity:

-- Replacing the A/C compressor.

If the quantity of refrigerant extracted is substantially greater than specified capacity:

-- Charge the refrigerant circuit.-- Repeat the test.

High and low pressure normal,
The requested cooling output is not attained.

Activation of A/C Compressor Regulator Valve -N280- malfunctioning.
Too much refrigerant oil in the circuit.

-- Check the A/C Compressor Regulator Valve A/C Compressor Regulator Valve -N280- activation.-- Discharge the refrigerant circuit.

High and low pressure normal.
A/C compressor noise (particularly after switch-on).
The required cooling performance is obtained.

NOTE:

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

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