Specified Values For The Refrigerant Circuit Pressures

High-Pressure Side:

Increasing from initial pressure (when connecting the pressure gauges) to a maximum of 20 bar (290 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 - High pressure (measured at service connection) in bar (psi)

B - Low pressure (measured at connection with valve at compressor or accumulator) in bar

C - Permissible tolerance range

D - Low pressure (measured at connection with valve for low-pressure switch or at service connection) in bar (psi)

E - Permissible tolerance range

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 Required cooling output is not attained	Not enough refrigerant in refrigerant circuit	-- Localize leak with leak detector and eliminate.-- Charge the refrigerant circuit.
High pressure normal Low pressure in line with value in graph 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 with this malfunction, clean the refrigerant circuit (flush using refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blow through using compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING 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. Required cooling output is not attained	The A/C compressor does not activate (the A/C clutch). The A/C compressor is not being driven.	-- Check and service the A/C compressor activation and drive. Refer to A/C Compressor .
	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 (flush with refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blow through with compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN ).-- Replace the hose or line if kinked or constricted.
	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 Required cooling output is not attained	Constriction or obstruction in refrigerant circuit	-- Run hand over refrigerant circuit to check for differences in temperature. Refer to Refrigerant Circuit . If difference in temperature is found at one component: -- Replace the hose or line if kinked or constricted.-- In the event of an obstruction, clean refrigerant circuit (flush with refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blow through with compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN ). If no malfunction can be found: -- Clean the refrigerant circuit (flush with refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blow through with compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN ).
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.	Moisture in refrigerant circuit	-- Check the reservoir (with dryer) and restrictor and replace if necessary. Then evacuate the refrigerant circuit for a minimum of three hours (see note).-- Clean the refrigerant circuit (flush with refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blow through with compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN ).
High and low pressure normal at first After lengthy operating period, the low pressure drops excessively (evaporator ices up).

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
Required cooling output is not attained

Constriction or obstruction in refrigerant circuit

-- Run hand over refrigerant circuit to check for differences in temperature. Refer to Refrigerant Circuit .

If difference in temperature is found at one component:

-- Replace the hose or line if kinked or constricted.-- In the event of an obstruction, clean refrigerant circuit (flush with refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blow through with compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN ).

If no malfunction can be found:

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

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.

Moisture in refrigerant circuit

-- Check the reservoir (with dryer) and restrictor and replace if necessary. Then evacuate the refrigerant circuit for a minimum of three hours (see note).-- Clean the refrigerant circuit (flush with refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blow through with compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN ).

High and low pressure normal at first
After lengthy operating period, the low pressure drops excessively (evaporator ices up).

NOTE:

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.

It is not initially necessary to clean the refrigerant circuit (flush using refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A . Or blow through using compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING 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.

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.	A/C compressor faulty.	-- Clean the refrigerant circuit (flush with refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blow through with compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN ).-- Replace the A/C compressor.

NOTE:

For the malfunction "high pressure normal, low pressure too low", note the following: This fault may cause the evaporator to ice up or the A/C Refrigerant Low Pressure Switch -F73- to shut off the compressor although the amount of refrigerant in the circuit is OK.

On the Audi 100, Audi A6 (through MY1997) and Audi V8, this fault may result in compressor being shut off by the control head (if the temperature at fresh-air blower drops below -3 °C (27 °F)). Refer to Refrigerant Circuit or Component Location Overview - A/C System .

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) Required cooling output is not attained	Too much refrigerant in the circuit.	-- Extract refrigerant from the refrigerant circuit If quantity of refrigerant extracted roughly corresponds to specified capacity: -- Replace the A/C compressor. If quantity of refrigerant extracted is substantially greater than specified capacity: -- Charge the refrigerant circuit.-- Repeat the test.

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)
Required cooling output is not attained

Too much refrigerant in the circuit.

-- Extract refrigerant from the refrigerant circuit

If quantity of refrigerant extracted roughly corresponds to specified capacity:

-- Replace the A/C compressor.

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

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

Possible Deviation from Specification	Possible Cause of Fault	Corrective Action
High and low pressure normal Required cooling output is not attained	Too much refrigerant oil in the circuit.	-- Discharge the refrigerant circuit.-- Clean the refrigerant circuit (flush with refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blow through with compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN ).
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 compressor must be drained and the accumulator must be replaced. After cleaning the refrigerant circuit (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, FLUSHING WITH COMPRESSED AIR AND NITROGEN ), the correct quantity of refrigerant oil is filled into the circuit. Refer to REFRIGERANT R134A CAPACITIES, REFRIGERANT OIL AND APPROVED REFRIGERANT OILS .