Specified Values For The Refrigerant Circuit Pressures

WARNING: This page is about a different car, the 2023 Audi SQ8, 2023 Audi RS Q8, and 2023 Audi Q8. However, it is still accessible from the selected car via links, so may be relevant.

High-pressure side:

Increasing from initial pressure (when connecting the pressure gauges) to a maximum of 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 -

High Pressure in Bar

B -

Low Pressure in Bar

C -

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 The requested cooling output is not attained.	Not enough refrigerant in circuit or expansion valve malfunctioning.	-- Extract refrigerant from the refrigerant circuit. If the quantity of refrigerant extracted roughly corresponds to specified capacity: -- Replace the expansion valve.-- Charge the refrigerant circuit.-- Repeat the test.
High pressure normal Low pressure in line with value in graph, The requested cooling output is not attained.		If the quantity of refrigerant extracted is substantially less than specified capacity: -- Localize the leak with leak detector and eliminate.-- Charge the refrigerant circuit.-- Repeat the test.

NOTE:

If no malfunction can be found and air conditioner operation is not OK when test is repeated, clean 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 ).

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 does not activate (the A/C clutch). 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).
	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 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.	Constriction or obstruction in refrigerant circuit. Expansion valve malfunctioning.	-- Run a hand over refrigerant circuit to check for differences in temperature. Refer to SYSTEM OVERVIEW - REFRIGERANT CIRCUIT (vehicle-specific service information). 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 the refrigerant circuit: flush with refrigerant R134a (refer to Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ), or blow through with compressed air and nitrogen (refer to Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ), and replace the expansion valve if necessary. If no malfunction can be determined. -- Clean 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 ), and replace expansion valve if necessary.-- Repeat the test.

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.

Constriction or obstruction in refrigerant circuit.
Expansion valve malfunctioning.

-- Run a hand over refrigerant circuit to check for differences in temperature. Refer to SYSTEM OVERVIEW - REFRIGERANT CIRCUIT (vehicle-specific service information).

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 the refrigerant circuit: flush with refrigerant R134a (refer to Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ), or blow through with compressed air and nitrogen (refer to Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ), and replace the expansion valve if necessary.

If no malfunction can be determined.

-- Clean 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 ), and replace expansion valve if necessary.-- Repeat the test.

NOTE:

If the operation is not OK after cleaning refrigerant circuit by flushing with R134a (refer to Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ), or blowing through using compressed air and nitrogen (refer to Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ), expansion valve must be replaced.

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 and low pressure drops to value in graph or below Required cooling output is no longer attained.	Expansion valve malfunctioning. Moisture in refrigerant circuit	-- Replace the receiver/dryer (with dryer) and evacuate the refrigerant circuit for a minimum of three hours (see notes).-- Examine the expansion valve for dirt or corrosion; replace if necessary.-- 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 ).
High and low pressure normal at first. After lengthy operating period, the low pressure drops excessively (evaporator ices up).

NOTE:

It is not initially necessary to clean the refrigerant circuit by flushing with refrigerant R134a (refer to Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ), or blowing 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.

Possible deviation from specification	Possible cause of fault	Corrective action
High pressure normal or too high, Low pressure too high (see graph), The requested cooling output is not attained. A/C compressor noise (particularly after switch-on).	Too much refrigerant in the circuit. Expansion valve or A/C compressor faulty.	-- Extract refrigerant from the refrigerant circuit. If quantity of refrigerant extracted roughly corresponds to specified capacity: -- Replace the expansion valve.-- Charge the refrigerant circuit.-- Repeat the test. If the 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),
The requested cooling output is not attained.
A/C compressor noise (particularly after switch-on).

Too much refrigerant in the circuit.
Expansion valve or A/C compressor faulty.

-- Extract refrigerant from the refrigerant circuit.

If quantity of refrigerant extracted roughly corresponds to specified capacity:

-- Replace the expansion valve.-- Charge the refrigerant circuit.-- Repeat the test.

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

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

NOTE:

If air conditioner operation is not OK when test is repeated, install the old expansion valve, clean refrigerant circuit by flushing using 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 ). Then replace the A/C compressor and receiver/dryer.

Possible deviation from specification	Possible cause of fault	Corrective action
High pressure only increases slightly above pressure with engine stopped Low pressure drops only slightly The requested cooling output is not attained.	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 REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ).-- Replace the A/C compressor and receiver/dryer.

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.	Expansion valve or A/C compressor faulty.	-- Replace the expansion valve.-- Charge the refrigerant circuit.-- Repeat the test.

NOTE:

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

Possible deviation from specification	Possible cause of fault	Corrective action
High and low pressure normal, The requested cooling output is not attained.	Too much refrigerant oil in the circuit.	-- Discharge the 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 ).
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 receiver/dryer 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 using 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 .