Pressure Checking, Vehicles with Restrictor, Reservoir and A/C Compressor Regulator Valve with Externally Regulated Compressor

WARNING: This page does not describe the selected car, but rather 17 other vehicles, including the 2009 Audi S4, 2009 Audi A4, 2008 Audi S4, 2008 Audi RS 4, and 2008 Audi A4. However, it is still accessible from the selected car via links, so may be relevant.

NOTE:

Connecting A/C service station → A/C Service Station, Connecting
Observe test conditions → Refrigerant Circuit, Checking Pressures with A/C Service Station .
Set engine speed to 2000 rpm.
Observe pressure display (e.g. pressure gauge) of A/C service station.

NOTE:

Switching pressures for actuation of A/C Compressor Regulator Valve N280 and Coolant Fans V7 are vehicle-specific.
Pressures must be measured at service connections; component locations of these connections are vehicle-specific → 87 - Air conditioning .

Specifications

High-pressure side:

Increasing from initial pressure (on connection of pressure gauges) to 20 bar

Low-pressure side:

Fig 1: Permissible Tolerance Range Graph

Courtesy of VOLKSWAGEN UNITED STATES, INC.

Decreasing from initial pressure (on connecting pressure gauges) to value in graph

A - Low pressure (measured at service connection) in bar absolute

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

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

NOTE:

Given high ambient temperature and a low engine speed, compressor may for example no longer be able to adjust pressure on low-pressure side to value given in graph. 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 , air conditioner Guided Fault Finding function and → 87 - Air conditioning .

NOTE:

Under unfavorable conditions (very high ambient temperatures, high humidity), pressure on high-pressure side may increase to max. 29 bar.
Control current - B - is displayed in measured value block of A/C Control Head E87 or control head, Climatronic Control Module J255.
Pressure in refrigerant circuit measured by High Pressure Sensor G65 or A/C Pressure/temperature Sensor G395 is displayed in measured value block of A/C Control Head E87 or control head, Climatronic Control Module J255 and → 87 - Air conditioning .
Low pressure settles as a function of control current for A/C Compressor Regulator Valve N280 within compressor output range in tolerance band.
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 suffices).
The specified operating current for the regulator valve must be greater than 0.3 A in order to ensure reliable valve actuation.
At absolute pressure, "0 bar" corresponds to an absolute vacuum. Normal ambient pressure corresponds to "1 bar" absolute. On the scales of most pressure gauges, "0 bar" corresponds to an absolute pressure of 1 bar (can be seen from "-1 bar" mark below "0" ).
In "maximum cooling output" setting, control current is regulated to approx. 0.65 (vehicle-specific up to 0.85 A) (displayed in measured value block) , air conditioner Guided Fault Finding function and → 87 - Air conditioning .

Possible deviation from specification	Possible cause of trouble	Corrective action
High pressure remains constant or only increases slightly (above pressure with engine stopped) Low pressure quickly drops to value in graph or below Required cooling output is not attained	Problem with actuation of A/C Compressor Regulator Valve N280 Not enough refrigerant in circuit	Check actuation of A/C Compressor Regulator Valve N280 Localize leak using leak detector and eliminate Recharge refrigerant circuit
High pressure normal Low pressure too low (see 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 complaint, clean refrigerant circuit (flush using refrigerant R134a → Refrigerant Circuit, Flushing with Refrigerant R134a or blow through using compressed air and nitrogen → Refrigerant Circuit, Flushing with Compressed Air and Nitrogen ).

Possible deviation from specification	Possible cause of trouble	Corrective action
High pressure only increases slightly above pressure with engine stopped Low pressure only drops slightly Required cooling output is not attained	Problem with actuation of A/C Compressor Regulator Valve N280 Compressor malfunctioning	Check actuation of A/C Compressor Regulator Valve N280 Clean refrigerant circuit (flush with refrigerant R134a or blow through with compressed air and nitrogen ) Replace compressor
High pressure increases above specification Low pressure quickly drops to value in graph or below Required cooling output is not attained	Problem with actuation of A/C Compressor Regulator Valve N280 Constriction or obstruction in refrigerant circuit	Check actuation of A/C Compressor Regulator Valve N280 Run hand over refrigerant circuit to check for differences in temperature If difference in temperature is found at one component: Replace hose or pipe if kinked or constricted In the event of an obstruction, flush refrigerant circuit with compressed air and nitrogen If no fault is found: Clean refrigerant circuit (flush with refrigerant R134a or blow through with compressed air and nitrogen )

Possible deviation from specification	Possible cause of trouble	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	Problem with actuation of A/C Compressor Regulator Valve N280 Moisture in refrigerant circuit	Check actuation of A/C Compressor Regulator Valve N280 Replace reservoir (with dryer) and evacuate refrigerant circuit for at least 3 hours (see note) Clean refrigerant circuit (flush with refrigerant R134a or blow through with compressed air and nitrogen )
High and low pressure normal at first After lengthy operating period, low pressure drops excessively (evaporator ices up)

NOTE:

It is not initially necessary to clean the refrigerant circuit (flush using refrigerant R134a → Refrigerant Circuit, Flushing with Refrigerant R134a or blow through using compressed air and nitrogen → 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.
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 3 hours.
Problem with Evaporator Vent Temperature Sensor G263 can also cause icing-up of refrigerant circuit. If this problem is encountered, also pay attention to measured value of Evaporator Vent Temperature Sensor G263 , air conditioner Guided Fault Finding function and → 87 - Air conditioning .

Possible deviation from specification	Possible cause of trouble	Corrective action
High pressure normal Low pressure too low (see graph) Required cooling output attained	Problem with actuation of A/C Compressor Regulator Valve N280 Compressor malfunctioning	Check actuation of A/C Compressor Regulator Valve N280 Clean refrigerant circuit (flush with refrigerant R134a or blow through with compressed air and nitrogen ) Replace compressor

NOTE:

Pay attention to the following as regards fault "High pressure normal, low pressure too low" : This fault may lead to icing-up of evaporator although quantity of refrigerant in circuit is OK. Check measured values of Evaporator Vent Temperature Sensor G263 and actuation of A/C Compressor Regulator Valve N280. If measured value of Evaporator Vent Temperature Sensor G263 is incorrect, evaporator may ice up or cooling output is not attained , air conditioner Guided Fault Finding function and → 87 - Air conditioning .

Possible deviation from specification	Possible cause of trouble	Corrective action
High pressure normal or too high Low pressure too high (see graph) Compressor noise (particularly after switch-on) Required cooling output is not attained	Problem with actuation of A/C Compressor Regulator Valve N280 Too much refrigerant in circuit	Check actuation of A/C Compressor Regulator Valve N280 Extract refrigerant from refrigerant circuit If quantity of refrigerant extracted roughly corresponds to specified capacity: Replace compressor If quantity of refrigerant extracted is substantially greater than specified capacity: Recharge refrigerant circuit Repeat test
High and low pressure normal Required cooling output is not attained	Problem with actuation of A/C Compressor Regulator Valve N280 Too much refrigerant oil in circuit	Check actuation of A/C Compressor Regulator Valve N280 Discharge refrigerant circuit Clean refrigerant circuit (flush with refrigerant R134a or blow through with compressed air and nitrogen )
High and low pressure normal Compressor noise (particularly after switch-on) Required cooling output attained

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 → Refrigerant Circuit, Flushing with Refrigerant R134a or blowing through using compressed air and nitrogen → Refrigerant Circuit, Flushing with Compressed Air and Nitrogen ), the correct quantity of refrigerant oil is filled into the circuit → Approved Refrigerant Oils .