Volkswagen Polo Service & Repair Manual: Checking with Restrictor, Reservoir and A/C Compressor Regulator Valve -N280-, Externally Regulated A/C Compressor

Volkswagen Polo Service & Repair Manual / Refrrigerant R134a Servicing / Pressures, Checking / Checking with Restrictor, Reservoir and A/C Compressor Regulator Valve -N280-, Externally Regulated A/C Compressor

Note

Connecting service station. Refer to → Chapter „Connecting Service Station“.

Observe test requirements. Refer to → Chapter „Pressures, Checking“.

–	Bring engine speed up to 2000 RPM.

–	Pay attention to the A/C service station pressure gauge.

Note

Switching pressures for actuation of A/C Compressor Regulator Valve -N280- and Coolant Fan -V7- are vehicle-specific.

Refer to → Rep. Gr.87.

Specified Values

High-pressure side:

Increasing from initial pressure (when connecting pressure gauges) to 20 bar (290 psi).

Low-pressure side:

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

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

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

C -	Permissible tolerance range

Note

Under unfavorable conditions (very high ambient temperatures, high humidity), pressure on high-pressure side may increase to max. 29 bar (421 psi).

The control current -B- is shown in the measured value block.

The high pressure is shown in the measured value block. Refer to → Rep. Gr.87.

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.

The specified operating current for the regulator valve must be greater than 0.3 A in order to ensure reliable valve activation.

In the setting “maximum cooling output” control current is regulated to approximately 0.8 A (displayed in measured value block). Refer to → Rep. Gr.87.

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

Checking with Restrictor, Reservoir and A/C Compressor Regulator Valve -N280-, Externally Regulated A/C Compressor

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

Activation of A/C Compressor Regulator Valve -N280- is faulty.

Not enough refrigerant in refrigerant circuit

–	Check activation of A/C Compressor Regulator Valve -N280-.

–	Localize the 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

High pressure normal

Low pressure too low (see graph)

Required cooling output is not attained

Note

If no malfunction is found with this complaint, flush (clean) refrigerant circuit with refrigerant R134a. Refer to → Chapter „Refrigerant Circuit, Flushing (Cleaning) with Refrigerant R134a“. If that is not possible in this workshop, flush the refrigerant circuit with compressed air and remove moisture with nitrogen. Refer to → Chapter „Refrigerant Circuit, Flushing with Compressed Air and Nitrogen“.

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

Required cooling output is not attained

Activation of A/C Compressor Regulator Valve -N280- is faulty.

A/C compressor faulty.

–	Check activation of A/C Compressor Regulator Valve -N280-.

–	Flush (clean) refrigerant circuit. Refer to → Chapter „Refrigerant Circuit, Flushing (Cleaning) with Refrigerant R134a“.

–	Replace A/C compressor.

High pressure increases above specification

Low pressure drops only slightly

Required cooling output is not attained

Constriction or obstruction in refrigerant circuit

–	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 refrigerant circuit with compressed air and nitrogen

If no malfunction can be found:

–	Flush (clean) refrigerant circuit. Refer to → Chapter „Refrigerant Circuit, Flushing (Cleaning) with Refrigerant R134a“.

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

–	Flush refrigerant circuit with compressed air and nitrogen.

–	Replace reservoir.

–	Repeat test if function is not OK.

–	Flush (clean) refrigerant circuit. Refer to → Chapter „Refrigerant Circuit, Flushing (Cleaning) with Refrigerant R134a“.

–	Charge the refrigerant circuit.

–	Repeat the test.

High pressure normal

Low pressure too low (see graph)

The required cooling performance is obtained

Activation of A/C Compressor Regulator Valve -N280- is faulty.

A/C compressor faulty.

–	Check activation of A/C Compressor Regulator Valve -N280-.

–	Flush (clean) refrigerant circuit. Refer to → Chapter „Refrigerant Circuit, Flushing (Cleaning) with Refrigerant R134a“.

–	Replace A/C compressor.

Note

For the malfunction “high pressure normal, low pressure too low”, note the following: faulty, the evaporator can ice up or the cooling output is not reached.

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

Check measured values of Evaporator Vent Temperature Sensor -G263- or Evaporator Temperature Sensor -G308-.

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

Refer to → Rep. Gr.87.

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.

High and low pressure normal

Required cooling output is not attained

To much refrigerant oil in the circuit.

–	Discharge the refrigerant circuit.

–	Flush (clean) refrigerant circuit. Refer to → Chapter „Refrigerant Circuit, Flushing (Cleaning) with Refrigerant R134a“.

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 the A/C compressor is not replaced, the refrigerant oil should be drained from the A/C compressor via the oil drain plug. Out of the entire quantity of refrigerant oil, 50 grams should be put in the A/C compressor and the rest in the refrigerant circuit. Refer to vehicle-specific repair manual.

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