Volkswagen Golf Service & Repair Manual: Checking systems with a restrictor and reservoir and air conditioner compressor regulating valve -N280- (with externally regulated air conditioner compressor)

Volkswagen Golf Service & Repair Manual / Air conditioning system with refrigerant R134a / Checking pressures on vehicles / Checking systems with a restrictor and reservoir and air conditioner compressor regulating valve -N280- (with externally regulated air conditioner compressor)

Note

Connecting air conditioner service station → Chapter.

Observe the test prerequisites → Chapter.

–	Raise engine speed to 2,000 rpm.

–	Observe air conditioner service station pressure gauge.

Note

Switching pressures for the air conditioner compressor regulating valve -N280- and the radiator fan -V7- are vehicle-specific.

→ Rep. gr.87

Specifications:

High-pressure side:

Rising from starting pressure (when pressure gauge is connected) to 20 bar.

Low-pressure side:

Falling from starting pressure (when pressure gauge is connected) to diagram value.

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

B -	Control current for the air conditioner compressor regulating valve -N280-.

C -	Permitted tolerance range.

Note

Under unfavourable conditions (very high ambient temperatures, high atmospheric humidity), the pressure on the high-pressure side can increase to a maximum of 29 bar.

The control current -B- is indicated in the measured values block.

The high pressure is indicated in the measured values block → Rep. gr.87.

The low pressure is adjusted to within tolerances within the output range for the air conditioner compressor depending on the control current for the air conditioner compressor regulating valve -N280-.

Under unfavourable conditions (very high ambient temperatures, high atmospheric humidity), the output may be insufficient to achieve the specification in every case.

The set working current for the regulating valve must be greater than 0.3 A to ensure that the regulating valve is reliably activated.

At the setting for “maximum cooling power”, the control current should be approx. 0.8 A (indicated in the measured values block) → Rep. gr.87.

Absolute pressure means that 0 bar corresponds to an absolute vacuum. The normal ambient pressure corresponds to 1 bar absolute pressure. On most pressure gauges, a reading of 0 bar corresponds to an absolute pressure of one bar (which is confirmed by the existence of - 1 bar marking beneath the 0 scale marking).

Checking systems with a restrictor and reservoir and air conditioner compressor regulating valve -N280- (with externally regulated air conditioner compressor)

Possible deviation from specification

Possible cause of fault

Rectifying fault

High pressure remains constant or increases only slightly (above the pressure measured when the engine is stopped),

Low pressure falls quickly to the diagram value or lower,

The required cooling output is not delivered.

Actuation of air conditioner compressor regulating valve -N280- is defective.

Insufficient refrigerant in circuit.

–	Check actuation of air conditioner compressor regulating valve -N280-.

–	Look for leaks using leak detector and rectify them.

–	Recharge refrigerant circuit.

High pressure is normal,

Low pressure matches the diagram value,

The required cooling output is not delivered.

High pressure is normal,

Low pressure is too low (see diagram),

The required cooling output is not delivered.

High pressure is normal,

Low pressure is too low (see diagram),

The required cooling output is not delivered.

Note

If no fault can be found for this complaint, purge (clean) refrigerant circuit with refrigerant R134a → Chapter. If this is not possible in your workshop, blow through refrigerant circuit with compressed air and dry with nitrogen → Chapter.

Possible deviation from specification

Possible cause of fault

Rectifying fault

High pressure increases only slightly above the pressure measured when the engine is stopped,

Low pressure falls only slightly,

The required cooling output is not delivered.

Actuation of air conditioner compressor regulating valve -N280- is defective.

The air conditioner compressor is defective.

–	Check actuation of air conditioner compressor regulating valve -N280-.

–	Purge (clean) refrigerant circuit → Chapter.

–	Renew air conditioner compressor.

High pressure rises above specification,

Low pressure falls only slightly,

The required cooling output is not delivered.

Restriction or obstruction in the refrigerant circuit.

–	Feel the refrigerant circuit with the hand to sense the temperature gradient.

At one component a temperature gradient will be detected:

–	If a hose or pipe is kinked or crushed, renew it.

–	In case of an obstruction, blow through refrigerant circuit with compressed air and nitrogen.

If no faults are found:

–	Purge (clean) refrigerant circuit → Chapter.

High pressure and low pressure are normal at first, but after a while, the high pressure increases beyond the specification,

The low pressure falls to the diagram value or lower,

The cooling power called for is not delivered.

Moisture in the refrigerant circuit.

–	Blow through refrigerant circuit with compressed air and nitrogen.

–	Renew reservoir.

–	Repeat the check; if the system does not operate correctly

–	Purge (clean) refrigerant circuit → Chapter.

–	Recharge refrigerant circuit.

–	Repeat check.

High pressure is normal,

Low pressure is too low (see diagram),

The cooling power required is delivered.

Actuation of air conditioner compressor regulating valve -N280- is defective.

The air conditioner compressor is defective.

–	Check actuation of air conditioner compressor regulating valve -N280-.

–	Purge (clean) refrigerant circuit → Chapter.

–	Renew air conditioner compressor.

Note

If the fault is “high pressure normal, low pressure too low ” note the following: if faulty the evaporator could ice up or the required cooling output is not delivered.

In this case, the evaporator may ice up although the correct quantity of refrigerant is present in the refrigerant circuit.

Check the measured value of the evaporator output temperature sender -G263- or evaporator temperature sensor -G308-.

Check the actuation of the air conditioner compressor regulating valve -N280-

→ Rep. gr.87

Possible deviation from specification

Possible cause of fault

Rectifying fault

High pressure normal or too high,

Low pressure too high (see diagram),

The air conditioner compressor is noisy (especially immediately after being switched on),

The required cooling output is not delivered.

Too much refrigerant in circuit.

–	Extract some refrigerant from the refrigerant circuit.

The quantity of refrigerant extracted is about equal to the prescribed charge quantity:

–	Renew the air conditioner compressor.

The quantity of refrigerant extracted is significantly greater than the prescribed charge quantity:

–	Recharge refrigerant circuit.

–	Repeat check.

High-pressure and low-pressure are normal,

The required cooling output is not delivered.

Too much refrigerant oil in circuit.

–	Drain refrigerant circuit.

–	Purge (clean) refrigerant circuit → Chapter.

High-pressure and low-pressure are normal,

The air conditioner compressor is noisy (especially immediately after being switched on),

The cooling power required is delivered.

Note

Overfilling with refrigerant oil can occur if the refrigerant oil level was not checked after the air conditioner compressor was renewed.

If the air conditioner compressor is not to be replaced, drain refrigerant oil from air conditioner compressor via the drain plug. From the total amount of refrigerant oil, fill 50 g direct into air conditioner compressor and fill remainder in refrigerant circuit according to → vehicle-specific workshop manual.

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