Volkswagen Golf Service & Repair Manual: Checking systems with a restrictor and collector (with internally 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 collector (with internally 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

Switch pressures for switches in refrigerant circuit are vehicle-specific.

The connection with a valve for the low-pressure switch or on the evaporator should only be used where the vehicle does not have a service connection on the low-pressure side and access to the connection on the air conditioner compressor or reservoir is not possible (measurement accuracy). This only applies to certain vehicles.

→ Rep. gr.87

Specifications:

High-pressure side:

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

Low-pressure side:

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

A -	High pressure (measured at the service connection) in bar positive pressure.

B -	Low pressure (measured at the connection with the valve at the air conditioner compressor or at the reservoir) in bar positive pressure.

C -	Permitted tolerance range.

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

E -	Permitted tolerance range.

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.

Insufficient refrigerant in circuit.

–	Look for leaks 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.

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.

The air conditioner compressor is defective.

–	Purge (clean) refrigerant circuit → Chapter.

–	Renew air conditioner compressor.

Possible deviation from specification

Possible cause of fault

Rectifying fault

High pressure rises above specification,

Low pressure falls quickly to the diagram value or lower,

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.

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

–	Purge (clean) refrigerant circuit → Chapter.

High pressure and low pressure are normal at first, but after a time,

The high pressure increases beyond the specified value,

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 receiver.

–	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.

The air conditioner compressor is defective.

–	Purge (clean) refrigerant circuit → Chapter.

–	Renew air conditioner compressor.

Note

If the fault is “high pressure normal, low pressure too low ” please note the following:

In this case, the evaporator may be iced up or the low-pressure switch for air conditioning system -F73- has switched off the air conditioning system compressor, although the correct quantity of refrigerant is present in the refrigerant circuit.

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.

Possible deviation from specification

Possible cause of fault

Rectifying fault

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.

Continuation of checking pressures

Where vehicles have a restrictor and reservoir, check these (with internally regulated air conditioning system compressor) → Chapter. ...

Checking systems with an expansion valve and reservoir (with internally regulated air conditioner compressor)

Note Connecting air conditioner service station → Chapter. Observe the test prerequisites → Cha ...

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