Volkswagen Golf Service & Repair Manual: Checking systems with an expansion valve and reservoir (with internally regulated air conditioner compressor)

Volkswagen Golf Service & Repair Manual / Air conditioning system with refrigerant R134a / Checking pressures on vehicles / 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 → Chapter.

–	Raise engine speed to 2,000 rpm.

–	Observe manifold gauge.

Note

The switch pressures and the versions of switches in the refrigerant circuit are vehicle-specific.

Pressures must be measured at the service connections; the fitting locations of these connections are vehicle-specific.

→ 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 in bar positive pressure.

B -	Low pressure in bar positive pressure.

C -	Permitted tolerance range.

Checking systems with an expansion valve and reservoir (with internally 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.

Too little refrigerant in circuit or expansion valve defective.

–	Extract some refrigerant from the refrigerant circuit.

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

–	Renew expansion valve.

–	Recharge refrigerant circuit.

–	Repeat check.

High pressure is normal,

Low pressure matches the diagram value,

The required cooling output is not delivered.

The quantity of refrigerant extracted is significantly less than the prescribed charge quantity.

–	Look for leaks using leak detector and rectify them.

–	Recharge refrigerant circuit.

–	Repeat check.

Note

If no fault can be determined and the function of the air conditioning system is not OK when the test is repeated, purge refrigerant circuit with refrigerant R134a (clean) → 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 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.

Expansion valve defective.

–	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, purge refrigerant circuit with compressed air and nitrogen and renew expansion valve.

If no faults are found:

–	Purge (clean) refrigerant circuit → Chapter.

–	Repeat check.

Note

If the air conditioning system is still not operating correctly after the refrigerant circuit has been purged with compressed air and nitrogen, the expansion valve must be renewed.

Possible deviation from specification

Possible cause of fault

Rectifying fault

High pressure and low pressure are normal at first,

After a while, the high pressure increases beyond the specification, and the low pressure falls to the diagram value or lower,

The cooling power called for is not delivered.

Expansion valve defective.

Moisture in the refrigerant circuit.

–	Examine the expansion valve for dirt or corrosion; renew if necessary.

–	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.

Note

When this fault occurs, always renew receiver.

Possible deviation from specification

Possible cause of fault

Rectifying fault

High pressure normal or too high (see diagram),

The required cooling output is not delivered.

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

Too much refrigerant in circuit.

Expansion valve or air conditioner compressor defective.

–	Extract some refrigerant from the refrigerant circuit.

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

–	Renew expansion valve.

–	Recharge refrigerant circuit.

–	Repeat test.

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

–	Recharge refrigerant circuit.

–	Repeat check.

Note

If the air conditioning system is still not operating correctly when the test is repeated, refit the expansion valve and purge the refrigerant circuit with compressed air and nitrogen. Then renew the air conditioner compressor and receiver.

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 power is not delivered.

The air conditioner compressor is defective.

–	Purge (clean) refrigerant circuit → Chapter.

–	Renew the air conditioner compressor and receiver.

Possible deviation from specification

Possible cause of fault

Rectifying fault

High pressure is normal,

Low pressure is too low (see diagram),

The cooling power required is delivered.

Expansion valve or air conditioner compressor defective.

–	Renew expansion valve.

–	Recharge refrigerant circuit.

–	Repeat check.

Note

If repeated check results in air conditioning system still not operating correctly, purge (clean) the refrigerant circuit → Chapter. Then renew the air conditioner compressor and receiver.

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

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.

Checking systems with a restrictor and collector (with internally regulated air conditioner compressor)

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

Checking systems with an expansion valve and reservoir (without regulated air conditioner compressor)

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