Volkswagen Workshop Service and Repair Manuals

Nominal values High pressure side: Gradual rise from outlet pressure (at the time of connecting the pressure gauge) up to a maximum pressure of 20 bar. Low pressure side:

Gradual fall of the outlet pressure (at the time of connecting the pressure gauge) to the value given in the diagram. A -  Low pressure (measured at the service terminal), expressed in absolute pressure bar. B -  Control current of the Adjustment valve for the air conditioning compressor -N280-. C -  Admissible tolerance limit.   Note t  The pressure measured in the high pressure side may, under adverse circumstances (extremely high ambient temperature and humidity), rise to almost 29 bar. t  Control current -B- is shown in the measurement values block. t  The high pressure measured by the High pressure sensor -G65- is indicated in the measurement values block → Vehicle diagnosis, testing and information system VAS 5051. t  The low pressure is automatically adjusted to a value within the tolerance limits, based on the control current of the Adjustment valve for the air conditioning compressor -N280-, within the power limits of the compressor. t  Under adverse conditions (extremely high ambient temperature and humidity), the compressor's power may not always be sufficient to reach the given value. t  The effective nominal current of the adjustment valve must be greater than 0.3 A to ensure its correct activation. t  For maximum cooling power, the control current is adjusted to values between 0.65 and 0.8 A (it varies from vehicle to vehicle and is indicated in the measurement values block). t  When pressure is expressed as absolute pressure, 0 (zero) bar corresponds to an absolute vacuum. Normal atmospheric pressure is equal to 1 (one) bar of absolute pressure. On most pressure gauge scales, 0 (zero) bar equals 1 (one) bar of absolute pressure (identifiable by the indication (–1) below the (0)).

Admissible deviation from the nominal value	Possible cause of the fault	Troubleshooting
l  High pressure remains constant or rises only marginally above the value measured with the engine stopped. l  Low pressure decreases rapidly to the value given in the diagram or below it. l  The desired cooling power is not reached.	t  Activation of the Adjustment valve for the damaged air conditioning compressor -N280-. t  The amount of refrigerant gas in the loop is too small.	–  Check operation of the Adjustment valve for the air conditioning compressor -N280-. –  Locate and eliminate the leak → Chapter. –  Refill the refrigerant gas loop → Chapter.
l  High pressure is normal. l  Low pressure matches the value given in the diagram. l  The desired cooling power is not reached.
l  High pressure is normal. l  Low pressure is very low (see diagram). l  The desired cooling power is not reached.	t  The amount of refrigerant gas in the loop is too small.	–  Suck refrigerant gas from the loop → Chapter. l  The quantity of refrigerant gas sucked is significantly less than the filling capacity indicated. –  Locate and eliminate the leak → Chapter. –  Refill the refrigerant gas loop → Chapter. –  Check again. l  The quantity of refrigerant gas sucked more or less matches the filling capacity indicated.
	t  The expansion valve is damaged.	–  Replace the expansion valve. –  Refill the refrigerant gas loop → Chapter. –  Check again.

t	If no fault is found, vent the refrigerant gas loop → Chapter.

t

Check measurement values for the Air outlet temperature sensor for the evaporator -G263- and operation of the Adjustment valve for the air conditioning compressor -N280-. If the measurement value for the High pressure sensor -G65- is incorrect, the evaporator may freeze or the cooling power is not be reached.

t	If the air conditioning continues to malfunction, after repeating the check, replace the expansion valve again and vent the refrigerant gas loop. Then, replace the compressor and the liquid tank/dryer filter.

t	In this type of fault, the evaporator may freeze even though there is an adequate amount of refrigerant gas in the refrigerant gas loop.

t

If the expansion valve is faulty (permanently closed or only partly open), the Adjustment valve for the air conditioning compressor -N280- is adjusted for maximum power and the low pressure decreases to the value given in the diagram or below it (the air conditioning compressor sucks the refrigerant gas from the low pressure side). Since the refrigerant gas cannot pass through the expansion valve, the cooling power is not reached and the high pressure may not rise or rise only marginally, as there is no energy transformation.

Admissible deviation from the nominal value	Possible cause of the fault	Troubleshooting
l  High pressure rises only marginally above the value measured with the engine stopped. l  Low pressure decreases only marginally. l  The desired cooling power is not reached.	t  Activation of the Adjustment valve for the damaged air conditioning compressor -N280-.	–  Check activation of the Adjustment valve for the air conditioning compressor -N280-.
	t  The air conditioning compressor is damaged.	–  Replace the air conditioning compressor.
l  High pressure rises above the nominal value. l  Low pressure decreases rapidly to the value given in the diagram or below it. l  The desired cooling power is not reached.	t  Activation of the Adjustment valve for the damaged air conditioning compressor -N280-.	–  Check activation of the Adjustment valve for the air conditioning compressor -N280-.
	t  Bottle neck or obstruction in the refrigerant gas loop.	–  Check manually whether the refrigerant gas has temperature gradients. l  A temperature gradient was detected in one of the components: –  Replace the component if one of its rigid or flexible lines is either folded or bottle necked. –  In case of obstruction, vent the refrigerant gas loop → Chapter. –  Refill the refrigerant gas loop → Chapter. –  Check again. l  No fault was detected: –  Refill the refrigerant gas loop → Chapter. –  Recheck in case of malfunction.
	t  The expansion valve is damaged.	–  Suck refrigerant gas from the loop → Chapter. –  Replace the expansion valve and the liquid tank / dryer filter. –  Refill the refrigerant gas loop → Chapter.

t	In this type of fault, the evaporator may freeze even though there is an adequate amount of refrigerant gas in the refrigerant gas loop.

t

If the expansion valve is damaged (permanently closed or only partly open), the Adjustment valve for the air conditioning compressor -N280- is adjusted for maximum power and the low pressure decreases to the value given in the diagram or below (the air conditioning compressor sucks the refrigerant gas from the low pressure side). Since the refrigerant gas cannot pass through the expansion valve, the cooling power is not reached and the high pressure may not rise or rise only marginally, as there is no energy transformation.

Admissible deviation from the nominal value	Possible cause of the fault	Troubleshooting
l  High and low pressure show normal values initially. l  After some time, the high pressure rises above the nominal values. l  The low pressure decreases to the values given in the diagram or below it. l  The desired cooling power is no longer reached.	t  Activation of the Adjustment valve for the damaged air conditioning compressor -N280-.	–  Check activation of the Adjustment valve for the air conditioning compressor -N280-.
l  High and low pressure are initially normal. l  After some time, the low pressure decreases to values below normal (the evaporator freezes). l  After some time, the low pressure decreases to values below normal (the evaporator freezes).	t  Humidity in the refrigerant gas loop.	–  Suck refrigerant gas from the loop → Chapter. –  Vent the refrigerant gas loop → Chapter. –  Replace the liquid tank / dryer filter. –  Remove the air from the refrigerant gas loop over at least 3 hours. –  Refill the refrigerant gas loop → Chapter. –  Recheck in case of malfunction. –  Refill the refrigerant gas loop → Chapter. –  Check again.

Note t  If the fault only appears after an extended period of operation or sporadically (the low pressure decreases to values lower than the nominal value and the evaporator freezes), only the dryer filter will need to be replaced. Correct the amount of refrigerant gas oil. Then, remove the air from the refrigerant gas loop over at least 3 hours. t  With this type of fault, it is not necessary to vent the refrigerant gas loop, as the amount of humidity in the system is minimal. Humidity may be extracted by means of a longer draining procedure. t  In this type of fault, the evaporator may freeze even though there is an adequate amount of refrigerant gas in the refrigerant gas loop.

Admissible deviation from the nominal value	Possible cause of the fault	Troubleshooting
l  High pressure is normal. l  Low pressure is very low (see diagram). l  The desired cooling power is not reached.	t  Activation of the Adjustment valve for the damaged air conditioning compressor -N280-.	–  Check activation of the Adjustment valve for the air conditioning compressor -N280-.
	t  The expansion valve is damaged.	–  Suck refrigerant gas from the loop → Chapter. –  Replace the expansion valve and the liquid tank / dryer filter. –  Refill the refrigerant gas loop → Chapter. –  Recheck in case of malfunction. –  Replace the air conditioning compressor.
	t  The air conditioning compressor is damaged.	–  Suck refrigerant gas from the loop → Chapter. –  Replace the air conditioning compressor. –  Refill the refrigerant gas loop → Chapter. –  Check again.

Note t  If a fault is detected “with high pressure normal, low pressure very low”, please observe the following: t  With this fault, the evaporator may freeze even though there is an adequate amount of refrigerant gas present in the refrigerant gas loop. t  Check measurement values for the Air outlet temperature sensor for the evaporator -G263- and operation of the Adjustment valve for the air conditioning compressor -N280-. If the measurement value for the High pressure sensor -G65- is incorrect, the evaporator may freeze or the cooling power is not be reached. t  If the fault is located in the Adjustment valve for the air conditioning compressor -N280- (the adjustment valve does not operate but the compressor continues to run), it is not necessary to vent the refrigerant gas loop. In this type of fault only the air conditioning compressor needs to be replaced (correct the amount of refrigerant gas oil in the new air conditioning compressor). t  If the expansion valve is faulty (permanently closed or only partly open), the Adjustment valve for the air conditioning compressor -N280- is adjusted for maximum power and the low pressure decreases to the value given in the diagram or below it (the air conditioning compressor sucks the refrigerant gas from the low pressure side). Since the refrigerant gas cannot pass through the expansion valve, the cooling power is not reached and the high pressure may not rise or rise only marginally, as there is no energy transformation.

Admissible deviation from the nominal value	Possible cause of the fault	Troubleshooting
l  High pressure is normal or very high. l  Low pressure is very high (see diagram). l  The air conditioning compressor is noisy (especially after starting). l  The desired cooling power is not reached.	t  Activation of the Adjustment valve for the damaged air conditioning compressor -N280-. t  There is excess refrigerant gas in the circuit.	–  Check activation of the Adjustment valve for the air conditioning compressor -N280-. –  Suck refrigerant gas from the loop → Chapter. l  The quantity of refrigerant gas removed more or less matches the filling capacity indicated: –  Replace the air conditioning compressor. l  The quantity of refrigerant gas removed is significantly greater than the filling capacity indicated. –  Refill the refrigerant gas loop → Chapter. –  Check again.
	t  There is excess refrigerant gas oil in the loop.	–  Suck refrigerant gas from the loop → Chapter. l  The quantity of refrigerant gas removed more or less matches the filling capacity indicated. –  Refill the refrigerant gas loop → Chapter. –  Check again.
	t  The expansion valve is damaged.	–  Suck refrigerant gas from the loop → Chapter. –  Replace the expansion valve and the liquid tank / dryer filter. –  Refill the refrigerant gas loop → Chapter. –  Recheck in case of malfunction. –  Replace the air conditioning compressor.
	t  The air conditioning compressor is damaged.	–  Suck refrigerant gas from the loop → Chapter. –  Replace the air conditioning compressor. l  The quantity of refrigerant gas removed is significantly greater than the filling capacity indicated. –  Refill the refrigerant gas loop → Chapter. –  Check again.

t

If the fault is located in the Adjustment valve for the air conditioning compressor -N280- (the adjustment valve does not operate but the compressor continues to run), it is not necessary to vent the refrigerant gas loop. In this type of fault only the air conditioning compressor needs to be replaced (correct the amount of refrigerant gas oil in the new air conditioning compressor).

t

If the expansion valve is faulty (permanently closed or only partly open), the Adjustment valve for the air conditioning compressor -N280- is adjusted for maximum power and the low pressure decreases to the value given in the diagram or below it (the air conditioning compressor sucks the refrigerant gas from the low pressure side). Since the refrigerant gas cannot pass through the expansion valve, the cooling power is not reached and the high pressure may not rise or rise only marginally, as there is no energy transformation.

Admissible deviation from the nominal value	Possible cause of the fault	Troubleshooting
l  High and low pressure show normal values. l  The desired cooling power is not reached.	t  Activation of the Adjustment valve for the damaged air conditioning compressor -N280-. t  There is excess refrigerant gas oil in the loop.	–  Check operation of the Adjustment valve for the air conditioning compressor -N280-.
l  High and low pressure show normal values. l  The air conditioning compressor is noisy (especially after starting). l  The desired cooling power is not reached.	t  There is excess refrigerant gas oil in the loop.	–  Suck refrigerant gas from the loop → Chapter. –  Refill the refrigerant gas loop → Chapter. –  Check again.
	t  The expansion valve is damaged.	–  Replace the expansion valve.

t	Excessive filling of refrigerant gas oil may occur, for example, when the compressor is replaced without correcting the amount of refrigerant gas oil.

t

If the expansion valve is damaged (always open), the temperature in the evaporator is not regulated in order to ensure that the refrigerant gas comes out of the evaporator in gaseous form. Under certain operating conditions, the compressor may suck in liquid drops, causing noise (liquid cannot be condensed).