Skoda Workshop Service and Repair Manuals

Specified values High-pressure side: From the output pressure (when connecting the pressure gauge) rising up to maximum 20 bar overpressure. Low-pressure side:

From the output pressure (when connecting the pressure gauge) dropping to diagram value. A -  Low pressure (measured on the service connection) in bar absolute pressure. B -  The control current for the regulating valve for compressor of air conditioning system -N280- in amps. C -  Permissible tolerance range (valid for compressor load between 10...90%)   Note t  The pressure on the high-pressure side can rise to maximum 29 bar under unfavourable conditions (very high ambient temperatures, high humidity) and the performance of the air conditioning system may not always suffice in order to reach the given value. t  The control current -B- is indicated → Vehicle diagnostic tester in the measured value block of the control and display unit for air conditioner Climatronic -E87- or the Climatronic control unit -J255-. t  The high pressure measured by the high pressure sender -G65- is displayed in the measured value block → Vehicle diagnostic tester. t  The low pressure settles in the tolerance range in line with the control current for the regulating valve for compressor of air conditioning system -N280- within the performance range of the AC compressor. t  The specified working current for the regulating valve must be greater than 0.3 A so that the regulating valve is easily actuated. t  On the setting „maximum refrigerating capacity“ the control current is regulated to approx. 0.65 A up to 0.8 A (specifically designed for vehicles, displayed in the measured value block).

Possible deviation from the specified value	Possible cause of fault	Rectifying fault
l  High pressure remains constant or increases only slightly (above the pressure while engine is not running), l  Low pressure drops quickly to diagram value or lower, l  the required cooling capacity is not reached.	t  The actuation of the regulating valve for compressor of air conditioning system -N280- is incorrect. t  Too little refrigerant in the circuit. t  Expansion valve defective.	–  Check the actuation of the regulating valve for compressor of air conditioning system -N280-. –  Drain the refrigerant from the refrigerant circuit. l  The volume of refrigerant suctioned out is considerably less than the specified filling capacity:
l  High pressure is normal, l  Low pressure corresponds to the diagram value, l  the required cooling capacity is not reached.		–  Search for leaks with the leak detector, eliminate. –  Newly filling the refrigerant circuit. –  Repeat check.
l  High pressure is normal, l  Low pressure is too low (see diagram), l  the required cooling capacity is not reached.		l  The volume of refrigerant suctioned out corresponds approximately to the specified filling capacity: –  Replace expansion valve. –  Newly filling the refrigerant circuit. –  Repeat check.

t	If no fault is found for this complaint, clean the refrigerant circuit → Chapter.

t

Check the measured values of the evaporator vent temperature sender -G263- and the actuation of the regulating valve for compressor of air conditioning system -N280-. If the measured value of the evaporator vent temperature sender -G263- is incorrect, the evaporator can ice up and the cooling capacity is not reached.

t

If the function of the air conditioning system is not O.K. when repeating the test after replacing the expansion valve (reexchange expansion valve), clean refrigerant circuit → Chapter. Subsequently replace AC compressor and fluid reservoir with dessicator or only dessicator (specifically designed for vehicles).

t

If the expansion valve is defective (it is closed constantly or it does not open up wide enough) the regulating valve for compressor of air conditioning system -N280- is actuated to maximum performance and the low pressure drops to the diagram value or lower (the AC compressor suctions the refrigerant out of the low pressure side). As no refrigerant can flow through the expansion valve, the cooling capacity is not reached, perhaps the high pressure does not rise or only rises slightly because no energy turnover exists.

t	If this fault occurs, it can happen that the evaporator ices up although the volume of refrigerant in the circuit is O.K.

Possible deviation from the specified value	Possible cause of fault	Rectifying fault
l  High pressure increases only slightly above the pressure while engine is not running, l  Low pressure drops only slightly, l  the required cooling capacity is not reached.	t  The actuation of the regulating valve for compressor of air conditioning system -N280- is incorrect. t  AC compressor defective.	–  Check the actuation of the regulating valve for compressor of air conditioning system -N280-. –  Clean the refrigerant circuit → Chapter. –  Replace AC compressor.

Possible deviation from the specified value	Possible cause of fault	Rectifying fault
l  High pressure increases above the specified value, l  Low pressure drops quickly to diagram value, l  the required cooling capacity is not reached.	t  The actuation of the regulating valve for compressor of air conditioning system -N280- is incorrect. t  Constriction or blockage in the refrigerant circuit. t  Expansion valve defective.	–  Check the actuation of the regulating valve for compressor of air conditioning system -N280-. –  Feel the temperature gradient of the refrigerant circuit with the hand. l  A temperature gradient is noticed on a component: –  In case a hose line or a pipe is bent or constricted, replace this component. –  In case of a blockage, clean refrigerant circuit → Chapter, if necessary replace the expansion valve. l  If no fault is found: –  Clean refrigerant circuit → Chapter, if necessary replace expansion valve and fluid reservoir with dessicator or only dessicator (specifically designed for vehicles). –  Repeat check.

t	If this fault occurs, it can happen that the evaporator ices up although the volume of refrigerant in the circuit is O.K.

t

If the expansion valve is defective (it is closed constantly or it does not open up wide enough) the regulating valve for compressor of air conditioning system -N280- is actuated to maximum performance and the low pressure drops to the diagram value or lower (the AC compressor suctions the refrigerant out of the low pressure side). As no refrigerant can flow through the expansion valve, the cooling capacity is not reached, perhaps the high pressure does not rise or only rises slightly because no energy turnover exists.

Possible deviation from the specified value	Possible cause of fault	Rectifying fault
l  High pressure and low pressure is normal at first, after a certain period of operating time: –  the high pressure increases above the specified value, –  the low pressure drops to diagram value or lower, –  the required cooling capacity is no longer reached.	t  The actuation of the regulating valve for compressor of air conditioning system -N280- is incorrect. t  Humidity in the refrigerant circuit.	–  Check the actuation of the regulating valve for compressor of air conditioning system -N280-. –  Check expansion valve for dirt or corrosion, replace if necessary. –  Replace fluid reservoir with dessicator or only dessicator (specifically designed for vehicles) see notes.
l  High pressure and low pressure is normal at first, after a longer period of operating time: –  if the low pressure drops below the specified value (evaporator ices up).		–  Evacuate the refrigerant circuit for at least 3 hours. –  Repeat the test after refilling the circuit.

t

If problems arise due to humidity in the refrigerant circuit only after a longer operating time or only occasionally (the low pressure drops below the specified value and the evaporator ices up), it is adequate to replace the dessicator (the volume of refrigerant oil must be adapted → Chapter). Subsequently the refrigerant circuit must be evacuated for at least 3 hours.

t

First of all, it is not required to clean the refrigerant circuit for this complaint (to flush with refrigerant R134a or to blow through with compressed air and nitrogen), as normally only a small amount of humidity is present in the system which can be removed through a longer period of evacuation.

t	If this fault occurs, it can happen that the evaporator ices up although the volume of refrigerant in the circuit is O.K.

t	Due to a fault on the evaporator vent temperature sender -G263- the refrigerant circuit can also ice up. For this complaint, also observe the measured value of this sender → Vehicle diagnostic tester

Possible deviation from the specified value	Possible cause of fault	Rectifying fault
l  High pressure is normal, l  Low pressure is too low (see diagram), l  the required cooling capacity is reached.	t  The actuation of the regulating valve for compressor of air conditioning system -N280- is incorrect. t  Expansion valve or AC compressor defective.	–  Check the actuation of the regulating valve for compressor of air conditioning system -N280-. –  Clean the refrigerant circuit. → Chapter, if necessary replace expansion valve and fluid reservoir with dessicator or only dessicator (specifically designed for vehicles) see notes. –  Repeat the test after refilling the circuit. –  If the function is N.O.K., replace compressor.

t	If the fault „high pressure is normal, low pressure is too low“ occurs, please observe the following: If this fault occurs it can happen that the evaporator ices up although the volume of refrigerant in the circuit is O.K.

t

If the fault occurs on the regulating valve for compressor of air conditioning system -N280- (the regulating valve is not actuated and the AC compressor however keeps running) it is not required to clean the refrigerant circuit (flush with refrigerant R134a or blow through with compressed air and nitrogen). If this fault occurs, it is sufficent to replace the AC compressor (adapt the volume of refrigerant oil in the new AC compressor → Chapter).

t

If the expansion valve is defective (it is closed constantly or it does not open up wide enough) the regulating valve for compressor of air conditioning system -N280- is actuated to maximum performance and the low pressure drops to the diagram value or lower (the AC compressor suctions the refrigerant out of the low pressure side). As no refrigerant can flow through the expansion valve, the cooling capacity is not reached, perhaps the high pressure does not rise or only rises slightly because no energy turnover exists.

t	Due to a fault on the evaporator vent temperature sender -G263- the refrigerant circuit can also ice up. Also observe the measured value of this sender → Vehicle diagnostic tester

Possible deviation from the specified value	Possible cause of fault	Rectifying fault
l  High pressure is normal or too high, l  Low pressure is too high (see diagram), l  the AC compressor makes noises (especially after switching it on), l  the required cooling capacity is not reached.	t  The actuation of the regulating valve for compressor of air conditioning system -N280- is incorrect. t  Too much refrigerant in the circuit. t  Expansion valve defective.	–  Check the actuation of the regulating valve for compressor of air conditioning system -N280-. –  Drain the refrigerant from the refrigerant circuit. l  The volume of refrigerant suctioned out is considerably more than the specified filling capacity: –  Newly fill the refrigerant circuit and repeat the test. l  The volume of refrigerant suctioned out corresponds approximately to the specified filling capacity: –  Replace expansion valve. –  Newly fill the refrigerant circuit and repeat the test. –  If the function is N.O.K.:
	t  Too much refrigerant oil in the circuit. t  AC compressor defective.	–  Drain the refrigerant from the refrigerant circuit. –  Clean the refrigerant circuit. → Chapter, replace fluid reservoir with dessicator or only dessicator (specifically designed for vehicles). –  Newly fill the refrigerant circuit and repeat the test. –  If the function is N.O.K., replace compressor.

The cause of this fault may also be a surplus of refrigerant oil in the circuit. Over-filling with refrigerant oil can occur if, for example, the AC compressor was replaced without adapting the volume of refrigerant oil.

Possible deviation from the specified value	Possible cause of fault	Rectifying fault
l  High pressure and low pressure is normal, l  The required cooling capacity is not reached.	t  The actuation of the regulating valve for compressor of air conditioning system -N280- is incorrect. t  Too much refrigerant oil in the circuit. t  Expansion valve defective.	–  Check the actuation of the regulating valve for compressor of air conditioning system -N280-. –  Clean the refrigerant circuit. → Chapter. –  Newly fill the refrigerant circuit and repeat the test.
l  High pressure and low pressure is normal, l  the AC compressor makes noises (especially after switching it on), l  the required cooling capacity is not reached.		–  If the function is N.O.K., replace expansion valve.

t	Over-filling with refrigerant oil can occur if, for example, the AC compressor was replaced without adapting the volume of refrigerant oil.

t

If the expansion valve is defective (always open), the evaporator temperature is no longer regulated in such a way that only gaseous refrigerant leaves the evaporator. Under certain operating conditions, liquid drops can then be sucked into the AC compressor, this then leads to noises (liquid cannot be compressed).