Worksheet 3 – Work steps with service station (solution)

1. Worksheet 3 – Work steps with service station (solution) • Correct procedures for working on air conditioning systems What must be observed for the individual work steps with an air conditioning service station? To do this, see ELSA (workshop manual "Air conditioning systems with refrigerant R134a"), the vehicle-specific workshop manuals and the operating instructions from the service station. 1. Before connecting the service station to the vehicle: • Check refrigerant volume and oil level of vacuum pump. • Check refrigerator oil, different types depending on the make of compressor • Observe details specific to the service unit from the relevant operating instructions, such as releasing the transportation device of the internal scales, etc. • Avoid extension leads. If absolutely necessary, use cable with a thickness of at least 2.5mm² cross section • The shutoff valves should be closed, hoses should be purged. • Ensure that no PAG oil from any previous service process falsifies the test results. • etc.

2. Worksheet 3 – Work steps with service station (solution) • Correct procedures for working on air conditioning systems 2. Connect A/C service station for measurements and checks: • If the repair history of the vehicle is unknown, the condition of the refrigerant should be checked individually to see if it has degraded or for the presence of foreign substances. • Remove cover caps of extraction and charger valves. Check the seal of each cap when doing this. • Never open the service connections when the engine/air conditioning system is in operation – leave the ignition switched off. • Do not open quick release couplings until an optimal connection can be assured. This prevents damage to the extraction and charger valves. • Wear protective clothing and observe safety regulations. • etc…

3. Worksheet 3 – Work steps with service station (solution) • Correct procedures for working on air conditioning systems 3. Extract the refrigerant with the service station: • The refrigerant circuit must be emptied … if worked is to be carried out on it, … the refrigerant volume cannot be determined properly, … if prescribed by safety measures, e.g. alignment and welding work in the area of pipe assemblies in the refrigerant circuit. • On vehicles with A/C compressor without magnetic coupling, the engine should run for < 10 minutes with emptied refrigerant circuit (A/C compressor runs on). The engine speed must not exceed 2000 revolutions per minute. • As soon as the refrigerant has been purged, the system should be opened for the repair measure. Otherwise, an unwanted increase in pressure could arise from refrigerant being given off from the oil. This could cause injuries.  • etc…  

4. Worksheet 3 – Work steps with service station (solution) • Correct procedures for working on air conditioning systems 4. Draining and disposing of extracted refrigerator oil: • It is quite possible for refrigerant oil to be extracted out of the refrigerant circuit with the refrigerant. To safeguard lubrication of the A/C compressor, the refrigerant oil volume may have to be supplemented with fresh oil. • Wear protective clothing, observe safety regulations. Refrigerator oil is extremely hygroscopic (draws in water). • Observe country-specific disposal regulations. Used oil can always contain a quantity of dissolved refrigerant that can outgas. Storage containers capable of withholding pressure and with a pressure relief valve are necessary. • Do not mix with other oils – hazardous waste – See also trade service handbook "Environmental protection" • ….

5. Worksheet 3 – Work steps with service station (solution) • Correct procedures for working on air conditioning systems 5. Measure volume of extracted refrigerator oil and recalculate: • Always use new PAG oil. The PAG oils suitable for refrigerant R134a are extremely hygroscopic and cannot be mixed with other oils. Therefore, seal opened container again immediately to guard against any ingress of moisture. Refrigerant oil ages from moisture and acids. It becomes dark, viscous and reacts aggressively with metals. • Top up extracted refrigerant oil with an additional 10 cm³ (rule of thumb) of new oil. • Note different types of PAG oils, depending on the compressors/manufacturers (Denso, Sanden, Zexel etc.) installed – see workshop manual or ETKA • …. 6. Purging refrigerant circuit with service station: • Before charging the refrigerant circuit with refrigerant, the system has to be purged. 45 minutes with 1 evaporator system and 60 minutes if 2 evaporators are installed. Furthermore, moisture is drawn out of the system. So, the longer the better. The purging time does, however, depend on any preceding repair. This should be explained by the trainer, always with reference to statements from the workshop manual. • etc…

6. Worksheet 3 – Work steps with service station (solution) • Correct procedures for working on air conditioning systems 7. During and after purging: • During purging, pressure may suddenly increase in the system. From a reduction in pressure in the refrigerant circuit, the refrigerant in the oil may outgas partly. This can be seen at the pressure gauge and it can also be heard. This is not unusual! • After purging, many service stations run through a vacuum test automatically. Note: A leak test of the system using vacuum pressure does not simulate the real operating status of a refrigerant circuit. Vacuum pressure is almost always present. • If the vacuum pressure does not remain: Fill 100 g of refrigerant in the refrigerant circuit, inc. leak detection additive, search for the leak using leak detection system -VAS 6196- or -VAS 6201- and rectify. Leak detection unit -V.A.G 1796- can also be used. Purge the refrigerant circuit once again. Only when the vacuum pressure is stable can the refrigerant circuit be filled. • Alternatively, the refrigerant circuit can be checked for leaks using nitrogen under pressure (max. 15 bar). The trainer will need to provide further details. • ….

7. Worksheet 3 – Work steps with service station (solution) • Correct procedures for working on air conditioning systems 8. Charging process with refrigerator oil and refrigerant: • The refrigerator oil is supplemented with refrigerant after purging and before charging. • Internal oil charging with service station or external charging with special tools from refrigerant equipment suppliers or with an injector and high pressure pump. • Charge with refrigerant – first close quick release couplings so that the filler hoses can be precharged. After precharging (or prefilling), open the quick release couplings and allow the prescribed volume of refrigerant to flow into the circuit. • …. 9. Bringing air conditioning system into operation after a new charge: • If the A/C compressor was removed, it should be cranked over by hand at the poly-V-belt pulley/freewheel approx. 10 times before bringing into operation. This prevents damage from liquid being compressed in the A/C compressor when the air conditioning system is switched on for the first time. • Additional instructions should be gleaned from the workshop manual "Air conditioning systems with refrigerant R134a – Charging refrigerant circuit with A/C service station". • ….

8. Worksheet 3 – Work steps with service station (solution) • Correct procedures for working on air conditioning systems 10. With system pressures after charging and when the air conditioning system is in operation: • When the engine is stationary and the air conditioning system is charged, the pressure in the system should be equal throughout. The pressure depends on the ambient temperature. At 20°C, the pressure is approx. 5 bar. • The refrigerant circuit should then be checked to ensure it is working properly. When the compressor starts to run, the low pressure range should fall to approx. 1.8 bar. High pressure should rise proportionally. • Hand test: High pressure lines warm to touch, low pressure lines cold • A full system test can be carried out in a relatively short time. Adjust max. cooling output and deactivate the condenser function (cover) - a pressure increase is expected in the high pressure range, which results in an increased radiator fan speed up to deactivation of the compressor. To trigger deactivation, the engine speed also has to be increased slightly. • ….

9. Worksheet 3 – Work steps with service station (solution) • Correct procedures for working on air conditioning systems 11. When disconnecting the hoses at the extraction and charger valves after service: • Wear protective clothing, observe the safety regulations. • First close the quick release couplings, then drain the charge hoses using the extraction or purging function on the service station. Caution – If it is not possible to do this properly, a quick release coupling may not be able to close or an extractor or charge valve may not work properly. • …. 12. Charging service station with new refrigerant and refrigerator oil from reservoir tanks: • To do this, please observe the operating instructions of the individual service stations. • The type of refrigerant reservoir tank should also be known as the position of the bottle when extracting is dictated by this. Normally standing reservoir tank, or reservoir tanks from which the refrigerant is taken if the tank is upside down. • ….