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Keeping your customers cool

With winter firmly behind us, dormant air conditioning systems are failing to reawaken; Rob Marshall looks at the latest news and repair tips for HVAC repairs.

While air conditioning leaks can be difficult to diagnose, even with UV dye, use common sense. This condenser leaked due not only to impact damage but also corrosion.

Neglect can be a form of abuse, especially when it comes to air conditioning. Many motorists seem oblivious that regular use of ‘air-con’ not only demists their interiors during the winter months but it also keeps the system ‘exercised’. Sadly, many owners remain unaware that the cost of fixing neglected air conditioning can eclipse the notional fuel savings many times over. Communicating this to your customer can help them to avoid expensive repair bills, as well as reassuring them that you have their best interests at heart. 




While the air conditioning system seems to be a standalone element, it works in conjunction with the car’s heater. The whole unit tends to be described as Heating, Ventilation and Air Conditioning (HVAC). Therefore, should you discover that there is insufficient pressure in the air conditioning system, it is worth interrogating the entire HVAC system diagnostically. Physical damage, such as inoperative, or broken, heater mixer flaps within the heater box, can give the impression that the air conditioning is not working. Therefore, your diagnostic procedure may take you beyond the basic air-conditioning circuit. 

Electric Vehicles and some Hybrids utilise compressors that are powered electrically and wired to the inverter. The car’s high-voltage circuit should be powered-down, before work starts. PAG oils cannot be used in their repair, because it is electrically-conductive.

Most issues stem from low refrigerant pressure. While most systems in good order discharge around 10% of their gas annually, leaks are not always easy to spot. Ultra-Violet leak tracer fluids have been essential to pin-point them; Primalec’s Glo-Leak has been a respected manufacturer of such products for over thirty years. While the company will be present at Automechanika Birmingham, showcasing its air conditioning service and repair solutions, it is worth noting that its latest Glo-Leak 1234 product is formulated for the latest synthetic R1234yf refrigerant and is back-compatible with the earlier R134a. Apart from using your own experience and procedures to guide you, Behr Hella Service has advised AT that it has updated its ‘know-how’ tool, which provides non-vehicle specific information about potential faults and remedies. 

2019 Parts and support news 

Behr Hella Service told us that it has formulated a comprehensive service package to support the independent workshop for 2019. This includes a free compressor app, which details vehicle-specific refrigerant and compressor oil-filling quantities. Expanding technical information and parts lines for hybrid and EV applications have been introduced too, including electric water pumps, alongside its usual range of Sanden electric compressors. Further information is available at the HELLA TECH WORLD portal. 


Annual replacement of the cabin filter and disinfection of the evaporator/air outlets presents valuable upsell opportunities, which AT will investigate soon. Monitoring the refrigerant pressure should be undertaken every two years, due to the natural depressurisation that takes place over time, and it is strongly recommended that the receiver/dryer is replaced too, although this can add significantly to the cost of a routine service. Consider also that, just as air conditioning and the car heater influence each other, so too does the engine’s cooling system. Therefore, adding it to your preventative maintenance programme is a wise idea. 

Laughing gas (all the way to the bank) 

Rising refrigerant prices continue to raise eyebrows. As R134a is 1,300 times more damaging than CO2 from a global warming perspective and degrades in 13 years, the EU is restricting production, which has led to price rises. On more recent cars (introduced progressively from 2012) R1234yf was introduced, which requires only 13 days to dissipate and is only four times as harmful as CO2 as a greenhouse gas. 

Since 2017, CO2 has been adopted as a refrigerant (R744), with obvious environmental benefits and, according to Behr Hella Service, it provides tremendous opportunities for its customers. While AT will examine CO2-based systems in more depth soon, the main differences include pressures ten times greater than those of a non-CO2 system, as well as different sealing methods employed, which must be respected during repair procedures. Primalec will be explaining more about CO2 systems in its Automechanika workshop session at 12.30pm on June 5th. 


Find the fault 

As with all repairs, spend time diagnosing the problem before ‘firing the parts cannon’. It has been known, for example, for technicians to blame a faulty dual mass flywheel, when the real culprit is a rattling compressor clutch. 

Spare part compatibility 

Check that any replacement matches the original component, including mountings and connections. Use new O-rings that are compatible with the refrigerant employed. Do not use unsuitable lubricants on O-rings and seals, this will contaminate the system. 

Keep the system sealed for as long as possible 

No connections should remain open for an extended period – use caps, or plugs, to reduce the amount of moisture from the atmosphere affecting the circuit. 

Renew the receiver/dryer 

This component is designed to absorb moisture. When the pressurised circuit is opened, the receiver/dryer is likely to become saturated. In some cases, silicate particles can break free and be distributed around the system, causing severe harm. New compressors can fail soon after replacement, if the reason behind the break- down is not established, or the expansion valve and receiver/drier are not renewed at the same time. 

Use two wrenches 

As the connections are formed from soft aluminium, they can distort easily; use two spanners, during loosening and tightening operations. 

Watch for sharp edges 

Panel and trim edges can damage components, such as condensers, hoses and cabling, so take extra care, especially when manoeuvring the parts into tight spaces. 

Final leak checks 

Once a repair is completed, the system must sustain a vacuum (negative pressure) to ensure that it is leak-tight, prior to being evacuated. This will remove all moisture from the system before it can be refilled with gas. 

PAG oil considerations 

PAG oil is hygroscopic. Unless you remove all the oil from the system and flush it through, prior to fitting a new compressor, you will have no idea of how much oil to add. An overfilled system causes ‘liquid lock’ in the compressor, promoting failure. Use the correct oils – never opt for a lubricant with a ‘universal’ specification. 

Observe specifications while filling 

Heed the quality and specification of refrigerant that
is specified by the vehicle manufacturer. Excessive pressures place extra strain on the compressor and its clutch (if fitted), unless a pressure switch cuts the power, first. After filling, start the engine and compare the values measured at the low and high pressure ports with the VM’s specifications. Verify the cold air temperature at the centre vent is comparable with that provided by the carmaker. 

Post-work considerations 

Protect the service connection valves and threads with clean protective caps and fit a service label sticker to the bonnet, or slam panel, as a record of the work performed. 

About Autotechnician
Autotechnician is a magazine published nine times a year, delivering essential information to independent garage owners and technicians in the UK. Delivered both digitally and in print, autotechnician provides readers with technical, training, business advice, product and news, allowing our readers to keep up to date with information they need to run and work within a modern workshop.
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