Step-by-Step Diagnostics by Nissens Automotive
As more new energy vehicles (NEVs), which include hybrid and electric vehicles, take to the roads, more will come into the workshop for routine climate system service, maintenance, or repair. However, the technicians undertaking this work need to be aware that they require special handling and safety procedures, as well as specialist knowledge to complete it successfully.
Using the thermal system as an example, many NEVs rely on a heat pump solution, which is an advanced system compared to a standard air conditioning (AC) loop.
Unlike the AC in a conventional vehicle, the heat pump-based system is capable of both heating and cooling. It also manages the temperature of the vehicle’s electric motor, battery pack and power electronics. In fact, the system functions as the vehicle’s thermal management system and helps the car conserve battery life and extend its total range.
The heat pump is a very energy-efficient thermal solution as it ensures optimal heating and cooling performance, but is not as demanding on the vehicle’s battery because fewer PTC heaters are needed to reach the same comfort level.
The heat pump incorporates more and different parts, and many of which would be mechanical in a conventional vehicle are fully electric in NEVs. For example, a high-voltage (HV), fully electric AC compressor is required to keep the system fully functional, even when the vehicle is not running. Furthermore, several electronic valves govern the various directional flows inside the loop. Other parts include more heat exchangers, such as the cabin heat condenser or the so-called, chiller, a water-cooler heat exchanger. These additional components add another level of complexity to the system’s maintenance.
Although some service procedures are similar to those of conventional vehicles, remember that hybrid and electric AC systems operate as thermal management systems, which means they must be fully functional in all seasons, not only for comfort, but also to ensure the correct operation of other systems. In fact, many NEVs will not start if the AC system is malfunctioning because of the risk of damage to the battery and the electric drive components. So, regular system maintenance is crucial.
Furthermore, it’s important to remember that many parts in the NEV AC system are also HV and require special safety procedures. So, consult the manufacturer’s safety guidelines to ensure their safe handling.
The most common failures include leakages, improper compressor lubrication, inner loop contamination and compressor burnout. Lower system performance or a total system failure are consequences of not addressing these problems quickly.
Hybrid vehicles with an engine cooling system working along with the AC loop can suffer potential failures in either system, which may impact the overall heating or cooling performance and, thus, battery performance.
Poor interior climate control is often the first symptom of a problem with the system.
Start any NEV’s heat pump system inspection like any other conventional AC system, so first, check to ensure the system is working according to the set parameters. Study the manufacturer’s guide on the number of heating/cooling functions and test them one by one, but keep in mind outside temperature can affect how the refrigerant flows through the system. If the system is functioning correctly, the valves that steer flows in the loop will open or close relative to ambient temperature. If it isn’t, there’s a risk that components could break down.
On initial inspection, include the service steps that are standard for the conventional AC system, which include:
Often, manufacturers provide no specific service procedures, so the following best practice guidance should be applied universally to NEVs and heat pump systems.
The vehicle’s original equipment (OE) documentation is important because obtaining as much information before undertaking the work is key. Therefore, system layout information, technical notes, bulletins, and service procedures will help the process and enable correct diagnostics.
Remember, safety is the key when working with HV systems. However, only power the system down if the HV system must be opened, to replace the AC compressor, for example. There’s no need to power down for a diagnostics test for temperature or pressure.
Only certified technicians applying the correct safety protocols can carry out service work, and they must follow dedicated procedures and use protective equipment and tools. It is also wise to take the time to learn the layout of the electrical system circuit beforehand.
In addition, disabling the HV system differs across make and model, so retrieve and study the required manufacturer documentation before performing the disconnection operation.
System evacuation and charging procedures may require a special OBD command to release the flow’s directing valves and keep in mind that a heat pump design loop may have several valves to control the inside flows. Finally, the volume of refrigerant can be significantly larger than a conventional system.
Digital tools such as a thermometer, wireless clamps and gauges etc. make the inspection process easier and more convenient, especially when servicing the advanced loops associated with the heat pump, for example.
In addition, HV tools and personal protective clothing and use only approved equipment and insulated tools certified for 1,000 volts. Only trained and authorised professionals can work on HV installations, and they should never work on them alone.
However, if the system is charged with R744 (CO2), approved tools for use with the refrigerant will be required. The recovery and filling station, connector, hoses, and pressure gauges for example, must be R744 (CO2) dedicated. Although their function is the same as for R1234yf, the higher work pressure of R744 (CO2) can be ten times greater, so the tools must be able to withstand these pressures. In addition, the system’s lubricant must be specific for R744 (CO2) and could be POE or PAG. Therefore, look at the specification on the compressor to double-check that the correct oil is used.
This device raises the temperature of the inlet of the compressor. Use a thermometer to check the temperature difference between the inlet and the outlet to check that the refrigerant coming from the high side of the AC system raises the temperature.
The valves can be checked by using the OBD scan tool, but this does not necessarily reveal if the valve is slightly open, so measure the temperature on each side of the valve. If the valve is fully closed, there will be a significant temperature difference. However, if the temperature of the tube on the outlet is lower, you know that the valve is slightly open because the refrigerant is starting to expand. Measuring the electrical current of the valves using a multimeter can also be helpful to determine if the valve receives a proper signal to close or open, although OE data related to operational voltage data must be obtained to perform such a diagnosis.
These are the same type as in a regular AC system, but more of them control the advanced functionality of the flows in the heat pump design loop with more valves and reverse flows. Use a scan tool to test them or simply use a heat source to set off the sensor to check it reacts.
Since there is only one low-side and high-side service port, these may be difficult to check without a scan tool as it won’t be possible to get an accurate reading at specific sensors.
Check regularly for dirt, deterioration and any damage to the heat exchanging surface because, if there is no heat transfer through the condenser, the refrigerant will not turn into a liquid, and therefore no cooling or heating will occur. Besides error codes registered by the system control unit, the improper working parameters caused by the impaired condenser function can lead to severe damage to the AC compressor.
Heat Condenser/ Internal Condenser
This heat exchanger supports the condenser function in the heat pump system and either removes or absorbs heat. It’s near the evaporator and, therefore, well protected by the dashboard, but make sure there is not something preventing the air from flowing through and that the air flaps controlling the airflow function properly.
Electric AC compressor
In the heat pump system of a battery-driven or hybrid car, is an HV electrical compressor, which is the heart of the system. It is therefore essential that these compressors are highly robust electrical motor-driven units based on scroll technology, with most having specific, non-conductive, lubricant requirements.
As with other electrical devices, the compressor’s functionality depends on the current signal, which technicians should also diagnose. Advanced troubleshooting utilising an oscilloscope is recommended, along with OBD and input signals inspection. The inner purity of the loop is also of crucial importance for the scroll-design compressor’s reliability.
NEVs will soon become commonplace in the aftermarket, so the ability of the independent sector to troubleshoot and fix their climate control systems and carry out routine maintenance will be vital for its future viability.
Nissens Automotive publishes a great deal of learning resources regarding NEV climate systems, including how to flush the heat pump loop or replace the HV AC compressor. It will continue with more NEV-related stories, all of which can be accessed, alongside many more technical articles, via its expert knowledge portal at: www.nissens.com/experts.