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Refrigerant selection is an important technical decision in bus air conditioning systems. It affects cooling performance, system design, maintenance requirements, environmental compliance and long-term operating costs.
As emission regulations become stricter and high-temperature operation becomes more common in many regions, bus OEMs and fleet operators need to evaluate which refrigerants are suitable for different vehicle types, HVAC architectures and market requirements.
TCHAIN Taichang compares three refrigerants used across its diesel and electric bus air conditioning systems: R134a, R407C and R410A.
Most bus air conditioning systems use a vapor compression refrigeration cycle. The process includes four main stages:
Compression: The compressor increases the pressure and temperature of the gaseous refrigerant.
Condensation: The refrigerant passes through the condenser, releases heat outside the vehicle and changes into liquid form.
Expansion: The liquid refrigerant moves through the expansion valve, where pressure drops and the refrigerant becomes a low-temperature mixture.
Evaporation: The refrigerant absorbs heat inside the evaporator and vaporizes, cooling the passenger compartment.
This cycle is used across rooftop, built-in and electric bus air conditioning systems.
Two indicators are commonly used to evaluate refrigerants:
ODP, Ozone Depletion Potential: Measures the impact of a refrigerant on the ozone layer. Modern bus air conditioning refrigerants generally have an ODP of 0.
GWP, Global Warming Potential: Measures the greenhouse effect of a refrigerant over a defined period, usually 100 years. Lower GWP values are increasingly important as global and regional regulations restrict high-GWP refrigerants.
R134a is widely used in traditional diesel bus air conditioning systems. It has mature system compatibility, broad service availability and relatively low maintenance cost.
In TCHAIN’s product range, R134a is used in TCH diesel air conditioners and TCN built-in air conditioners for fuel buses, covering applications such as coaches, school buses and special vehicles from 5 to 14 metres.
Its main limitation is environmental compliance. Although R134a has an ODP of 0, its GWP is above 1000, which has led to restrictions in several markets for newly launched vehicles.
R407C is a mixed refrigerant previously used in some small new energy bus air conditioning applications. It offers strong cooling capacity and can be suitable for older system designs or specific retrofit projects.
TCHAIN applies R407C in the TCD07A air conditioner for 6 to 7 metre small electric buses.
However, R407C also has a high GWP and is gradually becoming less suitable for markets with stricter environmental requirements.
R410A is used in TCHAIN’s new energy bus air conditioning systems. It supports cooling and heating configurations, including single cooling, PTC heating, heat pump operation and combined thermal solutions.
In TCHAIN’s portfolio, R410A is used in TCD07D, TCD08D, TD40A and TCD12D systems for 6 to 12 metre pure electric buses. These systems are designed for high-voltage vehicle power supply in the DC420 to DC720V range.
Compared with R134a, R410A operates at higher pressure, which means installation and maintenance must be carried out by trained technicians using appropriate tools and procedures.
RefrigerantODPGWPTypical TCHAIN ApplicationMain Vehicle TypeR134a01000+TCH diesel air conditioners, TCN built-in fuel bus air conditionersDiesel buses, coaches, school busesR407C01000+TCD07A small electric bus air conditionerEarly small electric bus projectsR410A0Medium to highTCD new energy bus air conditionersPure electric urban buses
Different refrigerants should not be mixed. Mixing refrigerants can damage compressors, block pipelines and create system safety risks.
Refrigerant recovery, replacement and filling should be carried out by certified maintenance technicians using suitable service equipment. The correct refrigerant type and filling amount must follow the confirmed technical specification of the air conditioning system.
For OEMs and fleet operators, refrigerant selection should be based on the vehicle powertrain, target market, operating climate, service network and local environmental regulations.
For diesel buses, mature refrigerants such as R134a may still be relevant in some markets due to service availability and cost. For electric buses, refrigerant selection must also consider high-voltage integration, heat pump performance and thermal management requirements.
As regulations continue to move toward lower-emission technologies, bus HVAC suppliers are expected to develop systems that balance cooling performance, heating efficiency, maintenance safety and environmental compliance.
For OEMs, bodybuilders and fleet operators, refrigerant strategy is becoming part of the wider vehicle design and lifecycle cost discussion.
