Parts for your 2018 Nissan Serena-Tx valve

2018 Nissan Serena TX-Valve: What It Does and How to Look After It

For the 2018 Nissan Serena (C27 series), a TX-valve (thermal expansion valve) is indeed used in the air-con system. This is documented in the Nissan Electronic Service Manual for the C27 (Heater & Air Conditioning section), which illustrates an expansion valve at the front evaporator and, on dual A/C models, a second valve at the rear unit. Nissan’s FAST electronic parts catalogue also lists “Expansion Valve Assy (Front)” and “Expansion Valve Assy (Rear)” for C27 Serena variants with rear coolers. Major aftermarket catalogues from OEM suppliers (e.g., DENSO) equally specify compatible expansion valves for the 2016–2020 Serena range.

Because the Serena runs a TX-valve set-up, the valve’s job is to meter refrigerant into the evaporator based on temperature and pressure, maintaining correct superheat. That keeps the evaporator cold without flooding it, stabilises vent temps, and protects the compressor from liquid slugging. On Serena models with rear air-con, there’s a second TX-valve doing the same job at the rear evaporator, so both ends get consistent cooling for passengers in every row.

This little metering device isn’t a routine replacement item, but it does rely on a clean, well-charged system. During an air-con service, a tech should check for stable low/high-side pressures, even vent temps, and no frosting on the suction line near the valve. If the air-con cycles hot–cold, struggles at idle or high speed, or shows abnormal pressure readings, the TX-valve may be sticking or restricted.

• Typical signs of TX-valve trouble: weak cooling, fluctuating vent temps, line frosting or sweating at the valve, hissing, and pressure readings that don’t match spec.
• Best practice on replacement: recover the refrigerant, replace the receiver-drier, fit new O-rings, torque fittings to spec, evacuate and recharge by weight, and leak-test. If debris is found, flush the system and consider replacing both front and rear valves on dual A/C models.
• Helpful maintenance tips: keep the cabin filter fresh to maintain airflow across the evaporator, follow the under-bonnet label for the correct refrigerant and oil type, and avoid stop-leak products that can foul the valve.

Access-wise, the front TX-valve lives at the evaporator inlet (behind the dash area), while the rear valve is mounted near the rear evaporator assembly. A competent air-con specialist will have the Serena back blowing icy air without drama, provided the system’s kept clean and properly charged.

Popular questions about the 2018 Nissan Serena TX-valve

Does the 2018 Serena have one or two TX-valves?
Most New Zealand and Australian-delivered Serenas with rear air-con have two: one at the front evaporator and one at the rear. Base variants without rear cooling typically have a single front TX-valve.

How can they tell a bad TX-valve from low refrigerant?
Low gas usually gives poor cooling across the board and low static pressure. A sticky TX-valve can show normal charge but erratic pressures, line frosting at the valve, and vent temps that swing hot–cold. Proper gauge readings and temperature checks make the call clear.

Can a TX-valve be cleaned, or does it need replacing?
If contamination is minor, flushing the system may help, but TX-valves are generally replaced. If debris is present, replace the receiver-drier and investigate the cause (e.g., compressor wear) to avoid repeat issues.