Parts for your 2018 Toyota Mark x-Tx valve

2018 Toyota Mark X TX valve — what it does and how to look after it

Yes, the 2018 Toyota Mark X runs a TX valve (thermal expansion valve) in its air-con system. Technical references include the Toyota Repair Manual for the GRX13# platform and the Toyota Electronic Parts Catalogue, which list a “Valve, Expansion (for Cooler Unit)” at the evaporator inlet. The Mark X uses a DENSO HVAC layout that relies on a TX valve rather than an orifice tube, so the part is very much relevant to this model.

The TX valve meters refrigerant into the evaporator based on temperature and pressure, keeping superheat in the sweet spot. That means colder air at the vents, stable cabin temps, and good compressor protection. When it’s healthy, the system cools briskly at idle and on the move without frosting up or cycling oddly.

It’s not a routine service item, but a crook TX valve can show up after moisture or debris gets into the system, or simply with age. Telltales include weak cooling at idle or at highway speeds, vent temps that swing hot–cold, frost or sweating on lines near the firewall, a constant hiss at the expansion block, or odd gauge readings (high high-side with starved low-side, or vice versa). If the system’s been open to atmosphere or the compressor’s let go, the valve is a prime suspect for replacement along with the desiccant.

• Best-practice replacement: recover refrigerant, remove the valve at the evaporator, fit new O-rings, and renew the receiver/drier or desiccant bag (the Mark X uses a condenser-integrated receiver). Evacuate to a deep vacuum, add the correct PAG oil amount, recharge to the specified mass, then leak-test and verify vent temps and pressure balance.
• Tips that help: always use the refrigerant and oil called out on the vehicle label, torque fittings to Toyota spec, and keep the cabin filter fresh so the evaporator won’t ice up and stress the valve.

Because handling refrigerant is regulated in Australia and New Zealand, this job should be carried out by a licensed air-con technician. Done properly, a new TX valve restores crisp, consistent cooling and helps the Mark X’s DENSO system run quietly and efficiently for the long haul.

Popular questions about the 2018 Toyota Mark X TX valve

Does the 2018 Toyota Mark X actually have a TX valve?
Yes. Toyota’s service literature for the GRX13# series and the parts catalogue both list an expansion valve fitted at the evaporator. The Mark X’s DENSO air-con system is designed around a TX valve rather than an orifice tube.

When should the TX valve be replaced on a Mark X?
It’s replaced when there are symptoms like unstable vent temps, frost at the evaporator inlet, or abnormal pressure readings, or any time the system has been contaminated (for example after a compressor failure) or left open to air. It isn’t a scheduled maintenance item.

Can a faulty TX valve damage the compressor?
Indirectly, yes. If the valve sticks shut, the compressor can be starved of refrigerant flow and oil return, if it overfeeds, liquid can return to the compressor. Either scenario can shorten compressor life, so diagnosing and sorting a dodgy valve early is a good move.