Parts for your 2004 Toyota Mark x-Tx valve

2004 Toyota Mark X TX valve: what it does and when to service it

Based on technical references, the 2004 Toyota Mark X (GRX120/GRX121) is built with a thermal expansion valve (TX valve). Toyota’s Electronic Parts Catalogue for GRX120/121 lists a “Valve Sub-Assy, Cooler Expansion,” and the Toyota Repair Manual for Heating/Air Conditioning details removal and installation of the cooler expansion valve on the evaporator. DENSO service literature for Toyota passenger vehicles of this era also describes a TXV-type A/C system. So yes, this Mark X uses a TX valve, not an orifice tube.

The TX valve meters refrigerant into the evaporator, reacting to temperature and pressure to maintain the right superheat. That keeps the evaporator cold without icing, stabilises vent temps in stop–start traffic, and improves efficiency at different engine speeds. In day-to-day terms, it’s the bit that helps the air-con stay frosty on a scorcher without overworking the compressor.

It’s not a scheduled replacement item, but age, contamination, or moisture can make a TX valve stick or leak. Typical clues include:

• Cold then warm cycling, especially at idle or on hot days
• Evaporator icing or sweaty, weak airflow that won’t stay cold
• Abnormal high/low side readings on gauges, or a chattering compressor
• Oil/refrigerant stains at the valve or line joints

On the 2004 Mark X, the TX valve is mounted on the evaporator at the firewall side of the HVAC case. Access is from the passenger side, glovebox and lower trim usually come out, and some models need partial HVAC case access. Because the system must be recovered and evacuated, only a licensed air‑con technician should do the job (ARCtick in Australia, approved handlers in New Zealand).

Best practice when replacing the TX valve on a Mark X is to renew the O‑rings, insulate the sensing area as the manual specifies, replace or service the receiver/drier or desiccant (often part of the condenser assembly), pull a deep vacuum, then charge the exact mass of R‑134a shown on the under‑bonnet label. Use the compressor’s specified oil type and quantity (commonly DENSO ND‑OIL 8 for R‑134a systems—confirm on the compressor label or repair manual). If the old valve had debris, the system needs flushing and the cabin filter checked. Proper torque on fittings and a leak test (nitrogen/trace gas or UV dye) round out a tidy job.

Popular questions about 2004 Toyota Mark X TX valves

Does the 2004 Mark X use a TX valve or an orifice tube?
The 2004 Mark X uses a TX valve. Toyota’s EPC for GRX120/121 lists the cooler expansion valve as a service part, and the factory Repair Manual outlines the TXV removal/installation procedure. It’s a TXV-type DENSO system rather than a fixed orifice setup.

Where is the TX valve located on a 2004 Mark X?
It’s fixed to the evaporator at the firewall side of the HVAC case. Access is via the passenger footwell—glovebox and lower trims typically come off. Depending on trim and market spec, partial HVAC case access may be required, so allow time for careful disassembly and reassembly.

Do I need to replace the drier and re‑gas after changing the TX valve?
Yes. Once the system is opened, replacing the receiver/drier or desiccant bag is recommended to control moisture. The system must be evacuated and recharged by a licensed technician with the exact R‑134a charge mass and the correct oil type and quantity.