Parts for your 2017 Toyota Mark x-Tx valve

2017 Toyota Mark X TX‑Valve: fitted, what it does, and how to look after it

Based on Toyota’s own service documentation and parts listings, the 2017 Toyota Mark X (GRX130/GRX133) is built with a thermal expansion valve (TX‑valve). Toyota’s Repair Manual for the GRX130 series includes a “Cooler Expansion Valve” component in the refrigerant circuit, and the Toyota Electronic Parts Catalogue lists a “Valve Assy, Cooler Expansion” for 2017 Mark X variants. DENSO HVAC service information for Toyota passenger vehicles of this era also shows a block‑type TXV at the evaporator inlet. So yes—this model uses a TX‑valve, and it’s very much relevant to A/C performance.

The TX‑valve meters refrigerant into the evaporator, regulating flow to keep evaporator superheat in the sweet spot. That’s how the Mark X’s auto climate control can deliver steady, cold air without freezing the core or flooding the compressor. When the valve sticks, leaks, or goes out of calibration, cooling suffers—often showing up as poor cooling at idle, frosty lines near the firewall, or wildly fluctuating vent temps.

On this Toyota, the TX‑valve lives at the evaporator (in the HVAC case behind the dash). It’s not a routine service item, but it’s commonly replaced when the system’s been contaminated (e.g., after a compressor failure) or when diagnostics point squarely at the valve. If opening the system, best practice is to replace the necessary O‑rings, renew the desiccant (the Mark X uses a condenser with an integrated drier/desiccant bag), evacuate properly, and recharge with the refrigerant shown on the under‑bonnet label (typically R134a for this model year). Match oil type and quantity to Toyota specs, especially if other components have been changed.

• Typical tell‑tales of a crook TX‑valve: uneven cooling, frost on the evaporator inlet, low side pressure abnormally low or hunting, and a hissing that never quite settles.
• Replacement tips: use OEM or quality DENSO‑equivalent valves, new O‑rings lightly oiled, and torque fittings to the service manual spec. Always nitrogen‑pressure test, then deep vacuum and leak check before charging.
• If the A/C’s been open to atmosphere or the compressor grenaded, budget for a valve, desiccant service, thorough flushing (where applicable), and a fresh cabin filter so airflow stays spot on.

Get the TX‑valve right and the Mark X’s cabin stays cool across Auckland traffic or a scorching arvo on the Hume—no fuss, no icy surprises.

Where is the TX‑valve on a 2017 Mark X?

It’s mounted at the evaporator inlet inside the HVAC case (behind the dash). Access typically requires dash/HVAC case work, which is why it’s often tackled alongside other A/C jobs to save on labour.

Does the TX‑valve need regular servicing?

No routine servicing is required. It’s inspected/diagnosed if cooling performance drops or the system has been opened. If contamination is suspected—say after a compressor failure—replacing the valve and servicing the desiccant is smart preventative maintenance.

Should the TX‑valve be replaced when the compressor is changed?

It’s not mandatory, but it’s recommended if metal debris or sludge is present. Pairing a new compressor with a clean metering device and fresh desiccant helps protect the new unit and restores stable pressures and temps.