Parts for your 1998 Daihatsu Gran move-Tx valve

1998 Daihatsu Gran Move TX valve (thermostatic expansion valve): what it is and how to look after it

Yes, the 1998 Daihatsu Gran Move uses a TX valve in its air‑conditioning system. This is supported by Daihatsu’s Gran Move/Pyzar (G300 series) workshop manual HVAC section identifying a thermostatic expansion valve at the evaporator inlet, the Daihatsu Electronic Parts Catalogue (A/C group) listing “Valve, Expansion” for G300‑series Gran Move models, and Denso’s aftermarket catalogue carrying an A/C expansion valve for the same vehicle range.

On the Gran Move, the TX valve’s job is to meter R134a into the evaporator based on the temperature at the outlet of the core. By maintaining correct superheat, it helps the evaporator run cold without icing, keeps fuel use sensible, and delivers steady cabin temps even as driving conditions change. When the TX valve sticks or drifts out of spec, drivers often notice weak cooling at idle, intermittent bursts of chill followed by warm air, or frost on the evaporator/lines.

Servicing advice for this model is straightforward. If cooling performance is off, a tech should check high/low side pressures and evaporator outlet temperature, then verify that airflow is good (clean condenser, radiator, and—if fitted—cabin filter). Because the Gran Move uses a TXV system rather than a fixed orifice, odd pressure behaviour (very low low‑side with a frosty line, or hunting pressures) can point to the valve.

Replacement needs an ARCtick‑licensed technician (AU) or a licensed handler (NZ). They’ll recover the refrigerant, access the TX valve at the evaporator inlet (typically behind the glovebox/evaporator cover area), replace the valve and all O‑rings with HNBR items, and add the correct amount of PAG oil for the component change. Best practice is to replace the receiver‑drier whenever the system is opened, then nitrogen‑pressure test, deep‑vacuum the system, and recharge by weight to the value on the under‑bonnet label. Afterward, they’ll confirm vent temps, superheat, and that there’s no frosting or compressor chatter.

Keen owners can help the TX valve live a long life by keeping the condenser clean, running the A/C regularly year‑round to circulate oil, and sorting any refrigerant leaks early so the valve isn’t starved of oil and debris‑contaminated.

• Common signs of a crook TX valve: poor cooling at idle, evaporator icing, hissing at the firewall, and unstable gauge readings.
• Always use new O‑rings and the correct oil, torque fasteners to the workshop manual spec.

FAQ 1: Where is the TX valve on a 1998 Daihatsu Gran Move?
It’s mounted at the evaporator inlet, typically accessed by removing the glovebox and the evaporator/airbox cover. The refrigerant lines pass through the firewall to this location. A tech can confirm the exact access steps from the Daihatsu workshop manual for the G300 series.

FAQ 2: How do I tell a failing TX valve from low refrigerant?
Low refrigerant usually gives steadily warmish air and both gauge pressures reading low. A faulty TX valve can show a very low, icing low‑side with a normal or high high‑side, pulsing or hunting pressures, and temperature swings at the vents. Proper diagnosis with gauges and temperature probes makes the call clear‑cut.

FAQ 3: Do I need to change the receiver‑drier when replacing the TX valve?
Yes—industry best practice is to fit a new receiver‑drier any time the system is opened. It captures moisture and debris that would otherwise shorten the life of the new TX valve and the compressor.