Home › Troubleshooting › Stuck metering device
What happens when the expansion valve sticks?
The metering device controls exactly how much refrigerant sprays into the evaporator. Stuck restricted, it starves the coil and freezes it — mimicking a low charge almost perfectly. Stuck open, it floods liquid straight through to the compressor, which is built to pump gas, not liquid, and can be destroyed by the slugging.
What causes it
Debris, moisture freezing inside it, or a failed sensing bulb on the expansion valve.
What it does to the cycle
Stuck closed/restricted, it starves the evaporator (which then freezes, just like low charge). Stuck open, it floods too much liquid through, which slugs back and can wreck the compressor.
What you'd notice
Poor cooling, frost showing up in odd spots, and unusual compressor noise.
What to do about it
- Know that the symptoms mimic low refrigerant. Don't let anyone simply add refrigerant to 'see if it helps'.
- Ask the tech to compare superheat and subcooling readings — that pairing is what separates a TXV fault from an actual leak.
- Expect the filter-drier to be replaced too; debris or moisture is usually what fouled the valve.
- Valve replacement means recovering and recharging the refrigerant, so it's a half-day job, not a quick swap.
- If liquid has been slugging back, have the compressor evaluated at the same time.
The bottom line
Needs a technician to diagnose and replace the valve and clear whatever fouled it.