Orifice
A fixed opening that meters refrigerant flow. In many residential AC and heat pump systems, the orifice (also called a fixed metering device or piston) sits at the inlet of the evaporator coil. Its precisely sized bore drops refrigerant pressure and controls how much liquid refrigerant enters the coil to boil off and absorb heat from your home. Unlike a thermostatic expansion valve, an orifice cannot adjust to changing load, so it relies on being the correct size for the equipment it serves.
💡 Key Takeaways
- ✓A fixed opening that meters refrigerant flow. In many residential AC and heat pump systems, the orifice (also called a fixed metering device or piston) sits at the inlet of the evaporator coil. Its precisely sized bore drops refrigerant pressure and controls how much liquid refrigerant enters the coil to boil off and absorb heat from your home. Unlike a thermostatic expansion valve, an orifice cannot adjust to changing load, so it relies on being the correct size for the equipment it serves.
- ✓An orifice has no moving parts, so its accuracy depends entirely on being sized correctly for your system.
- ✓A clogged orifice starves the coil and can look exactly like a low refrigerant charge.
- ✓Pistons are matched to tonnage, so they must be swapped when the equipment is replaced.
Orifice
/ˈɔːr.ə.fɪs/
Definition
A fixed opening that meters refrigerant flow. In many residential AC and heat pump systems, the orifice (also called a fixed metering device or piston) sits at the inlet of the evaporator coil. Its precisely sized bore drops refrigerant pressure and controls how much liquid refrigerant enters the coil to boil off and absorb heat from your home. Unlike a thermostatic expansion valve, an orifice cannot adjust to changing load, so it relies on being the correct size for the equipment it serves.
What does an orifice do in an air conditioner?
An orifice is a fixed opening that meters how much refrigerant flows into the evaporator coil. It drops pressure so the refrigerant can boil, absorb heat, and cool your home. Because it cannot adjust to load, it must be the correct size for the system.
Source: The Cooling Company
Quick Facts
Real-World Application
In a typical Las Vegas split system, a piston orifice is tucked inside the copper line at the indoor coil. If it clogs with debris or oil, the coil starves for refrigerant, pressures drop, and you feel weak, warm airflow on a 110 degree afternoon. A tech will often find low suction pressure and a frosted coil.
Pro Tip
If your air feels weak but the outdoor unit runs fine, ask your tech to inspect the orifice and filter drier before adding refrigerant. A clog mimics a low charge, and topping off will not fix it.
“If your air feels weak but the outdoor unit runs fine, ask your tech to inspect the orifice and filter drier before adding refrigerant. A clog mimics a low charge, and topping off will not fix it.”
Important Things to Keep in Mind
- An orifice has no moving parts, so its accuracy depends entirely on being sized correctly for your system.
- A clogged orifice starves the coil and can look exactly like a low refrigerant charge.
- Pistons are matched to tonnage, so they must be swapped when the equipment is replaced.
Did You Know?
Many piston orifices are stamped with a tiny number, like 55 or 63, that marks the bore size in thousandths of an inch. A change of just a few thousandths noticeably shifts how the whole system performs.
FAQ
How do I know if my orifice is clogged?
Signs include weak airflow, low suction pressure, and a frosted evaporator coil while the outdoor unit runs normally. A tech confirms it by measuring pressures and inspecting the metering device.
Is an orifice the same as a TXV?
No. An orifice is a fixed opening that cannot change with demand, while a thermostatic expansion valve adjusts refrigerant flow as conditions change. TXVs are more efficient but cost more to install.
Can I clean an orifice myself?
We do not recommend it. The system must be recovered, opened, and evacuated by a licensed tech, and the orifice is often replaced along with the filter drier to prevent repeat clogs.
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