What are the symptoms of a clogged orifice tube?
Weak cooling and warm air from the vents are the most common signs of a clogged orifice tube.
In automotive A/C systems, the orifice tube meters liquid refrigerant to the evaporator. When it becomes blocked, the flow of refrigerant is restricted, causing pressure imbalances, reduced cooling, and potential stress on the compressor. The exact symptoms can vary with the severity of the blockage and the overall condition of the refrigerant and lubricants in the system.
Common symptoms to watch for
The following signs are frequently observed when the orifice tube is restricted. They help guide a diagnosis but may also point to other issues in the refrigeration loop.
- Weak or no cooling: The cabin doesn’t get cold, even with the proper refrigerant charge and settings.
- Warm air from the vents or inconsistent cooling: Air may feel cool only briefly or intermittently.
- Frost or icing on the evaporator or nearby lines: Abnormal moisture freezing at the evaporator can occur due to unusual refrigerant temperatures and flow.
- Abnormal or high side cycle and pressure readings: The high-pressure side may rise beyond normal ranges while the low-pressure side drops or fluctuates unexpectedly.
- Compressor symptoms such as unusual noise, heat, or rapid cycling: Inadequate refrigerant flow can stress lubrication and trigger odd compressor behavior.
- Uneven cooling or cold spots in the cabin: The evaporator may not receive a steady refrigerant flow, leading to inconsistent cooling across ducts.
These signs can appear individually or in combination. If several are present, a clogged orifice tube becomes a more likely suspect, though other problems (like leaks, contamination, or a failing expansion device) could produce similar symptoms.
Pressure readings and diagnostic clues
Pressure measurements from a manifold gauge set provide important context when evaluating a suspected clogged orifice tube. The following indicators help differentiate a clogged tube from other issues such as leaks or overcharges.
- High side pressure significantly higher than normal while the low side remains low or erratic: This pattern suggests restricted flow into the evaporator, consistent with a clogged metering device.
- Low side pressure lower than expected with reduced or irregular cooling: Flow restriction can starve the evaporator and depress the suction side.
- Temperature split between inlet and outlet of the evaporator not meeting expected values: The system isn’t transferring heat efficiently due to limited refrigerant entry to the evaporator.
Interpreting these readings alongside visual inspections and performance symptoms helps confirm whether the orifice tube is clogged. Because many A/C problems produce overlapping signs, professional diagnosis with the right tools is advised before any component replacement.
What to do next
If you suspect a clogged orifice tube, avoid DIY refrigerant charging or generic fixes. A qualified technician should perform a complete inspection, including pressure testing, leak detection, and possibly inspecting the orifice tube and evaporator core. Replacing a clogged orifice tube often requires recovering refrigerant, disassembling the dash or accessible A/C components, cleaning or replacing the evaporator, and recharging the system with the correct refrigerant and lubricant.
Summary
A clogged orifice tube typically presents with weak or warm cooling, unusual pressure readings, frost on the evaporator, and potential compressor stress. Diagnosis hinges on correlating symptoms with precise high- and low-pressure measurements and refrigerant analysis. Because signs overlap with other A/C problems, professional assessment is advised to confirm the cause and determine the proper repair, which may involve replacing the orifice tube and addressing any contamination or leaks in the system.
