In this article, we will explore the operation and failures of the stroke regulation or swash plate position valve in mechanically operated automotive piston compressors. This component, also known by its acronym POA (Ped Actuator), uses pilot technology to precisely control piston stroke according to the system’s demand.
Operation of the POA Valve
In older systems without a POA valve, compressors operated at full capacity whenever the clutch was engaged, depending solely on engine speed. This design had several drawbacks:
- Excessive or insufficient cooling: Poor temperature regulation that could lead to discomfort.
- Higher fuel consumption: The compressor ran continuously at maximum capacity, regardless of external temperature or user needs.
With the advent of variable displacement technology, modern compressors can mechanically adjust the piston stroke. This allows:
- Reduced refrigerant flow during low cooling demands, decreasing energy consumption.
- Increased cooling capacity during high thermal loads, such as hot days or heavy traffic.
This technology ensures a balance between comfort, energy efficiency, and system performance.
Symptoms of POA Valve Failure
Failures in the POA control valve are relatively common and may manifest through the following symptoms:
- Inconsistent cooling:
The air conditioner alternates between effective cooling and barely cooling or not cooling at all. - Failure at low speeds:
The system cools properly at high speeds but struggles in traffic or at low speeds. - Delayed cooling:
Cooling takes 10 to 20 minutes to begin but then functions correctly. - Poor performance on hot days:
The system cannot cool effectively during high thermal loads. - Abnormal system pressures:
The low-side pressure remains higher than normal, showing minimal reduction even when accelerating, while the high-side pressure appears within normal parameters.
Resolving POA Valve Failures
The good news is that, in most cases, replacing the compressor’s POA control valve is sufficient, eliminating the need to replace the entire compressor.
Recommended Repair Steps:
- Refrigerant recovery:
Before starting the replacement, extract and store the refrigerant from the system to prevent waste and contamination. - POA valve replacement:
In most models, the valve is externally accessible, making it easy to replace without removing the compressor. - System evacuation and recharge:
After replacing the valve, perform a full vacuum to remove moisture and recharge the system with the correct amount of refrigerant.- Avoid exposing the system to air for prolonged periods to prevent moisture ingress.
