Johnson Controls P128AA-2 Oil Control

The Johnson Controls P128AA-2 is a heavy-duty pressure-actuated lube oil protection switch designed to safeguard semi-hermetic compressors from lubrication failure. This oil pressure safety control monitors the net oil pressure—the difference between the oil pump discharge and the crankcase pressure. Featuring a manual reset mechanism and a 60-second time delay, this device bridges the gap during startup and temporary fluctuations, ensuring the compressor doesn't trip unnecessarily while providing a hard shutdown if oil pressure remains below the adjustable cut-out pressure difference of 8 to 70 PSI. Engineered for compatibility with all non-corrosive refrigerants, the P128AA-2 utilizes 1/4" SAE flare connectors without capillary tubing to minimize leak points and vibration fatigue. Capable of handling 120/240 VAC circuits, this HVAC compressor safety switch is essential for preventing catastrophic mechanical failure in commercial refrigeration and air conditioning systems.

• Adjustable Pressure Range: Field-adjustable differential from 8 to 70 PSI for precise system calibration.
• Time Delay Integration: Built-in 60-second thermal delay circuit prevents nuisance tripping during transient pressure dips.
• Universal Compatibility: Rated for use with all non-corrosive refrigerants across high, medium, and low-temp applications.
• Direct Connection: 1/4" SAE flare fittings provide a secure, leak-resistant interface without the need for capillary lines.
• Manual Reset Safety: Requires technician intervention after a trip to ensure the root cause of low oil pressure is addressed.

How do you wire the P128AA-2 for 240V versus 120V?
The control features a multi-tap transformer or terminal configuration. Always reference the internal wiring diagram to ensure the time delay heater receives the correct voltage to prevent burnout or timing inaccuracies.

Can this control be used with POE and PVE oils?
Yes, the internal bellows and brass fittings are compatible with standard mineral oils as well as synthetic POE and PVE lubricants commonly used in modern R-404A or R-448A systems.

What causes the manual reset to trip immediately after startup?
A trip usually indicates that the net oil pressure (pump outlet minus suction pressure) has not reached the setpoint within the 60-second window, often due to a clogged oil screen, worn pump, or refrigerant dilution in the oil.

Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.