Four Seasons 20991 A/C Trinary Switch

Four Seasons 20991 A/C Trinary Pressure Switch

The Four Seasons Pressure Switch line includes this system-mounted trinary pressure switch for HVAC A/C clutch and compressor control. Part number 20991 is a 12-volt, 4-terminal switch with a male connector and male M11 x 1.00 fitting, built in steel and specified with Weather Pack protection.

Compatible With Lexus RX300, Mitsubishi Galant, and Mitsubishi Mirage applications, this Four Seasons 20991 switch is used in A/C systems that need pressure-based control for compressor and fan operation. It meets or exceeds OEM requirements and is set up as an open-style trinary pressure switch for system-mounted installation.

Key Features

• Four Seasons Pressure Switch line, part number 20991
• Trinary A/C pressure switch for HVAC compressor and fan control
• 12-volt electrical design with 4 pin terminals
• Male connector and male fitting with M11 x 1.00 thread size
• Steel construction with Weather Pack protection
• System-mounted layout that meets or exceeds OEM specifications
• Pressure operating points: low on 30 psi, low off 29 psi, medium on 250 psi, medium off 210 psi, high on 350 psi, high off 455 psi

Detailed Description

The Four Seasons 20991 trinary pressure switch monitors refrigerant pressure and helps manage A/C clutch engagement and condenser fan operation through defined low, medium, and high pressure thresholds. This pressure switch is a direct-fit style component for select Lexus RX300, Mitsubishi Galant, and Mitsubishi Mirage vehicles, making it a practical choice when replacing a failed HVAC pressure control switch in the original system-mounted location. The Four Seasons 20991 part number is commonly searched for A/C clutch and compressor service, especially when diagnosing pressure-related cycling or fan control concerns.

This Four Seasons Pressure Switch product line is built for automotive HVAC service where accurate pressure signaling matters. The open/open configuration, pin terminals, and Weather Pack connection support clean integration into the vehicle’s A/C electrical circuit.

Common Problems This Part Can Address

• A/C compressor not engaging due to pressure switch failure
• Condenser fan control issues tied to refrigerant pressure sensing
• Intermittent A/C cycling caused by worn switch contacts
• HVAC system shutdown from incorrect high- or low-pressure readings
• Fault codes or drivability complaints related to A/C pressure control

Installation Notes and Tips

Verify the original switch connector style, terminal count, and M11 x 1.00 thread before installation. Because this is a system-mounted trinary pressure switch, confirm refrigerant pressure is properly recovered and the A/C circuit is inspected for leaks or wiring damage before replacing the part. For fitment, this part fits 1999-2003 Lexus RX300, 1994-1998 Mitsubishi Galant, and 1991-1992 Mitsubishi Mirage.

Quality Assurance

Four Seasons 20991 meets or exceeds OEM requirements and is built to the specified electrical and mechanical dimensions for the listed applications. This part cross-references Continental 50029 for the same application.