Four Seasons 36573 A/C Trinary Switch

Four Seasons 36573 Trinary Pressure Switch

The Four Seasons Pressure Switch 36573 is a system-mounted A/C trinary switch built for 12-volt HVAC systems. It monitors refrigerant pressure and helps control compressor and fan operation in select BMW applications, including BMW 840Ci, 850Ci, 850CSi, 850i, 318i, 318is, 318ti, 325i, 325is, and M3 models.

Built with a steel body, gray rectangular female connector, and 4-pin Weather Pack design, this trinary pressure switch meets or exceeds OEM requirements and uses a 7/16" x 20 female fitting thread.

Key Features

• System-mounted trinary pressure switch for automotive A/C control
• 12-volt electrical design with 4 terminals and pin-style connection
• Rectangular female connector in gray with Weather Pack sealing
• Steel construction for HVAC system durability
• Pressure operating points: low on 30 psi, low off 28 psi, medium on 240 psi, medium off 200 psi, high on 350 psi, high off 455 psi
• Meets or exceeds OEM specifications
• Four Seasons 36573 cross-references AP Exhaust 50024 for the same application

Detailed Description

Four Seasons 36573 is a trinary A/C pressure switch used in HVAC systems that require pressure-based compressor protection and fan control. The switch is designed to respond to low, medium, and high refrigerant pressure thresholds, helping the system manage compressor cycling and condenser fan operation. This makes it a direct-fit service part for select BMW 840Ci and BMW 850Ci applications, along with BMW 318i, 318is, 318ti, 325i, 325is, and M3 models listed in the fitment data. The Four Seasons Pressure Switch line focuses on replacement components for automotive climate control systems, and this part follows that approach with OE-style electrical and mounting specifications.

What It Helps Address

• A/C compressor not engaging due to pressure switch failure
• Compressor cycling caused by incorrect refrigerant pressure signal
• Condenser fan control issues tied to trinary switch operation
• HVAC system shutdown from open or failed pressure switch contacts
• Intermittent air conditioning performance in BMW 840Ci, 850Ci, 318i, 325i, and M3 applications

Installation Notes and Tips

• Verify the 7/16" x 20 female thread and rectangular female connector before installation.
• Confirm the vehicle uses a system-mounted trinary pressure switch with a 4-terminal Weather Pack connection.
• Inspect the A/C system for proper refrigerant charge and pressure before replacing the switch.
• Match the electrical connector and terminal layout to the original part to avoid wiring mismatch.
• Use the vehicle-specific fitment notes, including 1995 BMW models with the listed to-1/95 coverage, to confirm application.

Quality Assurance

Four Seasons 36573 is engineered to meet or exceed OEM requirements for pressure-switch function and fit. It is built as a replacement HVAC control component for select BMW models from 1991 through 1997, including BMW 840Ci, 850Ci, 850CSi, 850i, 318i, 318is, 318ti, 325i, 325is, and M3 applications.