Four Seasons 74781 HVAC Heater Control Valve

Four Seasons 74781 Heater Valve Overview

Four Seasons 74781 is an OE replacement HVAC heater control valve built for vacuum-operated heater circuits with bypass function. It uses a plastic body, four hose connectors, and a vacuum-close bypass design to regulate coolant flow through the heater system on select Chevrolet and GMC trucks and vans.

As part of the Four Seasons Heater Valve line, this valve is focused on direct-fit temperature control service for vehicles that use a bypass-style heater valve. It is a practical replacement for worn or leaking valves on applications such as Chevrolet Express, GMC Savana, Silverado, Sierra, Tahoe, and Yukon models.

Key Features

• Part number 74781 HVAC heater control valve
• Vacuum-operated, bypass-style valve
• Vacuum closes bypass heater valve
• OE replacement design
• Plastic construction
• Four hose connectors
• Opening sizes: 0.625 in (15.875 mm), 0.750 in (19.050 mm)

Detailed Product Description

Four Seasons 74781 is designed for HVAC temperature control systems that rely on vacuum actuation to manage heater coolant flow. The bypass configuration helps route coolant through the heater circuit as required by the vehicle’s climate control system, making it a direct-service replacement for many GM applications. This part number 74781 is commonly referenced for Chevrolet Express and GMC Savana vans, as well as Chevrolet Silverado, GMC Sierra, Tahoe, Yukon, and related full-size truck and SUV platforms.

This part cross-references Monroe Shocks & Struts 5930 for the same application.

What This Heater Valve Helps Address

• Heater output stuck on or stuck off
• Coolant flow control issues in the heater circuit
• Vacuum-actuated valve failure
• Leaking or cracked heater valve housing
• Temperature control problems in the cabin HVAC system

Installation Notes and Fitment

Compatible With 2011-2019 Chevrolet Express 2500, N/A; 2011-2019 Chevrolet Express 3500, N/A; 2013-2019 GMC Savana 2500, N/A; 2013-2019 GMC Savana 3500, N/A; 2011-2012 Chevrolet Express 1500, N/A; 1997-2012 GMC Savana 1500, N/A, 4 Ports; Heater Valve; 1997-2012 GMC Savana 2500, N/A, 4 Ports; Heater Valve; 1997-2012 GMC Savana 3500, N/A, 4 Ports; Heater Valve; 1997-2010 Chevrolet Express 1500, N/A, 4 Port; Heater Valve; 1997-2010 Chevrolet Express 2500, N/A, 4 Port; Heater Valve; 1997-2010 Chevrolet Express 3500, N/A, 4 Port; Heater Valve.

Additional compatible applications include 1999-2000 Chevrolet Silverado 1500, N/A; 1999-2000 GMC Sierra 1500, N/A; 1995-2000 Chevrolet Tahoe, N/A; and 1995-2000 GMC Yukon, N/A. Verify hose routing, connector count, opening sizes, and vacuum operation against the original valve before installation. This part number 74781 is also listed for 1995-2000 Chevrolet and GMC full-size truck and SUV applications, including C/K-series and Suburban models, where the vehicle uses the matching heater valve configuration.

Quality Assurance

Four Seasons heater valves are cataloged as OE replacement components for HVAC service, with application-specific fitment data used to match the original valve style and operation.