Four Seasons 74604 HVAC Heater Control Valve - Front

Four Seasons 74604 Heater Valve

Four Seasons 74604 is a vacuum open, non-bypass HVAC heater control valve built with a steel body and OE replacement fitment. It uses two hose connectors and a 5/8 in. opening size, making it a direct service part for classic heating systems that rely on vacuum-operated coolant flow control.

Key Features

• Vacuum-operated heater valve with non-bypass design
• Steel construction for HVAC service applications
• Two hose connectors
• 0.625 in. / 15.875 mm opening size
• OE replacement part for factory-style service
• Four Seasons Heater Valve line for temperature control components

Product Details

This Four Seasons heater valve is used to regulate coolant flow through the heater core in vehicles equipped with vacuum-controlled heating systems. The vacuum open, non-bypass design supports factory-style operation in applications such as Jaguar XJ6, Jaguar XJ12, Jaguar XJS, Buick Skylark, Pontiac GTO, Pontiac Firebird, and Cadillac DeVille. Part number 74604 is also cross-referenced with Hayden 5918 for the same application.

As part of the Four Seasons Heater Valve line, this component is intended for temperature control service where original-style hose routing and vacuum actuation are required. The 5/8 in. port size and steel construction make it a practical replacement for aging heater control valves on classic GM and Jaguar HVAC systems.

Common Problems This Part Can Address

• No heat from the cabin heater due to restricted coolant flow
• Heater core flow control issues caused by a failed vacuum valve
• Coolant leakage at the heater control valve body
• Stuck-open or stuck-closed heater valve operation
• Loss of factory heater temperature control in vacuum-operated systems

Installation Notes and Tips

• Verify vacuum operation before installation to confirm the valve opens and closes correctly.
• Match the 0.625 in. hose opening size to the existing heater hoses and fittings.
• Confirm whether the vehicle uses a non-bypass heater valve before ordering.
• Check fitment details for specific applications such as 1968 Chevrolet Camaro, 1969 Buick LeSabre, and 1975-1976 Jaguar XJ6.
• Inspect hose condition and clamp sealing surfaces during replacement to help prevent leaks.

Quality Assurance

Four Seasons 74604 is an OE replacement heater valve built for HVAC temperature control service. It is listed across multiple interchange references and direct-fit applications, including 1963-1970 Cadillac DeVille, 1965-1972 Pontiac GTO, and 1972-1976 Jaguar XJ6, supporting accurate parts matching for classic vehicle repair.