Four Seasons 74618 HVAC Heater Control Valve

Four Seasons 74618 Heater Control Valve

Four Seasons 74618 is an OE replacement HVAC heater control valve for vacuum-operated heating systems. It uses a non-bypass, vacuum-closing design with three hose connectors to regulate coolant flow through the heater circuit and support consistent cabin temperature control.

Key Features

• Vacuum-operated heater valve for HVAC temperature control
• Non-bypass style with bypass function
• Plastic construction for OE-style replacement use
• Three hose connectors for the specified heater hose routing
• Opening sizes: 0.625 in. (15.875 mm) and 0.500 in. (12.700 mm)
• Direct replacement part number 74618 for listed applications

Product Details

This Four Seasons Heater Valve line component is built for vehicles that use vacuum control to open and close coolant flow through the heater core circuit. The non-bypass configuration helps maintain proper HVAC operation in systems that require coolant shutoff rather than continuous bypass flow. Four Seasons 74618 is an OE replacement heater control valve for 2002-2006 Chevrolet Trailblazer, 2002-2006 Chevrolet Trailblazer EXT, 2002-2005 GMC Envoy, 2004-2005 GMC Envoy XUV, 2002-2006 GMC Envoy XL, and 2003-2008 Isuzu Ascender.

This part cross-references UAC HV1211C for the same application.

Common Repair Symptoms

• Heater output stuck on hot or cold
• Coolant flow not responding to HVAC temperature changes
• Vacuum-controlled heater valve not opening or closing correctly
• Cabin heat that does not match the selected temperature setting
• Leaking or cracked heater valve housing

Installation Notes

Verify hose diameter, connector count, and vacuum routing before installation. Match the valve style to the original non-bypass configuration and confirm the openings align with the vehicle’s heater hose sizes. For best results, inspect adjacent hoses and vacuum lines for wear before replacing the valve.

Quality Assurance

Four Seasons supplies OE replacement HVAC components, and this heater valve is built to match the listed application requirements for fit and function.