Four Seasons 91605 HVAC Heater Core

Four Seasons 91605 Heater Core Overview

The Four Seasons 91605 heater core is a copper/brass HVAC heater core built for direct replacement service in heating and defrost systems. With a 7-3/4 in. height, 7-1/2 in. width, and 1-7/8 in. depth, it is sized for applications that require a compact copper core with 5/8 in. inlet and outlet tubes.

Four Seasons Heater Core line parts are focused on OE-style replacement fit and construction. This heater core meets or exceeds OEM requirements and uses a copper core material for dependable heat transfer in the HVAC system.

Key Features

• Part number 91605 heater core for HVAC repair and replacement
• Copper/brass heater core style with copper core material
• Core dimensions: 7-3/4 in. height, 7-1/2 in. width, 1-7/8 in. depth
• 5/8 in. tube connections on both inlet and outlet
• Meets or exceeds OEM specifications
• Four Seasons Heater Core product line

Detailed Product Description

The Four Seasons 91605 is an HVAC heater core designed for vehicles that use a copper/brass core layout and 5/8 in. tube connections. Its compact 7.750 in. x 7.500 in. x 1.875 in. dimensions make it a practical replacement for heating systems where core size and tube placement must match the original unit. This part number 91605 is a direct-fit style replacement for service work on vehicles such as Chevrolet C/K and GMC Sierra applications when the original heater core matches these specifications.

As part of the Four Seasons Heater Core line, this unit is built for OE-style replacement needs in the HVAC system. It is a copper heater core with no adjustable pipe positioning, so correct application matching is important before installation. This part cross-references Nissens 94605 for the same application.

What This Heater Core Helps Address

• Weak or inconsistent cabin heat
• Coolant odor inside the vehicle
• Coolant seepage from the HVAC case area
• Restricted heat output caused by a clogged core
• Temperature imbalance between defrost and floor heat functions

Installation Notes and Tips

Verify core height, width, depth, and 5/8 in. tube size against the original heater core before installation. Because adjustable pipe positioning is not included, the inlet and outlet orientation must match the vehicle’s HVAC case layout. Flush the cooling system and inspect hoses, clamps, and the heater control valve, if equipped, before installing the replacement core. For fitment-based searches, this part is commonly referenced for Chevrolet C/K and GMC Sierra heater core replacement needs when the original dimensions align with the 91605 specification.

Quality Assurance

Four Seasons lists this heater core as meeting or exceeding OEM requirements, supporting OE-style replacement expectations for HVAC service. The copper/brass construction and application-specific sizing are intended to align with original equipment standards for the correct vehicle fit.