Four Seasons 91509 HVAC Heater Core

Four Seasons 91509 Heater Core Overview

The Four Seasons 91509 heater core is a copper/brass HVAC heater core built to meet or exceed OEM requirements. With a copper core material and compact dimensions of 7-3/4 in. height, 6 in. width, and 1-7/8 in. depth, it is specified for select Cadillac, Chevrolet, Oldsmobile, and Pontiac applications.

This Four Seasons heater core is part of the Heater Core product line and is engineered for direct replacement service in vehicles equipped with air conditioning where noted. It cross-references APDI 9010059 for the same application.

Key Features

• Part number: 91509
• Copper/brass heater core construction
• Copper core material for heat transfer performance
• Meets or exceeds OEM specifications
• Core dimensions: 7-3/4 in. height, 6 in. width, 1-7/8 in. depth
• Tube sizes: 0.625 in. and 0.750 in.
• Fixed pipe positioning; adjustable pipe positioning: No

Detailed Description

Four Seasons 91509 is an HVAC heater core designed for heating system repair where the original core has leaked, restricted flow, or lost heat output. The copper/brass design supports efficient coolant-to-air heat transfer, while the listed dimensions and tube sizes help confirm proper fit during replacement. This part number is used in 1976-1979 Cadillac Seville, 1976-1979 Chevrolet Nova, 1976-1979 Oldsmobile Omega, and 1977-1979 Pontiac Phoenix applications, including Chevrolet Nova and Oldsmobile Omega vehicles equipped with air conditioning.

As a Four Seasons Heater Core product, 91509 is positioned as an OE-style replacement for service work that requires accurate dimensions and confirmed vehicle coverage. Use the part number 91509 when matching the heater core to the original unit and verifying the inlet and outlet tube configuration.

What This Heater Core Helps Address

• Loss of cabin heat from a leaking or restricted heater core
• Coolant odor or moisture inside the HVAC case area
• Uneven or weak defrost performance caused by poor heater output
• Temperature control issues related to reduced coolant flow through the core
• Replacement needs on 1976-1979 Cadillac Seville, Chevrolet Nova, Oldsmobile Omega, and Pontiac Phoenix models

Installation Notes and Tips

Confirm the original heater core dimensions, tube diameters, and pipe orientation before installation. This unit has no adjustable pipe positioning, so alignment with the factory HVAC case and hose routing should be checked carefully. On Chevrolet Nova and Oldsmobile Omega applications, verify whether the vehicle is equipped with air conditioning, as noted in the fitment data. Always inspect the cooling system, hoses, and clamps before installing the new core.

Quality Assurance

Four Seasons lists this heater core as meeting or exceeding OEM requirements, supporting a direct-replacement approach for service technicians and DIY repairs. The copper/brass construction and application-specific fitment data provide a reliable basis for selecting the correct HVAC heater core for the listed Cadillac Seville, Chevrolet Nova, Oldsmobile Omega, and Pontiac Phoenix vehicles.