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Heater Rebuild 101

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Click Here For Photos of Actual '66 Heater Rebuild

In most cases, forty year old seals, paper defroster plenums, cones and ducting have earned their retirement.

When a heater is serviced or rebuilt, these items listed below need to be addressed to insure proper operation.

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(1) Heater core;The heart of the system deteriorates, causing leakage, or at the least impedes water flow, thereby reducing efficiency.

(2) Seals; Used to prevent air leakage past heater core and flapper doors. Made of a foam rubber material. Very seldom are more than just remnants that resemble dust remain.

(3) Defroster plenum; Made of a pressed paper, when exposed to moisture and heat, transforms this part into a crispy, warped unusable piece. Durable new replacement units are constructed of a superior quality plastic material and feature enhanced airflow characteristics.

(4) Heater control cables; 65-66 cables are of an all metal construction with a rubberized coating, all 3 cables are still available as the ends tend to break. Starting in 1967 cables were constructed from a wire-reinforced plastic shrouded material. These cables are joined together and often break at the mounting bracket area and are reproduced as a set of all three.

(5) Defroster hoses and "cones"; Designed to transfer heated air to the windshield area. Pressed paper cones and the thin cloth type ducting on early cars are usually worn and torn causing air to escape under the dash area.

(6) Heater hoses; Should be replaced after a few years of service. Cars without air conditioning use about 6 feet of 5/8 hose. Opt for high quality hose whenever possible. Check the condition of all hose clamps and replace with the proper size if necessary.

(7) 1 gallon of fresh antifreeze/coolant, 13# radiator cap.

(8) Condition of electrical circuit; switch, motor, resistor, fuses etc..


5/16, 3/8 and7/16'' socket/ratchet and short extension. (wrenches can be used)

Standard screwdriver if needed for hose clamps, and to remove snap clips holding case halves together.

High quality spray adhesive to replace seals.

Your trusty oil can.


Heater removal;

Drain coolant from radiator by screwing in the petcock valve. Remove both heater hoses at the engine.

Remove the four nuts protruding from the firewall near the heater motor. Carefully unplug the wires that lead to the heater motor. Stubborn plugs that become stuck with age can be coaxed with a little heat from a pocket lighter.

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Inside the car, remove the wires (if so equiped) that plug into the red phenolic resin resistor plate, and move them aside.

Don't forget to remove the screw behind the glovebox that fastens the support brace at the upper cowl area!

Remove the three heater control cable retaining/adjustment screws from their respective locations at the heater box and defroster plenumn. Cables that have never been removed will have a retainer clip that must be destroyed during removal. This retainer clip is of little consequence, but replacements are available.

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Consoles and/or under dash a/c units may need to be moved or removed to provide access for heater removal.

To remove heater, reach under the dash and gently pull the heater case down and back away from the firewall. Be sure not to let the heater hoses snag on any under hood obstacles! Coolant will not drain from hoses if they are kept above the heater cores level, or they could be plugged off. Sometimes heater hoses have been spliced or have had a coolant flush adapter installed. if so, cut or remove to allow hoses to pass through the firewall. duh.

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Once the heater is out of the vehicle, separate the case by removing clips with a screwdriver exactly as shown above. Other methods of removal are prone to breaking the brittle fiberglass housing!!

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Inspect the case for cracks or warpage. Sometimes flapper doors can be trimmed or filed to provide clearance. Broken fiberglass can usually be repaired, but it takes a bit of an artist to make it look good.

Don't force open the vent door if the hinges have rusted closed. Like the Tin Man from Oz, a little oil and gentle pressure at the hinge with a pair of pliers, slowly working the hinge pivots, movement can generally be achieved. Carelessness can destroy the heater vent door!

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Check heater motor operation with a well charged 12v battery or healthy charger. Oil armature shaft behind the squirrel cage fan. Do not remove the fan unless it is unavoidable as it is commonly rusted to the armature shaft. Pulling on the fan can distort it's frame, throwing the unit out of balance.

Study the instructions and exploded view, as depicted in the diagram included with your new seal kit, clean old foam remnants from flapper doors and around core, use a quality adhesive (3m spray or contact cement) to replace the foam .

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