Replace the heater control valve on a 1966 Chevrolet Corvette 327ci V8 to restore proper heating system temperature control.

Warnings

Tools required

Parts

• Heater control valve × 1 — Use OEM specification
• Heater hose clamps (5/8 inch) × 2 — Use OEM specification
• Coolant (if needed for top-off) × 1 — DEX-COOL Extended Life

Fluids

• DEX-COOL Extended Life (Orange) — 1 qt

Preparation

1. Ensure engine is completely cold to the touch
2. Place drain pan under radiator and open radiator petcock to drain coolant to a level below the heater control valve (approximately 2-3 quarts)
3. Locate the heater control valve on the passenger side firewall area where the heater hose connects
4. Note the orientation and cable attachment position of the existing valve for proper installation
5. Have shop rags ready to catch residual coolant from hoses

Procedure

1. 1

   Access heater control valve
   From the engine compartment, locate the heater control valve mounted on the firewall passenger side. The valve will have two heater hoses connected and a control cable or vacuum line attached. Clear any obstructions such as ignition wires or hoses that may interfere with access.
2. 2

   Disconnect control cable
   Disconnect the heater control cable from the lever arm on the heater control valve. On 1966 Corvettes, this is typically a mechanical cable with a clip or set screw attachment. Use a flathead screwdriver to release the cable retaining clip, then slide the cable end off the valve lever arm. Note the exact position and routing for reinstallation.
3. 3

   Position drain pan
   Place the drain pan directly beneath the heater control valve area. Position shop rags around the valve and hose connections to catch coolant spillage. Even with the radiator partially drained, residual coolant will remain in the heater hoses and block.
4. 4

   Remove inlet hose clamp
   Locate the inlet hose clamp (coming from the engine block or intake manifold). This is typically the lower connection on the valve. Use pliers or hose clamp pliers to squeeze and slide the clamp back along the hose at least 2 inches away from the valve connection. If the clamp is a worm-gear style, loosen it with a flathead screwdriver instead.
   ⚠Coolant will begin draining immediately when the hose is removed. Have rags ready.
5. 5

   Remove inlet hose
   Twist the inlet hose back and forth while pulling to break the seal and remove it from the heater control valve inlet port. If the hose is stuck due to age, carefully use a razor blade to cut lengthwise along the hose end at the connection point, taking care not to damage the valve port. Allow coolant to drain into the pan.
6. 6

   Remove outlet hose clamp
   Locate the outlet hose clamp (going to the heater core). This is typically the upper connection on the valve. Use pliers to squeeze and slide the clamp back along the hose at least 2 inches away from the valve connection, or loosen with a flathead screwdriver if worm-gear style.
7. 7

   Remove outlet hose
   Twist the outlet hose back and forth while pulling to remove it from the heater control valve outlet port. Use the same razor blade technique if the hose is stuck. Allow remaining coolant to drain.
8. 8

   Remove old valve mounting
   The heater control valve is typically held by a mounting bracket attached to the firewall with a single bolt or clip. Remove this fastener and detach the old valve from the vehicle. Note the bracket orientation for reinstallation.
9. 9

   Prepare new valve
   Inspect the new heater control valve to confirm it matches the original configuration (inlet/outlet port sizes, mounting bracket position, control lever orientation). If the new valve includes a mounting bracket, transfer it to match the original orientation. Ensure the valve lever moves freely through its full range of motion.
10. 10

    Install new valve
    Position the new heater control valve in the mounting bracket location on the firewall, ensuring the inlet and outlet ports align with their respective hoses. Secure the mounting bracket with the original fastener. Confirm the control lever is accessible and positioned correctly for cable reattachment.
11. 11

    Install hoses
    Connect the inlet hose to the valve inlet port first, pushing it fully onto the port until it seats completely. Slide the clamp into position 1/2 inch from the end of the hose and tighten securely. Repeat for the outlet hose to the valve outlet port. Ensure both hoses are fully seated with no gaps visible at the connections.
12. 12

    Reconnect control cable
    Reattach the heater control cable to the valve lever arm in the exact position noted during disassembly. Secure the cable end with the retaining clip. Test the cable operation by moving the heater control inside the vehicle from cold to hot and back, verifying the valve lever moves through its full range without binding.
13. 13

    Refill cooling system
    Close the radiator petcock. Refill the cooling system with conventional green ethylene glycol (IAT) coolant mixed 50/50 with distilled water through the radiator cap opening. Fill until coolant reaches the base of the filler neck. Start the engine with the radiator cap off and allow it to warm to operating temperature, adding coolant as the level drops during system burping.
14. 14

    Bleed air and check for leaks
    With the engine at operating temperature, carefully add coolant to bring the level to proper specification. Install the radiator cap. Inspect all heater control valve connections for coolant leaks. Check under the valve and along the hoses for any drips or seepage. Test the heater operation by setting the control to hot and verifying warm air flows from the vents.

Reassembly

1. Double-check all hose clamps are tight and properly positioned
2. Verify control cable operates smoothly without binding through full range
3. Confirm coolant level is correct after system has fully burped

Verification

• Start engine and allow to reach normal operating temperature with no overheating
• Verify no coolant leaks at heater control valve connections or mounting area
• Test heater operation by moving control from cold to hot position and confirming immediate temperature change in cabin air
• Check coolant level when cold after test drive and top off if necessary
• Verify valve lever moves freely when heater control is operated from inside vehicle

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