Heater Control Valve

Replacement of the heater control valve on the 1992 Dodge Viper, which regulates coolant flow to the heater core. Requires partial coolant drain and firewall access.

Warnings

Tools required

Parts

• Heater control valve × 1 — Use OEM specification
• Hose clamps (if original clamps damaged) × 2 — Worm-drive style, appropriate size for heater hoses

Fluids

• coolant — 3 qt

Preparation

1. Ensure engine is completely cold to the touch (minimum 2 hours after last operation).
2. Park vehicle on level surface and engage parking brake.
3. Place drain pan under radiator drain petcock.
4. Open hood and secure in fully open position.

Procedure

1. 1

   Drain Coolant (Partial)
   Open the radiator drain petcock at the bottom of the radiator and drain approximately 2-3 gallons of coolant into the drain pan. This lowers the coolant level below the heater control valve to minimize spillage. Once coolant level drops below the upper radiator hose connection, close the petcock hand-tight.
   Torque spec

   Drain Petcock7 Nm (5 lb-ft)
2. 2

   Locate Heater Control Valve
   The heater control valve is located on the passenger side firewall, inline with the heater hose that runs from the engine to the heater core. It is a cylindrical valve body with a vacuum actuator attached. Trace the heater hoses from the engine bay to identify the valve position.
   ℹ️On the 1992 Viper, the valve is positioned between the engine and firewall near the passenger side cylinder bank. Access is tight but workable from above.
3. 3

   Disconnect Vacuum Line
   Locate the vacuum line connected to the actuator port on top of the heater control valve. Carefully pull the vacuum line straight off the nipple. Note the routing of this vacuum line for reinstallation—it typically runs to the HVAC control head inside the cabin via a firewall grommet. Have shop towels ready as residual coolant may drip from the valve.
   ⚠Vacuum lines on this vehicle may be brittle. If the line breaks during removal, replacement vacuum line will be required.
4. 4

   Remove Inlet Hose Clamp
   Identify the inlet heater hose (coming from the engine). Using hose clamp pliers or a screwdriver, loosen or remove the hose clamp securing the inlet hose to the heater control valve. Slide the clamp back along the hose away from the valve connection point.
   ℹ️Factory clamps may be spring-type or worm-drive. Inspect clamp condition and replace if corroded or damaged.
5. 5

   Remove Outlet Hose Clamp
   Identify the outlet heater hose (going to the heater core through the firewall). Using hose clamp pliers or a screwdriver, loosen or remove the hose clamp securing the outlet hose to the heater control valve. Slide the clamp back along the hose away from the valve connection point.
6. 6

   Disconnect Heater Hoses
   Twist each heater hose gently while pulling to break the seal, then pull both hoses off the heater control valve nipples. Position the hose ends upward or plug them temporarily to minimize coolant spillage. Have shop towels and a catch container ready for coolant that will drain from both the valve and hoses. Expect approximately 0.5-1 quart of coolant loss during this step.
   ⚠Hoses may be adhered to the valve nipples after years of service. Do not use excessive force or pry tools that could damage the hose ends.
7. 7

   Remove Valve Mounting Hardware
   The heater control valve is secured to a mounting bracket on the firewall with 2 bolts. Remove these mounting bolts and carefully extract the valve from the engine bay. Note the orientation of the valve—the inlet and outlet ports must face the correct direction for hose routing.
   Torque spec

   Valve Mounting8 Nm (6 lb-ft)
8. 8

   Inspect Mounting Bracket and Hoses
   With the valve removed, inspect the mounting bracket for damage or corrosion. Inspect both heater hoses for cracks, softness, or deterioration. Check hose ends for damage that occurred during removal. Replace hoses if any degradation is present—the Viper's high operating temperatures accelerate hose aging.
   ℹ️This is an ideal time to replace aging heater hoses if they show any signs of wear, as access is already achieved.
9. 9

   Install New Heater Control Valve
   Position the new heater control valve in the mounting bracket with the inlet port oriented toward the engine and outlet port toward the firewall. Ensure the vacuum actuator is accessible from above. Install the 2 mounting bolts and torque to specification.
   Torque spec

   Valve Mounting8 Nm (6 lb-ft)
10. 10

    Reconnect Heater Hoses
    Push the inlet heater hose firmly onto the valve inlet nipple until it seats completely. Push the outlet heater hose firmly onto the valve outlet nipple until it seats completely. Ensure both hoses are fully seated with no gaps visible between hose end and valve body.
11. 11

    Install Hose Clamps
    Position the inlet hose clamp over the hose connection point and tighten to specification. Position the outlet hose clamp over the hose connection point and tighten to specification. Ensure clamps are positioned approximately 1/4 inch from the end of each hose, centered over the nipple bead.
    Torque spec

    Hose Clamps3 Nm (2 lb-ft)
12. 12

    Reconnect Vacuum Line
    Push the vacuum line firmly onto the actuator nipple on top of the heater control valve until it seats completely. Verify the vacuum line routing matches the original path noted during removal, with no kinks or tight bends that could restrict vacuum signal.
13. 13

    Refill Coolant System
    Using a funnel, add ethylene glycol 50/50 coolant mixture to the radiator until the level reaches the bottom of the filler neck. Add coolant slowly to allow air to escape. Start the engine and allow it to warm to operating temperature with the radiator cap off. Add additional coolant as the level drops during thermostat opening and air purging. Once the engine reaches operating temperature and coolant level stabilizes, install the radiator cap. Note: Refill the amount of coolant that was drained in Step 1. After a partial drain of 2-3 gallons, expect to add a similar volume to restore proper level; verify exact system capacity against Viper service documentation.
    ⚠The Viper cooling system holds 24 quarts total. After partial drain, approximately 2-3 quarts will be needed to restore proper level.
    ℹ️Run heater at full hot during warm-up to purge air from heater core and verify heater control valve operation.
14. 14

    Bleed Air from System
    With the engine at operating temperature, increase RPM to 2000-2500 for 30 seconds, then return to idle. Repeat this process 3-4 times to help purge remaining air pockets. Monitor coolant level in radiator and add as needed. Check for leaks at the heater control valve connections, hose clamps, and radiator petcock. Once no air bubbles are visible in the radiator and coolant level is stable, shut off engine and install radiator cap securely.

Reassembly

1. Reassembly is covered in the installation steps above.
2. Ensure all hose clamps are tightened to specification to prevent coolant leaks.
3. Verify vacuum line is properly seated on the valve actuator nipple.
4. Double-check coolant level after initial test drive and top off if necessary.

Verification

• Start engine and verify no coolant leaks at heater control valve connections.
• Test heater operation by switching cabin temperature control from cold to hot. Verify hot air is produced when heater is on and temperature is reduced when heater is off.
• Monitor coolant level after several heat cycles to ensure system is properly filled with no air pockets.
• Check engine operating temperature remains normal (approximately 195°F) with no overheating.
• After 50-100 miles of driving, recheck all hose clamp connections for any seepage and retighten if necessary.

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