Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Temperature Control Lever Operation
When the temperature control lever is placed at COOL, the plunger on the water valve vacuum switch depressed, connecting the water valve vacuum motor to vacuum which causes the valve to close and shut off water flow to the heater core. Also at COOL position, the lever has caused the temperature door to be positioned to by-pass all directly to the plenum chamber unheated. Moving the lever away from COOL approximately 1/4" causes the vacuum switch to disconnect the water valve motor from vacuum. The valve then opens to allow hot water to flow through the heater core.
As the temperature control lever is moved further from COOL to WARM, the control cable moves the temperature blend door from minimum heat to full heat position to modulate the air flow through and/or around the heater core. The air through the core is then mixed with air from the by-pass chambers as it enters the plenum chamber. At full WARM position of the lever, the by-pass is shut off, and all the air passes through the heater core before entering the plenum chamber.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.