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.
All Mode Selector Valve Positions Leak
1986 Mercury Sable LS, 4D SedanSECTION All Mode Selector Valve Positions Leak
- Move temperature control lever from 65° to 85°. If hiss stops at some settings, go to next test. If hiss continues, check Black vacuum source tube from reservoir to control assembly for cuts or disconnection and repair if necessary.
- If no problem is found, pinch off source tube at control assembly. If hiss stops, replace selector valve.
- If hiss continues, pinch off source tube at diverter valve. If hiss stops, replace servo assembly. If hiss continues, pinch off source tube at TBL switch.
- If hiss stops, replace TBL switch. If hiss continues, pinch off source tube at ATC sensor.
- If hiss stops, go to step 6). If hiss continues, recheck source tube connections, reservoir and check valve.
- Pinch off Tan tube at ATC sensor. If hiss stops, go to step 7). If hiss continues, replace ATC sensor.
- Pinch off Tan tube at servo motor. If hiss stops, replace servo motor. If hiss continues, repair tube.
RENDER: 1.0x
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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.