Coolant Temperature Override (CTO) Switch
- Ensure coolant temperature is below 160°F. Remove all vacuum hoses from CTO switch. Plug hoses that cause vacuum leak. Connect a vacuum hose from a manifold vacuum source to carburetor port of CTO. Connect vacuum gauge to manifold port of CTO. See Fig 1.
- Start engine. Manifold vacuum should be present on vacuum gauge. If not, replace CTO switch. With engine still running and coolant temperature above 160°F, vacuum should NOT be present at gauge. If vacuum is present, replace CTO switch.
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