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.
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HOMESERVICE MANUALSCHEVROLET1987STEP VAN P20, 7.4 W, AUTOMATIC, 400/M40REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 14 (ENGINE CONTROLS - SYSTEM/COMPONENT TESTS - GASOLINE)ENGINE SENSORS & SWITCHESENGINE CONTROLS - SYSTEM/COMPONENT TESTS - GASOLINEA/C ON SWITCH/SYSTEM TEST
1987 Chevrolet Step Van P20, 7.4 W, Automatic, 400/M40
A/C ON Switch/System Test
1987 Chevrolet Step Van P20, 7.4 W, Automatic, 400/M40SECTION A/C ON Switch/System Test
WARNING: This page does not describe the selected car, but rather 10 other vehicles, including the 1994 GMC Yukon, 1994 GMC Suburban, 1994 GMC Pickup, 1994 GMC Cab & Chassis, and 1994 GMC C3500 HD. However, it is still accessible from the selected car via links, so may be relevant.
- Turn ignition switch to RUN position. Move mode selector switch to OFF position. With A/C control assembly connected, measure voltage between mode selector switch Dark Green wire (Dark Green/White on "L", "M" and "U" Series) and ground. For wiring schematics, see mini-schematics in A/C CLUTCH under MISCELLANEOUS ECM CONTROLS.
- Battery voltage should be present. If battery voltage is present, mode selector switch is operating normally. If battery voltage is not present, check wire from selector switch to fuse for an open circuit. Also check A/C high and low pressure switches for open.
- Check voltage between mode selector Dark Green or Dark Green/White wire and ground. Voltage should not be present. If voltage is present, replace mode selector switch.
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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.