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 MANUALSCHEVROLET2008CHEVY EXPRESS G3500, VAN PASSENGER EXTENDEDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 21 (HVAC SYSTEM - MANUAL)DIAGNOSTIC INFORMATION AND PROCEDURESSCAN TOOL OUTPUT CONTROLS
2008 Chevrolet Chevy Express G3500, Van Passenger Extended
Scan Tool Output Controls
2008 Chevrolet Chevy Express G3500, Van Passenger ExtendedSECTION Scan Tool Output Controls
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HVAC Control Module Scan Tool Output Controls
| Scan Tool Output Control | Additional Menu Selection(s) | Description |
|---|---|---|
| A/C Permission | Miscellaneous Tests | When you select ON, the HVAC control module changes the state of the A/C Permission parameter to Granted and transmits a clutch enable message to the PCM over the class 2 serial data circuit. The A/C compressor clutch engages and remains engaged until you select OFF. When you select OFF, the HVAC control module changes the state of the A/C Permission parameter to Withheld and transmits a clutch disable message to the PCM over the class 2 serial data circuit. |
| Left Mix Motor | Motor/Actuator Tests | When you select ON, the HVAC control module commands the left air temperature actuator toward the maximum door position. The actuator moves the door to the full hot position. When you select OFF, the HVAC control module commands the left air temperature actuator toward the minimum door position. The actuator moves the door to the full cold position. |
| Mode 1 Door Position | Motor/Actuator Tests | When you select ON, the HVAC control module commands the mode actuator toward the maximum door position. The actuator moves the door to the panel position. When you select OFF, the HVAC control module commands the mode actuator toward the minimum door position. The actuator moves the door to the floor position. |
| Right Mix Motor | Motor/Actuator Tests | When you select ON, the HVAC control module commands the right air temperature actuator toward the maximum door position. The actuator moves the door to the full cold position. When you select OFF, the HVAC control module commands the right air temperature actuator toward the minimum door position. The actuator moves the door to the full hot position. |
PCM Scan Tool Output Controls
| Scan Tool Output Control | Additional Menu Selection(s) | Description |
|---|---|---|
| A/C Relay | Engine Output Controls | The engine must be running and the PCM must receive an A/C request from the HVAC control module in order to enable the output control. The PCM de-energizes the A/C compressor clutch relay when you select OFF. The relay remains de-energized until you select ON. |
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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.