P1110 — A/C control interrupted | A/C signal disconnected

Causes

• Open or shorted wiring in the A/C request/control circuit
• Faulty A/C request switch or A/C control module (HVAC head unit)
• Defective A/C compressor clutch or clutch coil circuit (relay, fuse, connector)
• Faulty A/C pressure/temperature switch or sensor that interrupts the request
• Poor or corroded ground or battery/ignition supply to the A/C control circuit
• Intermittent or failed ECM input for the A/C request signal

Symptoms

• A/C not engaging or compressor clutch not activating
• No response when A/C switch is turned on from HVAC controls
• Intermittent A/C operation
• Possible dashboard A/C indicator or warning lamp
• Related drivability issues if the ECM reduces load or changes idle strategy

What to check

• Read stored and pending trouble codes and freeze-frame data with a factory-level or OBD-II scan tool.
• Verify ignition on and check presence of related fuses and A/C relays; inspect for blown fuse.
• Visually inspect wiring, connectors and grounds for the HVAC unit, A/C clutch and ECM.
• Check for corrosion, bent pins or water ingress at connectors (HVAC head, compressor, pressure switch, ECM).
• Measure voltage at A/C request/control pin with HVAC switch ON (expected battery voltage or logic signal depending on model).
• Check continuity between HVAC module A/C request output and ECM input; check continuity to compressor clutch/relay.

Signal parameters

• A/C request output: typically switched battery voltage (approx. 12 V) when ON or low-logic ground depending on vehicle wiring
• A/C request input to ECM: logic level expected (0 V when inactive or ~12 V when active) — verify against factory pinout
• Compressor clutch coil resistance: typically a few ohms (varies by model) — compare to specification
• Relay control: coil should see battery voltage and ground when energized; control side should show continuity
• CAN bus idle voltages (if applicable): approx. 2.5 V on CAN High/Low differential levels when intact

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