A/C Signal: Description and Operation

A/C CLUTCH CONTROL RELAY
The A/C clutch control relay is used by the PCM to turn On or Off the A/C compressor clutch coil. When the PCM receives an A/C request signal, it will supply a ground to the A/C clutch control relay, energizing the relay and allowing the A/C compressor clutch coil to be energized. This allows the A/C compressor to be turned On. During certain driving conditions, the PCM will turn Off the A/C compressor by removing the ground for the A/C clutch control relay.

For more information on the air conditioning system, refer to the "HVAC Service Manual."


AIR CONDITIONER CLUTCH CONTROL
When the PCM receives an A/C request signal it will supply a ground to the A/C control relay allowing the A/C compressor to operate. During the following conditions the PCM will turn Off, or shut down A/C operation.

1. If the coolant temperature exceeds 118°C (244°F). A/C will be turned On again when coolant temperature decreases to 113°C (234°F).
2. During periods of wide-open throttle acceleration for up to 15 seconds. (Wide-open throttle is defined as throttle position sensor greater than 95% vehicle with an automatic transaxle, and 90% on vehicles with a manual transaxle.)
3. If vehicle speed is less than 16 km/h (10 mph), manifold air temperature is greater than 45°C (113°F) and throttle position sensor shows an increase greater than 8%. A/C will be shut-off for 0.3 seconds with an automatic transaxle or 1.3 seconds for a manual transaxle.
4. If engine rpm exceeds 6500 rpm. A/C will be turned back On when rpm is less than 4500 rpm for two seconds.
5. If A/C high side exceeds 2758±138 kPa (400±20 psi). A/C will be turned On when A/C high side pressure drops below 1724±3450 kPa (250±50 psi).
6. If ambient temperature, measured at the air temperature sensor, is between 4°C and 20°C (40°F and 60°F) and vehicle speed is greater than zero, the PCM will cycle the A/C compressor once every 90 seconds depending on manifold air temperature and vehicle speed.

IMPORTANT: The compressor contains a high pressure switch that can turn the clutch Off and the PCM will think the compressor is still On. This will affect the IAC learning process.

A/C REQUEST
The A/C request input is received from the A/C control head. When the A/C is turned On, a B+ signal from the A/C switch, located in the A/C control head, is sent to the PCM. If the A/C low-and high-pressure switches are closed then the B+ signal is received by the PCM. This signal notifies the PCM that the operator of the vehicle has requested that the A/C system be turned On. If engine conditions allow, the PCM will energize the A/C coil relay by supplying a ground.