A/C Request Signal

ECM Controlled A/C
The Air Conditioning (A/C) request circuit signals the ECM when you select an A/C mode at the A/C control head. The ECM uses this information in order to enable the A/C compressor clutch and in order to adjust the idle speed before turning ON the A/C clutch. If this signal is not available to the ECM, the A/C compressor will be inoperative.

A/C Clutch Circuit Description
The A/C compressor operation is controlled by the ECM in order to improve the engine operation and to protect the A/C compressor and the A/C clutch during a Wide Open Throttle (WOT) performance.


Operation
This A/C system consists of the following components:

^ The heater and A/C control
^ The A/C load signal switch
^ The A/C refrigerant pressure switch (low and high)
^ The A/C clutch relay
^ The A/C compressor clutch
^ The ECM.

The A/C refrigerant pressure cycling switch is closed when there is sufficient system pressure (depending on the refrigerant charge and the ambient temperature). When the heater and the A/C control is placed in the A/C mode, a request signal is sent to the ECM. The ECM will then energize the A/C clutch relay, unless an abnormally high or low A/C pressure is detected by the A/C refrigerant pressure sensor. The cooling fans are controlled by temperature switches and are not controlled by the ECM. Refer to Cooling System for more information on the cooling fan operation. The A/C clutch relay is controlled by the ECM so that the ECM can increase the idle speed before turning on the clutch or disable the clutch during WOT, or high coolant temperature. The A/C load switch will also signal the ECM to increase the idle speed by approximately 50 RPM in order to compensate for heavy load on the A/C system due to, for example, high ambient conditions.