The A/C electrical system consists of the following components:
A/C System Components
| • | A/C Refrigerant Pressure Sensor |
| • | A/C Compressor Clutch Relay |
| • | 12 volt A/C request signal (C60, C34) |
A/C Request Signal
This signal is transmitted through a 12 volt signal from the Front(C60)
HVAC Controller to the PCM, the 12.0 volt signal indicates that an A/C mode
is selected. The PCM uses this information to adjust the idle speed before
turning on the A/C clutch. If this signal is not available to the PCM, the
A/C Compressor will be inoperative. Refer to
Powertrain Control Module Controlled Air Conditioning (A/C) Circuit Diagnosis
for A/C clutch wiring diagrams
and diagnosis of A/C clutch electrical system. When diagnosing the refrigerant
portion of the HVAC system, the
Cooling Insufficient - Air Conditioning (A/C) System
diagnosis in Heating, Ventilation and Air Conditioning
should be used.
A/C Refrigerant Pressure Sensor
The A/C refrigerant pressure
sensor signal indicates high side refrigerant pressure to the PCM. The PCM
uses this information to adjust the idle air control valve to compensate
for the higher engine loads present with high A/C refrigerant pressures
and to control the cooling fans. A fault in the A/C refrigerant pressure
sensor signal will cause
DTC P0530 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit
to set.
When A/C is selected through the HVAC controller the PCM
increases the engine idle speed just prior to A/C clutch engagement
for better idle quality. In addition the PCM will command
the cooling fans on during A/C operation. The PCM monitors
the A/C refrigerant pressure. If the A/C refrigerant pressure,
and engine operating conditions are within a specific calibrated
acceptable ranges the PCM will enable the A/C compressor
relay. This is accomplished by providing a ground path
for the A/C relay coil within the PCM. When the A/C compressor
relay is enabled battery voltage is supplied to the compressor
clutch coil.
The PCM will enable the A/C compressor clutch whenever the engine is
running and the A/C has been requested from the front A/C Control Assembly,
unless any of the following conditions are met:
| • | Throttle more than 90 percent |
| • | A/C head pressure more than 427 psi (4.27 volts)
or less than 41 psi (0.35 volt) (as determined by the A/C refrigerant
pressure sensor). |
| • | Ignition voltage below 9.5 volts. |
| • | Engine speed more than 6900 RPM for 5 seconds. |
| • | ECT more than 121°C (250°F). |
| • | IAT less than 0°C (32°F) |
For more information regarding the A/C System, refer to
HVAC Compressor Controls Circuit Description
in HVAC Systems -
Manual.
