The A/C electrical system consists of the following components:
A/C System Components
| • | A/C Refrigerant Pressure Sensor |
| • | A/C Compressor Clutch Relay |
| • | Class II Serial Data Circuit (CJ2) |
| • | 12 volt A/C request signal (CJ3, C60) |
A/C Request Signal
This signal is transmitted two different ways depending on the content
option, the first is communicated Class II from the HVAC Controller
to the PCM that an A/C mode is selected (CJ2). The second is a 12 volt signal
from the HVAC Controller to the PCM, the 12.0 volt signal indicates that an
A/C mode is selected (CJ3, C60). 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 HVAC 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, 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
Air Conditioning (A/C) System Description
in Heating, Ventilation and Air Conditioning,
HVAC Compressor Controls Circuit Description
in
HVAC Systems - Manual, and
HVAC Compressor Controls Circuit Description
in HVAC Systems - Automatic.
