Sparky2263
08-20-05, 11:00 PM
The A/C system can operate regardless of the temperature setting, as long as the ambient air temperature is above 3°C (37°F) degrees . If the A/C compressor clutch is turned off due to cold ambient air temperatures, the compressor will not come back on until ambient air temperatures reach 5°C (41°F) .
Regardless of the selected A/C mode setting, a request is made to the Powertrain Control Module (PCM) to turn on the A/C compressor. The request is made through the A/C request signal circuit from the HVAC control assembly. Power and ground are provided to the HVAC control assembly by the ignition 3 voltage, ground circuits and splice pack.
In order for the PCM to internally ground the A/C clutch relay control circuit, two separate request signals need to be grounded. A 12-volt request signal is sent out over the A/C request signal circuit, through the A/C high pressure switch, and grounded through the PCM when the vehicle operator makes an A/C request. A separate 12-volt request signal is sent out over the A/C low pressure switch signal circuit, through the A/C low pressure switch and the ground circuit. When both these request signals is grounded, the PCM can activate the A/C compressor clutch.
The PCM turns on the A/C compressor by providing a path to ground through the A/C clutch relay control circuit for the A/C compressor clutch relay. Power is provided to the A/C compressor clutch relay internally of the underhood fuse block. Once the relay closes its internal switch, power from the battery is provided to the A/C compressor clutch through the A/C compressor clutch supply voltage circuit. Whenever the compressor is turned off, the A/C compressor clutch diode prevents a voltage spike from burning up the Compressor clutch coil.
The ground circuit and underhood fuse block provides a path to ground for the compressor. The A/C clutch relay control circuit is grounded internally within the PCM.
The A/C system is protected by two pressure switches. The A/C high pressure switch interrupts the A/C request signal when the A/C line pressures climb above 2826 kPa (410 psi) . The A/C low pressure switch interrupts the A/C low pressure switch signal when the A/C line pressure fall below 207 kPa (30 psi) . When the PCM sees an open in either signal, the A/C clutch relay control circuit is no longer grounded, thus shutting off the compressor. When high side pressures drop back down between 1034-1724 kPa (150-250 psi) , the PCM will allow the A/C compressor to operate.
(Courtesy General Motors)
Regardless of the selected A/C mode setting, a request is made to the Powertrain Control Module (PCM) to turn on the A/C compressor. The request is made through the A/C request signal circuit from the HVAC control assembly. Power and ground are provided to the HVAC control assembly by the ignition 3 voltage, ground circuits and splice pack.
In order for the PCM to internally ground the A/C clutch relay control circuit, two separate request signals need to be grounded. A 12-volt request signal is sent out over the A/C request signal circuit, through the A/C high pressure switch, and grounded through the PCM when the vehicle operator makes an A/C request. A separate 12-volt request signal is sent out over the A/C low pressure switch signal circuit, through the A/C low pressure switch and the ground circuit. When both these request signals is grounded, the PCM can activate the A/C compressor clutch.
The PCM turns on the A/C compressor by providing a path to ground through the A/C clutch relay control circuit for the A/C compressor clutch relay. Power is provided to the A/C compressor clutch relay internally of the underhood fuse block. Once the relay closes its internal switch, power from the battery is provided to the A/C compressor clutch through the A/C compressor clutch supply voltage circuit. Whenever the compressor is turned off, the A/C compressor clutch diode prevents a voltage spike from burning up the Compressor clutch coil.
The ground circuit and underhood fuse block provides a path to ground for the compressor. The A/C clutch relay control circuit is grounded internally within the PCM.
The A/C system is protected by two pressure switches. The A/C high pressure switch interrupts the A/C request signal when the A/C line pressures climb above 2826 kPa (410 psi) . The A/C low pressure switch interrupts the A/C low pressure switch signal when the A/C line pressure fall below 207 kPa (30 psi) . When the PCM sees an open in either signal, the A/C clutch relay control circuit is no longer grounded, thus shutting off the compressor. When high side pressures drop back down between 1034-1724 kPa (150-250 psi) , the PCM will allow the A/C compressor to operate.
(Courtesy General Motors)