Manual:HUMMER Hummer H3 Base 2010Page:14924 / 37523



Heating and A/C Operation — 2010 Hummer H3 Base, Automatic Service Manual

Heating and A/C Operation

The purpose of the heating and A/C system is to provide heated and cooled air to the interior of the vehicle. The A/C system will also remove humidity from the interior and reduce windshield fogging. The vehicle operator can determine the passenger compartment temperature by adjusting the air temperature switch. Regardless of the temperature setting, the following can effect the rate that the HVAC system can achieve the desired temperature:

  • Recirculation
  • Difference between inside and desired temperature
  • Difference between ambient and desired temperature
  • Blower motor speed setting
  • Mode setting

The vehicle operator can activate the A/C system by pressing the A/C switch. The A/C system can operate regardless of the air temperature or mode setting. When the A/C switch is pressed, the HVAC control assembly applies 10 volts to the A/C request signal circuit. The voltage is then sent through the evaporator temperature sensor, if the evaporator temperature is above 0°C (32°F), then the voltage is applied to the other A/C request signal circuit to the BCM. The BCM receives the voltage input and sends a class 2 message to the PCM for an A/C request.

The PCM will operate the A/C system automatically in FRONT DEFROST mode to help reduce moisture inside the vehicle. The A/C LED will not illuminate unless the driver presses the A/C request switch on the HVAC control assembly. The A/C system maybe running without the A/C LED indicator illuminated when in FRONT DEFROST mode or Recirc. The following conditions must be met in order for the PCM to turn on the compressor clutch:

  • BCM
    • Battery voltage is between 9-16 volts.
    • A/C request from the HVAC control assembly
  • PCM
    • Engine coolant temperature (ECT) is less than 123°C (253°F).
    • Engine speed is less than 5300 RPM.
    • Engine speed is more than 600 RPM.
    • A/C high side pressure is between 2951-310 kPa (428-44 psi).

Once engaged, the compressor clutch will be disengaged for the following conditions:

  • Throttle position is 100 percent for 10 seconds.
  • A/C high side pressure is more than 2951 kPa (428 psi) and will re-engage once the pressure drops below 2068 kPa (300 psi).
  • A/C high side pressure is less than 310 kPa (44 psi).
  • Evaporator temperature is less than 0°C (32°F)
  • Engine coolant temperature (ECT) is more than 123°C (253°F).
  • Engine speed is less than 475 RPM.
  • Engine speed is more than 6000 RPM.
  • PCM detects excessive torque load.
  • PCM detects insufficient idle quality.
  • If the blower is switched to off.

When the compressor clutch disengages, the compressor clutch diode protects the electrical system from a voltage spike.