A/C Low Pressure Switch

WARNING: This page is about a different car, the 2007 Hummer H2. However, it is still accessible from the selected car via links, so may be relevant.

The A/C low pressure switch protects the A/C System from a low pressure condition that could damage the A/C compressor or cause evaporator icing. The HVAC control module applies 5 volts to the A/C low pressure switch signal circuit. The switch will open when the A/C low side pressure reaches 138-172 kPa (20-25 psi) as measured at the switch/accumulator. This prevents the A/C compressor from operating. The switch will then close when A/C low pressure side reaches 275-317 kPa (40-46 psi) as measured at the switch/accumulator. This enables the A/C compressor to turn back ON.

The low pressure switch uses refrigerant pressure to open and close a set of electrical contacts. When A/C request is authorized the switch is closed and shows normal status. During this state the switch will show 0 volts on the A/C low pressure sensor signal circuit. When A/C request is denied due to a low pressure condition the switch will be open. During this state the switch will show 5 volts on the A/C low pressure sensor signal circuit.