this is off gm's service site, if you need any more info or a scanner let me know I have a tech2
A/C Low Pressure Switch
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). 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). 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.
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Don
Traveling Man