Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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 165-200 kPa (24-29 psi). This prevents the A/C compressor from operating. The switch will then close when A/C low pressure side reaches 275-310 kPa (40-45 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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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.