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HOMESERVICE MANUALSMERCURY2008MARINER 2WD V6-3.0LREPAIR AND DIAGNOSISHEATING AND AIR CONDITIONINGSENSORS AND SWITCHES - HVACREFRIGERANT PRESSURE SENSOR / SWITCHDESCRIPTION AND OPERATIONDUAL-FUNCTION PRESSURE SWITCH
2008 Mercury Mariner 2WD V6-3.0L
Dual-Function Pressure Switch
2008 Mercury Mariner 2WD V6-3.0LSECTION Dual-Function Pressure Switch
Dual-Function Pressure Switch
The dual-function pressure switch is located on the receiver drier and includes 2 separate sets of contacts that are opened at 2 different pressures.
The first set of contacts in the dual-function pressure switch is used to interrupt A/C compressor operation in the event of excessively high discharge pressure in the high-pressure side of the refrigerant system. The PCM monitors the first set of contacts in the dual-function pressure switch in-series with the low-charge protection switch. When the contacts are open, the PCM will disengage the A/C compressor clutch.
The second set of contacts in the dual-function pressure switch is used by the PCM to engage the high-speed cooling fan. The PCM monitors the second set of contacts through the A/C pressure (ACP) circuit. When the A/C pressure rises above a preset level, the second set of contacts will close and the high-speed cooling fan will be engaged.
The dual-function pressure switch is installed on a Schrader-type valve core fitting on the receiver/drier. It is not necessary to recover the refrigerant to remove the dual-function pressure switch.
Low-Charge Protection Switch
The low-charge protection switch is installed on the evaporator outlet line to cycle the A/C compressor off in the event of a low refrigerant charge. The PCM monitors the low-charge protection switch in-series with the dual-function pressure switch. When the low-side pressure drops below acceptable levels, the low-charge protection switch contacts open. When the low-charge protection switch contacts are open, the PCM will disengage the A/C compressor clutch.
The low-charge protection switch is installed on a Schrader-type valve core fitting on the evaporator outlet line. It is not necessary to recover the refrigerant to remove the low-charge protection switch.
The dual-function pressure switch is located on the receiver drier and includes 2 separate sets of contacts that are opened at 2 different pressures.
The first set of contacts in the dual-function pressure switch is used to interrupt A/C compressor operation in the event of excessively high discharge pressure in the high-pressure side of the refrigerant system. The PCM monitors the first set of contacts in the dual-function pressure switch in-series with the low-charge protection switch. When the contacts are open, the PCM will disengage the A/C compressor clutch.
The second set of contacts in the dual-function pressure switch is used by the PCM to engage the high-speed cooling fan. The PCM monitors the second set of contacts through the A/C pressure (ACP) circuit. When the A/C pressure rises above a preset level, the second set of contacts will close and the high-speed cooling fan will be engaged.
The dual-function pressure switch is installed on a Schrader-type valve core fitting on the receiver/drier. It is not necessary to recover the refrigerant to remove the dual-function pressure switch.
Low-Charge Protection Switch
The low-charge protection switch is installed on the evaporator outlet line to cycle the A/C compressor off in the event of a low refrigerant charge. The PCM monitors the low-charge protection switch in-series with the dual-function pressure switch. When the low-side pressure drops below acceptable levels, the low-charge protection switch contacts open. When the low-charge protection switch contacts are open, the PCM will disengage the A/C compressor clutch.
The low-charge protection switch is installed on a Schrader-type valve core fitting on the evaporator outlet line. It is not necessary to recover the refrigerant to remove the low-charge protection switch.
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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.