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.
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HOMESERVICE MANUALSPLYMOUTH1985CONQUEST L4-2555CC 2.6L SOHC TURBOREPAIR AND DIAGNOSISHEATING AND AIR CONDITIONINGREFRIGERANT PRESSURE SENSOR / SWITCHLOW PRESSURE SENSOR / SWITCHTESTING AND INSPECTION
1985 Plymouth Conquest L4-2555cc 2.6L SOHC Turbo
Low Pressure Sensor / Switch: Testing and Inspection
1985 Plymouth Conquest L4-2555cc 2.6L SOHC TurboSECTION Testing and Inspection
Low Pressure Switch
The low pressure switch, is wired in series with the magnetic clutch. It cuts off the electrical power supply to the clutch when refrigerant pressure drops below the control point of the switch.
Whenever the system is inactivated by the low pressure switch due to refrigerant loss, the refrigerant oil may have been lost. Therefore, to prevent damage to the compressor due to operation without sufficient lubrication, the leak must be repaired and the compressor oil level checked before final charge of the system.
The switch is a sealed, factory calibrated unit. No attempt shall be made to adjust or otherwise repair it. If it is found to be faulty it must be replaced.
To Test the Low Pressure Switch (Engine Off)
1. Jump wire leads.
2. Press the A/C switch and blower switch on.
3. Momentarily turn the ignition switch on (do not crank the engine), listen for the clutch engaging.
4. If the clutch does not engage, the air flow thermostat, coolant temperature switch, high pressure switch or fuse may be faulty.
5. If clutch engages, connect the manifold gauge set and read pressure. At pressure of 206 kPa (30 psi) or above, switch must actuate the clutch.
If the pressure is below 206 kPa (30 psi), refrigerant system is low in charge. For corrective action refer to refrigerant leak repair procedure.
6. Reconnect wire on switch and perform step number 3. If the clutch does not engage, discharge the system, replace the switch, and recharge the system.
The low pressure switch, is wired in series with the magnetic clutch. It cuts off the electrical power supply to the clutch when refrigerant pressure drops below the control point of the switch.
Whenever the system is inactivated by the low pressure switch due to refrigerant loss, the refrigerant oil may have been lost. Therefore, to prevent damage to the compressor due to operation without sufficient lubrication, the leak must be repaired and the compressor oil level checked before final charge of the system.
The switch is a sealed, factory calibrated unit. No attempt shall be made to adjust or otherwise repair it. If it is found to be faulty it must be replaced.
To Test the Low Pressure Switch (Engine Off)
1. Jump wire leads.
2. Press the A/C switch and blower switch on.
3. Momentarily turn the ignition switch on (do not crank the engine), listen for the clutch engaging.
4. If the clutch does not engage, the air flow thermostat, coolant temperature switch, high pressure switch or fuse may be faulty.
5. If clutch engages, connect the manifold gauge set and read pressure. At pressure of 206 kPa (30 psi) or above, switch must actuate the clutch.
If the pressure is below 206 kPa (30 psi), refrigerant system is low in charge. For corrective action refer to refrigerant leak repair procedure.
6. Reconnect wire on switch and perform step number 3. If the clutch does not engage, discharge the system, replace the switch, and recharge the system.
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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.