hvac
AC Low Pressure Switch
for 1970 AMC Rebel Machine 390ci V8 · RWD
Editorial review:Chris Hackleman — Master Technician · 20+ years · Jeff Moore — Master Mechanic · 20+ years
Difficulty
Easy
Time
1.0 h
Tools
7
Steps
11
✓Expert-verified. Personally reviewed and approved by OLP's master technicians (Chris Hackleman & Jeff Moore — 20+ years each). Always follow the vehicle's factory service information and torque specs.
Replace the AC low pressure switch on a 1970 AMC Rebel Machine to restore proper air conditioning system operation and prevent compressor damage from low refrigerant conditions.
Warnings
⚠️The AC system must be properly evacuated by a certified technician with recovery equipment. Venting refrigerant to atmosphere is illegal and environmentally harmful.
⚠️Never open AC system fittings while the system is pressurized. Refrigerant can cause frostbite and eye injury.
⚠Original R-12 refrigerant is no longer available. If system has been converted to R-134a or another refrigerant, verify compatibility before recharging.
ℹ️The low pressure switch on AMC systems is typically located on the accumulator or suction line near the firewall.
Tools required
Refrigerant recovery machineEssential
Adjustable wrench or 1 inch wrenchEssential
Safety glassesEssential
Vacuum pumpEssential
AC manifold gauge setEssential
Refrigerant charging stationEssential
As an Amazon Associate and Autel/ANCEL partner, OLP earns from qualifying purchases — how we link. This never changes the specs we publish.
Parts
- AC low pressure switch × 1 — Use OEM specification for AMC A/C system
- O-ring seal for pressure switch port × 1 — Use OEM specification
As an Amazon Associate and Autel/ANCEL partner, OLP earns from qualifying purchases — how we link. This never changes the specs we publish.
Fluids
- R-12 refrigerant (or approved substitute if system converted)
Preparation
- Ensure engine is completely cool before beginning work
- Park vehicle on level surface and engage parking brake
- Open hood and locate the AC low pressure switch on the accumulator or suction line on passenger side of engine bay
- Verify the system uses R-12 or has been converted to appropriate substitute refrigerant
- Ensure proper EPA-approved refrigerant recovery equipment is available
Procedure
- 1Recover refrigerant from AC systemConnect the refrigerant recovery machine to the AC service ports. Follow equipment manufacturer instructions to completely recover all refrigerant from the system. Document the amount recovered for recharging reference. This step must be performed by a certified technician with approved recovery equipment.
- 2Disconnect battery negative terminalDisconnect the negative battery cable to prevent electrical shorts while working on the pressure switch electrical connector. Move cable away from battery post.
- 3Locate low pressure switchThe low pressure switch is mounted on the accumulator or suction line near the firewall on the passenger side. It has a single or dual wire electrical connector and threads into the AC line. Visually inspect the area and clean any dirt or debris around the switch.
- 4Disconnect electrical connectorPress the release tab and carefully disconnect the electrical connector from the low pressure switch. Note the connector orientation for reassembly. Inspect connector terminals for corrosion or damage.
- 5Remove old pressure switchUsing an adjustable wrench or 1 inch wrench, turn the low pressure switch counterclockwise to remove it from the port. Remove the switch carefully to avoid dropping debris into the open port. Have a shop rag ready to catch any residual oil that may drip from the port.
- 6Inspect and replace O-ringRemove the old O-ring seal from the switch port or from the old switch threads. Clean the port threads with a shop rag. Install the new O-ring seal onto the new pressure switch, ensuring it seats properly in the groove. Do not use oil or lubricant on the O-ring unless specified by switch manufacturer.
- 7Install new pressure switchThread the new low pressure switch into the port by hand until finger-tight to ensure proper thread engagement. Using the wrench, tighten the switch until snug. Do not overtighten as this can damage the threads or crack the switch body. Typical final torque is hand-tight plus 1/4 to 1/2 turn.
- 8Reconnect electrical connectorReconnect the electrical connector to the new pressure switch, ensuring it clicks into place securely. Verify the connection is firm by gently tugging on the connector.
- 9Reconnect batteryReconnect the negative battery cable to the battery terminal and tighten securely.
- 10Evacuate AC systemConnect vacuum pump to the AC system through the service ports. Run the vacuum pump for at least 30-45 minutes to remove all air and moisture from the system. The system should hold vacuum for at least 15 minutes after pump is shut off. If vacuum drops, there is a leak that must be repaired.
- 11Recharge AC systemUsing the manifold gauge set and charging station, recharge the system with the appropriate type and amount of refrigerant as documented during recovery. For 1970 AMC systems, original specification was approximately 2.5-3.0 pounds of R-12. If converted, follow conversion specifications. Monitor pressures during charging to ensure proper fill.
Reassembly
- Verify all electrical connections are secure and properly seated
- Ensure no tools or parts are left in the engine bay
- Check for any refrigerant leaks around the new switch using leak detector
Verification
- Start the engine and turn AC system to maximum cooling
- Verify compressor engages and cycles properly
- Check that low and high side pressures are within specification using manifold gauges
- Confirm cold air is blowing from vents at proper temperature
- Inspect new pressure switch for any signs of refrigerant leakage
- Verify pressure switch electrical connector shows no signs of looseness or corrosion
- Test AC operation through several on/off cycles to ensure switch functions correctly