AC Hose - Low Side

Replace the low-side AC hose on a 1970 AMC Rebel Machine 390ci V8, which runs from the evaporator to the compressor suction side.

Warnings

Tools required

Parts

• Low-side AC hose assembly × 1 — Use OEM specification or equivalent for R-12 systems
• AC hose O-ring kit × 1 — Check for R-12 compatible seals
• R-12 refrigerant or EPA-approved substitute × 1 — Approximately 3 lbs total system capacity

Fluids

• R-12 refrigerant or approved substitute

Preparation

1. Park vehicle on level surface and engage parking brake
2. Allow engine to cool completely if recently run
3. Have AC system professionally evacuated and refrigerant recovered by certified technician with proper equipment
4. Disconnect negative battery cable
5. Verify you have the correct replacement hose for low-side (larger diameter hose)
6. Inspect new O-rings and ensure they are compatible with refrigerant type

Procedure

1. 1

   Locate low-side AC hose
   The low-side hose on the 1970 Rebel runs from the evaporator outlet (firewall area) to the compressor suction port on the passenger side of the engine bay. It is the larger diameter hose of the two AC lines. Trace the hose to identify both connection points and routing.
2. 2

   Remove hose at evaporator connection
   Using a line wrench, loosen the fitting at the evaporator outlet on the firewall. The fitting is typically 3/4" and may require significant force if it hasn't been serviced in years. Use a backup wrench on the evaporator fitting to prevent twisting the evaporator outlet tube. Remove the bolt and separate the hose from the evaporator. Cap or plug the evaporator outlet immediately to prevent moisture and debris entry.
3. 3

   Disconnect hose at compressor
   Locate the suction port on the compressor (typically on top or side of compressor). Use a line wrench (typically 7/8") to loosen the fitting while holding the compressor port with a backup wrench. Remove the connection and immediately cap the compressor suction port to prevent contamination.
4. 4

   Remove hose from mounting clips
   The low-side hose is secured with metal or rubber mounting clips along the inner fender and frame rail. Carefully release each clip to free the hose. Note the routing path and clip positions for reinstallation. Remove the old hose from the engine bay.
5. 5

   Inspect fittings and ports
   Examine the evaporator outlet and compressor suction port threads for damage, corrosion, or metal debris. Use a wire brush to clean threads if necessary. Inspect the sealing surfaces for scratches or pitting that could prevent proper seal. Replace components if damage is found.
6. 6

   Prepare new hose assembly
   Unpack the new low-side hose and verify it matches the old hose length and fitting angles. Install new O-rings on both ends of the hose assembly. Lightly lubricate O-rings with refrigerant oil compatible with your system (mineral oil for R-12, PAG or POE for R-134a conversions). Do not over-lubricate.
7. 7

   Route new hose
   Route the new low-side hose along the same path as the original, ensuring it does not contact hot engine components, sharp edges, or moving parts. The hose should have adequate clearance from the exhaust manifold, alternator, and accessory belts. Secure with mounting clips in original positions.
8. 8

   Connect hose to evaporator
   Remove the cap from the evaporator outlet. Align the hose fitting with the evaporator outlet and hand-thread the connection to ensure proper thread engagement. Once seated, use a line wrench to tighten firmly. Use a backup wrench on the evaporator fitting to prevent twisting. Tighten until snug plus approximately 1/6 turn. Do not overtighten as this can damage the O-ring seal.
9. 9

   Connect hose to compressor
   Remove the cap from the compressor suction port. Hand-thread the hose fitting onto the compressor port, ensuring proper alignment and thread engagement. Use a line wrench with backup wrench to tighten firmly until snug plus approximately 1/6 turn. Verify the connection is secure but not overtightened.
10. 10

    Vacuum test system
    Connect AC manifold gauges to the system. Attach vacuum pump to the center port of the manifold gauge set. Open both high and low-side valves and run vacuum pump for minimum 30 minutes to achieve 29-30 inches of mercury vacuum. Close manifold valves and observe gauges for 15 minutes. Vacuum should hold steady, indicating no leaks. If vacuum drops, locate and repair leak before proceeding.
11. 11

    Recharge AC system
    With system under vacuum, connect refrigerant container to manifold gauge center port. Open low-side valve only and allow refrigerant to enter system. The 1970 Rebel Machine AC system holds approximately 3 lbs of refrigerant total. Use a refrigerant scale for accurate charging. Do not overcharge. Add refrigerant with engine off until system reaches proper static pressure, then start engine and complete charging to specification while monitoring gauge pressures.

Reassembly

1. Reconnect negative battery cable
2. Verify all AC line connections are secure and properly torqued
3. Ensure hose is properly secured in all mounting clips with adequate clearance
4. Double-check that no tools or parts were left in engine bay

Verification

• Start engine and turn AC to maximum cold setting
• Verify compressor engages and cycles properly
• Check all connections for refrigerant leaks using electronic leak detector or soap solution
• Allow system to run for 10 minutes and verify cold air output from vents
• Monitor gauge pressures: low side should be 25-35 PSI, high side 175-225 PSI at idle with ambient temperature around 75°F
• Verify no unusual noises from compressor or hissing sounds indicating leaks
• Confirm hose does not contact moving parts or hot surfaces during engine operation

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