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Home >> GMC >> 1990 >> Forward Control 3.9 L >> Repair and Diagnosis >> Heating, Ventilation & A/C (HVAC) >> General Servicing >> A/C System General Servicing >> Charging A/C System
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Charging A/C System

NOTE: DO NOT  connect high side gauge hose to high side service port. Perform A/C charging service through low side only.
  1. System must be evacuated before charging. With manifold gauge set attached from evacuation procedure, start engine, but DO NOT  turn on A/C. With gauges and R-12 drum (inverted for liquid charging) connected from evacuation procedure, open low side gauge valve on manifold gauge set. Allow one pound of R-12 to enter system.
  2. When one pound of R-12 has entered system, turn A/C to NORM position with blower on high speed. Continue charging (liquid charging) until proper amount of R-12 has entered system.
  3. Close R-12 drum valve and continue running A/C system for 30 seconds to clear lines and gauges. Turn off valve on manifold gauge set. With engine running, disconnect low side hose and install service valve cap at accumulator. Perform leak test procedure.
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