Technician Handbook Air Conditioning for Collision Repair Normal System The chart above describes the pressures in a fully charged system given the ambient (existing) temperature in the test area. Because humidity places a higher load on the A/C system, pressures will vary within the range shown depending on the relative humidity. These pressures also assume adequate airflow over the condenser: Position an external fan to blow air through the front bumper opening, particularly on rear-wheel drive vehicles with a belt-driven fan.
(These pressures are also listed in the Vehicle Repair Manual in metric units of °C and kg/cm2.) Pressures It is normal for the gauge needles to fluctuate (change reading) as the clutch cycles ON and OFF and the heat load changes, but they should not swing wildly. In addition: • If the test pressure is below the ranges indicated, this indicates an undercharged system that cannot exchange heat efficiently. • Normal low-side pressure along with a much greater than normal high-side pressure indicates air in the system. • When both pressures are above range, the system is overcharged or insufficient air is flowing through the condenser.
• If both gauges show equal pressures in the 60-80 psig range, this indicates a fully charged system with an inoperative compressor. Additional conditions and specific component failures can be diagnosed based on gauge readings as shown in the Vehicle Repair Manual. • Correct refrigerant charge amount is listed both in the Vehicle Repair Manual and on an under-hood label, which also list the correct compressor oil type. It is useful to take note of what are typical pressures for your particular area and climate. 30 Collision Repair & Refinish Training SERVICE TIP