A/C Diagnostic Procedure

1. Connect the A/C manifold Gauge Set to the high (discharge) and low (suction) service valves. Insert one of the dial thermometers in the center air outlet. Wet the gauze on the second dial thermometer with water, and tape it and the third thermometer in the air inlet to the A/C blower so that the thermometer bulbs are directly in the air stream. Place the fourth in the air stream 3 feet ahead of the car's A/C condenser.
2. Turn on A/C mode and blower to MAX positions; temp. to lowest position.
3. Warm up engine and set idle speed to 1500 rpm with A/C on.
4. Measure and record temperatures.
5. Determine relative humidity by observing where the readings of the two blower inlet thermometers intersect on the psychrometric chart on page 2. (The gauze-wrapped thermometer provides the wet-bulb reading.) Example: Your dry-bulb thermometer in the blower inlet reads 93~F, and your wet-bulb thermometer reads 65~F. On the psychrometric chart (relative humidity chart), draw a horizontal line at 93~, parallel to the 90~ line, and another line at 65~,parallel to the slanted wet-bulb 70~ line. Where they intersect, read the relative humidity from the nearest curved relative humidity lines.
6. Compare observed temperatures with data in tables below.
7. If observed data differ substantially from the values listed, then proceed to diagnose the system condition using the diagnostic charts on pages 4-7.
Note: ^ Pressure drops as blower speed decreases
^ Pressure is lower at lower relative humidity
^ Outlet temperature drops as outside air temperature drops