Compressor Current Draw, Pressure Output & Leak Down Test

Fig. 28 Compressor Current Draw Test:

1. Disconnect compressor motor wiring harness connector.
2. Disconnect air line between dryer and right shock absorber.
3. Connect an air pressure gauge into the system as shown.
4. Connect an ammeter in series between the red wire terminal in compressor connector and a 12 volt power source. Connect a ground wire from the black wire terminal on the compressor connector to a good ground on frame.
5. If current draw to motor exceeds 21 amperes, replace compressor assembly.
6. When air pressure stabilizes at 120 psi, disconnect the positive wire lead.
7. Replace the compressor assembly if any of the following conditions exists:
a. Air pressure leaks down below 90 psi before it remains steady.
b. Output pressure builds up to less than 110 psi, then stabilizes.
8. If the compressor is allowed to run during this test until it reaches its maximum output pressure of 220 psi, the solenoid exhaust valve will act as a pressure relief valve. The resulting leak down, after the compressor is shutoff will indicate a false leak.