Caterpillar 270 Air Compressor Caterpillar

Testing the Unloader System

In order to test the inlet valve, the discharge valve, and the unloader pistons, it is necessary to have access to compressed air. Assorted fittings and a soap solution are also required.

Testing the Pressure Buildup

Note: This test should be run with the engine and the air system at normal operating temperature.

1. Start the engine. Lower the air pressure in the system to 620.5 kPa (90 psi). Run the engine at 1800 rpm. Measure the cycle time of the air compressor. Record the cycle time of the air compressor from 689 kPa (100 psi) to the specified nominal governor rating.

2. Run this test three times and use the average time. Compare this time to previously recorded buildup times.

   Leakage from the unloader is demonstrated by the excessive cycling of the air compressor.

3. Lower the system pressure. Run the engine at 1800 rpm and allow the cutout pressure setting for the compressor governor to activate. Lower the engine rpm to low idle.

4. The compressor should remain unloaded for a minimum of 5 to 10 minutes. If the compressor cycles more frequently and the system does not have excessive leakage, replace the air compressor or repair the compressor unloader mechanism.