ISC, ISCe, QSC8.3, ISL, ISLe3, ISLe4 and QSL9 Engines – 012-999   Compressed Air System – Overview

Air Compressor

Several different air compressors are available for the engines covered in this manual. Both single cylinder (1) and two cylinder (2) modules are available.

The air compressors can either be turbocharged or naturally aspirated, depending on the configuration.

The air compressor can also be a low throughput torque or high throughput torque model, depending on the application.

Low throughput torque models have an SAE A rear flange (1).

High throughput torque models have an SAE B rear flange (2).

To make sure the air compressor does not contribute to engine vibrations, when installed, the air compressor must be properly timed on the engine.

The key factor which determines the reliability and durability of an air compressor in an application is the amount of time the air compressor is supplying air during the vehicle/machine operation, known as the duty cycle of the air compressor.

Air compressors are not designed to pump continuously and will generate a lot of heat when pumping, which is dissipated during the time the compressor is not pumping (called the unloaded operation).

Compressed air system maintenance/servicing can help minimize air compressor duty cycle and ensure reliability and durability of the air compressor. These item include but are not limited to:

1. Find and stop all leaks in the system. Air leaks can double or triple operating duty cycles. Close attention to correcting air system leaks is critical.
2. Checking the air compressor exhaust port, discharge line, and fittings for carbon build up. If the carbon buildup is greater than 1.6 mm [0.06 in], clean or replace as necessary.
3. Check the air lines and fittings between the outlet port of the air dryer and the first tank after the air dryer for any water or oil. The tank should be dry. If oil is present, replace the dryer desiccant and clean the downstream system and components as required.

Refer to the OEM manual for the vehicle for maintenance and service information for the compressed air system. For air compressor specific maintenance, see the Operation and Maintenance and/or Owner’s manual for the engine being serviced.

Air Compressor Cylinder Head

The air compressor cylinder head is cooled by engine coolant. The cylinder contains intake and exhaust valves to regulate air flow into and out of the cylinder head.

Most air compressor cylinder heads can be serviced without removing the compressor from the engine. This manual covers servicing of the cylinder head with the compressor installed on the engine. If there is internal damage to the air compressor, the air compressor must be replaced.

Prior to removing the air compressor cylinder, make sure to check if replacement parts are available. Some air compressor cylinder heads may not be able to be serviced separately from the air compressor.

The compressor operates continuously, but has a ”loaded” and ”unloaded” operating mode. The operating mode is controlled by a pressure activated air governor and the air compressor unloader assembly. The air governor can be located on the air compressor or remotely on the vehicle.

When the air system reaches a predetermined pressure, the governor applies an air signal to the unloader assembly, causing the unloader to either hold open or shutoff the compressor’s intake valve. This causes compressed air to stop flowing into the compressed air system.

As the system is used, the pressure drops. At a predetermined pressure, the governor directs an air signal to the compressor unloader assembly, allowing the compressor to again pump compressed air into the system.