The compressed air system normally consists of a gear driven air compressor, an air governor, air tanks and all
necessary plumbing.
The Holset SS191B air compressor is an engine-driven, piston-type compressor which supplies compressed air
to operate air activated devices. The compressor operates continuously but has a “ loaded” and “ unloaded”
operating mode. The operating mode is controlled by a pressure activated governor and the compressor unloading
assembly. When the air system reaches a predetermined pressure, the governor applies an air signal to the air
compressor unloader assembly causing the unloader valve to hold the compressor intake valve open and com
pressed air stops flowing into the air system. As the air in the air system is used, the pressure drops. At a
predetermined pressure the governor exhausts the air signal to the compressor unloader assembly allowing the
compressor to again pump compressed air into the air system.
This air compressor is available in an air cooled or water cooled version, the only difference being changes to the
cylinder head to incorporate a water passage.
This air compressor is also available with or without a power steering pump housing.
Other brands of compressors may be used on the B series engine. Troubleshooting procedures are very similar
for these air compressors compared to the Holset SS191B. Refer to the specific air compressor manufacturer’s
manual for detailed repair information including torque values.
NOTE: The cylinder head and unloader components of the Holset SS191B air compressor can be serviced without
removal of the air compressor on many engine applications. This troubleshooting manual will cover servicing of the air compressor unloader components while the compressor is still on the engine. All other servicing of the air compressor internal components should be done after the compressor has been removed from the engine. Reference the SS191B Shop Manual, Bulletin No. 3810433, for detailed disassembly and assembly information of the air compressor.
The Holset SS296 single cylinder air compressor is an engine-driven piston-type compressor which supplies
compressed air to operate air activated devices. The compressor runs continuously but has a loaded and unloaded
operating mode. The operating mode is controlled by a pressure-activated governor and the compressor unloading
assembly.
The SS296,air compressor used on B series engines uses an (E-type) unloader. The Economy (E-type) unloader
system was designed to reduce pumping losses and engine boost pressure losses through the compressor intake
valve while operating in unloaded mode.
When the air system reaches a predetermined pressure, the governor applies an air signal to the air compressor
unloader assembly causing the unloader cap to seal off incoming air at the intake valve, and compressed air stops
flowing into the air system.
NOTE: System pressure must be maintained on the outlet side of the discharge valve to keep the discharge valve closed.
As the air in the air system is used, the pressure drops. At a predetermined pressure the governor exhausts the
air signal to the compressor unloader assembly allowing the compressor to again pump compressed air into the
air system.
Caution: Vehicles equipped with air dryers vented to atmosphere during unloaded compressor operation, A
using the Holset (E-type) air compressor, require the installation of an Econ valve to prevent excessive oil consumption. If the air system pressure is not maintained on the discharge valve during unloaded operation, air will be pumped
out of the compressor cylinder causing a low pressure (vacuum) condition to form in the cylinder. With the intake
valve sealed off by the unloader cap, and the exhaust valve being a one-way pressure actuated valve, no air will be allowed to enter the cylinder. When the compressor cylinder pressure falls below crankcase pressure, oil will
be drawn past the piston rings and pumped into the air system.
Other brands of compressors may be used on B series engines. Troubleshooting procedures are very similar for
these air compressors compared to the Holset SS296. Refer to the specific air compressor manufacturers manual
for detailed repair information and torque specifications.