NOTE: The below clean and inspect steps are only to be completed if the air compressor cylinder head was
removed as part of another repair.The air compressor cylinder head does NOT need to be removed if the
unloader and valve assembly are determined to be stuck/ seized. Refer to Procedure 012-003 in Section 12.
Inspect the cylinder head for signs of an external coolant leak. A large coolant leak from the air compressor cylinder
head will have blistered/removed paint and/or have a white deposit build up.
If a large coolant leak is observed, the head should be rebuilt with a gasket kit. Refer to the Cylinder Head Gasket
Kit in the Install section.
Inspect the unloader valve plate and cylinder head for deep scratching or scoring. If the cylinder head is
scratched or scored deeply, it must be replaced.
Verify that the unloader piston is in the proper orientation and operates properly. If, upon inspection, the unloader piston and plate are stuck open, exposing any area of the relief chamber, carefully remove the unloader plate from the unloader piston pinions.
NOTE: The unloader piston and plate must always default to the fully closed position.
Place a few drops of automatic transmission fluid into the unloader piston bore. Coat the front and back side of the
piston with fluid.
Use a stiff wooden handle to apply pressure to the unloader valve against the spring. Slide the unloader piston through the full range of rearward travel. When the spring is fully compressed, quickly let the pressure off,
allowing the spring to drive the piston back to its closed state. Repeat cycling the unloader piston in this manner 5
to 10 times.
If the unloader piston continues to demonstrate any resistance to movement, or slow response while returning
to the default closed position, the cylinder head must be replaced.
NOTE: The above steps can be completed without removing the air compressor cylinder head from the air
compressor by using the Air Compressor Cleaning Kit, Part Number 2882280. Refer to Procedure 012-003 in
Inspect the unloader channel and governor supply port, as well as the unloader piston, for signs of rust.
NOTE: Rust present in the unloader channel and/or governor feed port indicates that either the air dryer has
malfunctioned, or improper draining of the vehicle air tanks. Use the following procedure to check the air
governor for proper operation. Refer to Procedure 012-016 in Section 12. Refer to the OEM service manual for
troubleshooting the air dryer, as well as proper maintenance intervals for the vehicle compressed air tanks.
Inspect the intake and discharge ports for heavy carbon buildup. Use the following procedure for proper reuse
guidelines. Refer to Procedure 012-003 in Section 12.
While the air compressor cylinder head is removed, inspect the rotating components and the cylinder bore of
the air compressor for damage. Refer to Procedure 012-014 in Section 12.