Figure 1: Cutaway 3D model of a car AC compressor.
Using a straight edge and a feeler gauge to examine the flatness error between cylinder head, cylinder block, crankcase and bottom cover, which should not be more than 0.05mm, otherwise, you should grind it. If there are cracks in the cylinder block and cylinder head through observing or knocking, replace them with new ones.
Use the cylinder gauge to check the wear condition of the cylinder. If the cylindricity error is more than 0.25mm and the roundness error is more than 0.08mm, you should bore and grind the cylinder. The boring and grinding operation shall be carried out according to the repair dimension, generally divided into five grades and each step shall be increased by 0.25mm.
When the cylinder is bored to the last-level repair dimension, you can repair it by reinserting the sleeve. When you insert the case, the interference of the matching shall be 0.05mm ~ 0.12mm.
Through visual inspection, if you find cracks on the crankshaft, replace it with a new one.
If the clearance between crankshaft journal and ball bearing is more than 0.02mm, you could repair the journal by chromium plating or surfacing welding, or replace it with new parts.
If the roundness error of the connecting rod journal exceeds 0.10 mm, you should ground the connecting rod journal or replace it. If the limit wear is exceeded, you must replace the connecting rod journal.
The piston connecting rod group includes a piston, a piston ring, a piston pin, and a connecting rod.
If the connecting rod is bent, you should correct it. If there are cracks, replace the connecting rod with a new one.
The new piston shall meet all technical standards. The matching clearance between the new piston and the cylinder is 0.03mm-0.09mm. When the fit clearance between connecting rod bearing and journal exceeds 0.12mm, use a new bearing instead.
Figure 2: Connecting rod group of a piston compressor manufactured by Kawasaki, including connecting rod, piston, piston pin, etc.
Check the elasticity of the valve pieces of the inlet and outlet valves, the return spring of the unloading valve, and the oil plug spring.
If the elasticity is weakened or broken, replace these parts with new ones. In case the seats of inlet and outlet valves are worn out with convex marks, you should replace the valve plate assembly and replace all sealing gaskets.
When the filter element of the air filter is dirty, you could clean it with a cleaning agent or replace it with a new one.
After reassembling the AC compressor, you should run and test it. The test can be carried out on a special test bench or engine.
Test the compressor on a test bench.
Carry out a low-speed running-in test without a cylinder head. Its speed should be 600 r/min and oil pressure not less than 147 kPa～196 kPa. Then carry out the high-speed running-in test without a cylinder head. The rotating speed is 1, 200 r/min. It is carried out to run in the working surface. At this time, there should be no oil accumulation at the top of the piston. The oil pressure is 196 kPa ~ 294 kPa.
Permit the inflation test. The rotation speed is 1, 200r/min. Install the head and tighten the fixing bolts according to the specified torque.
When the air pressure gauge reaches a certain pressure, the required time should meet the requirements. The maximum air pressure test speed is 1, 200r/min, and the operation time is 15 min. At this time, the maximum air pressure generally reaches 882 kPa.
Test the compressor on the engine that runs at the speed of 1, 200r/min～1, 350r/min.
You should observe the time required for the pressure to reach a certain pressure and the maximum pressure. The relationship between the pressure of the air receiver indicated by the barometer and the inflation time should conform to the inflation characteristics. At the same time, check the air compressor for oil leakage, noise, bearing overheating, and other faults.
When the engine stops running and the pressure is 686 kPa, the air reservoir pressure begins to drop and it should not be more than 19.6 kPa within 1min.
If it’s necessary to bore the cylinder, grind the crankshaft, replace the piston pin, and bushing, you should scrap and replace it with a new air compressor instead of repairing it.
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