TROUBLESHOOTING AIR COMPRESSORS

Here are a few common problems found after Air Compressors are replaced:

• Pumping Oil
• Pumping Slowly
• Compressor knocking
• Compressor Blown Apart

Here are a few of the reasons that one or more of these conditions may exist.

Pumping Oil:
This can be caused by an oil return line that is too small or partially plugged. It will flood the crankcase of the compressor with oil and then the oil will come up past the rings and out the compressor discharge port.

A dirty intake filter or restricted intake will cause the compressor to try and draw air up from the crankcase because it can't get enough air threw the intake to adequately supply the compressor. This creates a vacuum in the intake and you will see the intake wet with oil when this occurs.

High crankcase pressure caused from engine blow by will push oil up pasted the rings while the compressor is in the unloading cycle an indication of this happening is also oil in the intake. There is an intake check value that will solve this problem and the problem of an intake vacuum created by the turbo. The part number for the one check value is SN3711aJ. What it does is it will hold 4 or 5 pounds of air pressure in the compressor cylinders while the compressor is in its unloading cycle, it pumps this air from one cylinder to the other, preventing any oil from coming up past the rings. It also holds the check value closed during the unloading cycle, which prevents any intake vacuum from drawing oil up past the rings during the unloading cycle. Any compressor that is pumping oil will not pump it out the intake while it is working because the intake values are closed during the compression stroke and the compressed air goes out the discharged port.

All air compressors use a certain amount of oil. This oil is discharged out the compressor discharge line, where it may collect and, along with the high discharge temperature, gradually turn to carbon. This is why it is recommended that you change the discharge line when you replace a compressor.

PUMPING SLOWLY AND COMPRESSOR KNOCK
When a system is found too be pumping up slowly there are a couple of things that should be checked before the compressor is removed. First, check the discharge line for restrictions. Excessive carbon build up will restrict airflow to the tank. The discharge line should slope downward (without traps) so any moisture and oil passing through the line will flow down into the air reservoir where it can be later expelled. A partially blocked discharge line will cause the compressor to knock because of the excessive pressure being built up in the head.

The second thing to check is that there are no air leaks in the system which would prevent the compressor from filling the reservoirs. This can be checked by removing the discharge line at the compressor and applying shop air to the discharge line. Without the engine running you can listen for air leaks throughout the entire system. Disturbing the discharge line can cause carbon in the line to break away from the inside of the line and plug it. Care should be taken to keep from bending or moving it around anymore than necessary.

COMPRESSOR BLOWN APART
Compressors that have a hole in the side of the crankcase are usually the victims of a plugged discharge line. As we talked about earlier water from condensation will build up in the low spot of the discharge line and then freeze blocking off the line. This happens more in the spring and fall because of the high temperature changes from day to night. There is more condensation in the line. On the highway the compressor is in the unloading cycle most of the time so the water will freeze because of the wind chill factor. When the discharge line freezes shut. The compressor builds up pressure in the head until the connecting rod breaks usually coming out the side of the compressor crankcase. Another problem is low engine oil or low oil pressure. When this happens the connecting rod bearing furthest from the oil supply line will be the one that burns out from lack of lubrication. These are only a few of the things to look for while trouble shooting compressor problems. There are a lot of different things that can cause problems so it is important to trouble shoot the carefully.