Cummins ISX Air Compressor Troubleshooting & Replacement

If your Cummins ISX is failing to keep pressure or build pressure, then you may have a failed air brake compressor.

Sometimes carbon can build up in the head and the unloader mechanism sticks. Tapping it with a hammer may help, but if not, then it’s time to change the compressor.

It’s not a difficult task to achieve if you have the right tools, skills, and a few hours of your time. Before you replace the air compressor, troubleshoot it first to ensure it’s not something else.


There are a few other issues that can make your Cumming ISX air compressor not work properly. Here are a few possibilities:

Power Source

Check the electric cables and the power source to the compressor. If the compressor isn’t working, make sure the power source is constant and steady.

Look for frays in the cables and shorts to the power. If you see there are frayed cables or shorts, replace them promptly.

Examine Air Intake and Air Filter

If you are noticing air buildup problems, check the air intake and air filter. If too much pressure is being built up or there is an oily discharge seen, there’s a possibility that the intake is clogged and/or you have a dirty filter.

If this is the case, replace the filter and remove blockages in the air intake. Check to see if this fixes the discharge or buildup issues.

Examine the Outside of the Compressor

Carefully examine the outside of the air compressor. Make sure it’s free from cracks for air to get out of.

This can lead to either the case cracking open or air expulsion. If there’s a crack, it needs to be replaced or professionally sealed.

However, if you see condensation on the case, then the humidity could be the culprit. This will cause issues with the motor.

If this is the case, the compressor should be moved to an area that has less humidity.

Check the Belts

If you hear noise coming from the compressor, it may be a belt. It could be loose, frayed, or getting caught on something. Replace the belt with a new, tighter one and try again to see if the noise stops.

Check the Air Valve

If you are losing pressure, it could be from a faulty air valve. Let the compressor build up air pressure then close the safety valve.

Put your hand on the opening to see if the air is escaping. If you feel air coming out of the valve, replace it.

Check for Oil in the Compressor

If you notice oil leaking from the air compressor, this could cause an oil circulation shortage within the compressor. This will lead to a buildup of excess heat and the compressor could lock up completely.

If you notice oil leaking from a crack, seal it in the oil pain and replace the oil in the compressor. If the repair didn’t work, it’s time for a new air compressor.

Removing & Replacing The Air Compressor

If you aren’t able to fix the issue you are having with your Cummins ISX air compressor, then it’s time for a replacement.

They aren’t overly expensive depending on where you get them from. There are a variety of online stores that offer them with and without the gaskets.

Step 1

Remove the components leading into the compressor. Remove the main airline feeding the dryer. It may stick a little, so hold tight.

Step 2

Remove the line for the governor. This line is very easy to remove, but also delicate so proceed carefully.

Step 3

Remove the line for the air intake. You’re going to need a large crescent wrench to unscrew the intake bolt.

If you can’t get the bolt off, you can spray it with PB Blaster or any kind of spray that will help loosen the bolt.

Step 4

Remove the power steering pump. There are two bolts, one on the top and one on the bottom of the pump.

Remove those and wiggle pump a little and it should pop right out. You can set that aside.

There will be no fluid leaking out since it’s an enclosed case and uses the gear on the back of the compressor to operate.

Step 5

Remove the bolts holding the compressor in. There are two bolts, one on top and one on bottom of the front part of the compressor.

They should be generally easy to remove.

On the front of the crankcase is a bolt as well. It’s a very long bolt that goes right through the front of the compressor. Remove that.

There are two bolts in the back of the compressor that needs to be removed also. There will be 5 bolts altogether, all of which are threaded.

Take these out before removing the coolant lines.

Step 6

Remove coolant lines. You’re going to need a bucket to catch the leaking coolant.

A lot of people will wrap rags around the lines after to avoid small dribbles of fluid until they are ready to be put back on.

You can tilt the compressor towards you once the bolts are out so you can reach the fittings.

Step 7

Remove the compressor and replace it with the new one. As you’re putting it back on, look for an X on the gear on the front of the compressor.

Line the X up with the notch. If you cannot locate the X, call the manufacturer.

It would probably be easier to look for a compressor with the X before you buy it. From there, work backward and your new compressor should be up and running.


And there you have it, that’s how you diagnose and replace a faulty air compressor on a Cumming ISX. This is a relatively easy fix and you can find the parts online.

You will more than likely need new gaskets. You can buy them separatelyor you can purchase the compressor with the gasket.

Most people will just replace the gaskets anyway since they tend to deteriorate over time.

      Residential & Commercial Air Compressors