Compressor Unloader?

**joe9246** · 04.01.2012

Sometimes during acceleration I hear a sputtering air noise, it happens right after the air compressor reaches 125 Psi and the air dryer purges. I've been told it is the compressor unloader, but the noise is not coming from the compressor. It sounds like the noise is coming from under the cab. It's a 2005 International 9400i truck.

**rickybobby** · 04.01.2012

Originally Posted by joe9246

Sometimes during acceleration I hear a sputtering air noise, it happens right after the air compressor reaches 125 Psi and the air dryer purges. I've been told it is the compressor unloader, but the noise is not coming from the compressor. It sounds like the noise is coming from under the cab. It's a 2005 International 9400i truck.

My truck was doing the same... it was the unloader . i had it replace, for $100. Mine was sounding like it was coming from cab also.

**Heavyd** · 04.02.2012

It is still the unloaders in the compressor. Basically as soon as the air pressure has reached cutout pressure the governor sends signal air to the air drier to purge and to the compressor unloaders. If the unloaders are leaking a bit, or are a bit slow to fully unload the compressor you will get that sound. The compressor is still pumping, but now the drier purge valve is open. A few seconds of this sound isn't much to worry about, but it is a sign the unloaders are worn.

**joe9246** · 04.02.2012

How easy are the unloaders to change? Do you have to take the compressor apart?

**Heavyd** · 04.02.2012

If you have an ISX I think your looking at replacing the compressor cylinder head. Cat is serviceable on engine, it is a little valve assembly that bolts into the top the head on the compressor. I think it is just a matter of removing a few screws and replacing it.

**joe9246** · 04.02.2012

Its a ba-921 caterpillar compressor. There is a small metal plate on the top of the head with two screws, would the uploaded be under there? There is also a brass valve looking thing on top also..what is that?

**Heavyd** · 04.03.2012

Yes, I believe so. I am racking my brain right now, it has been so long since I changed one last. Those two screws aren't very big and are prone to seizing inside, be careful taking them out.