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Compressor / Spitter Valve / Govenor Chase


msholl52
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2001 CH613 E7 300 - Truck began blowing off once every 30 seconds or so, so I did an air system service...new dryer, new spitter valve, cleaned housing and mount, new govenor, checked govenor lines (not mounted to compressor). Symptoms continued, replaced check valve in primary tank, symptons continued. At this point began to sniff around on the interwebs to see what I am missing, and came across the "unloader" option and tested to see if this could be the problem - removed 1/4" line that runs from compressor to dryer at 120psi and there WAS air coming out of the line - so I called Mack to get an unloader kit. They told me there is no unloader kit and i need a new compressor. I find this SO hard to belive. Its a Wabco 8235-S9111530557. Am I missing something? Are there kits out there that I am not being told about...anyone have any similar experiences? Thanks.

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When diagnosing this type of issue I install a gauge into the wet tank and a gauge into the unloader port on the governor. The wet tank is the signal source for the air governor. When air pressure drops in this tank then the air gov. dumps the air psi to the compressor and dryer purge valve so the compressor can rebuild the air psi. Once max psi is achieved the air gov. sends an air signal(system air psi) to the compressor and dryer purge valve. The air compressor unloads and stops building air and the dryer purges and dumps air within the dryer and line from the compressor.

The purpose of the gauges is to see where the air loss is coming from. When the dryer purges, do you loose air in the wet tank or on the unloader signal? If you loose air psi in the wet tank I would look at leaking lines, bad check valves and so forth. Once the dryer purges there should be no air coming out the purge valve. If there is air coming out the usual culprit is a bad discharge check valve on the dryer. If you are loosing air psi in the signal line(unloader), Either a leaking line or fittings, bad purge valve or air compressor head. A bottle of soapy water and a quite shop will help a lot.

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.........so I called Mack to get an unloader kit. They told me there is no unloader kit and i need a new compressor. I find this SO hard to belive. Its a Wabco 8235-S9111530557. Am I missing something? Are there kits out there that I am not being told about...anyone have any similar experiences? Thanks.

The Wabco air compressors don't have "unloaders" like other compressors. Everything is contained within the head assembly. If there are any issues with building air and it is not passing oil then replacing the head is an option rather then the whole air compressor.

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