How Do I Get This Fitting Loose??

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I got the fitting loose today by using my die grinder to cut off the tube and the tapered part of the fitting and then cutting two very shallow grooves about 30* apart on the face of the hex. The fitting then came right off with a wrench.

I did nick the threads of the wall fitting slightly but these threads are compressed by the new fitting and the air seal is in the mouth of the fitting, so I don't think there is going to be any problem with leaks.

The bad news is that the system doesn't hold air any longer than before so my leak is somewhere else. Also, the fact that my wet tank has been bypassed probably causes the air supply to decrease much sooner.

I found a leak in the drain valve to the radiator shutter air valve and replaced it. In the process I found that the air part of the radiator shutter system works perfectly. I thought it was rusted open but it was just a small supply valve that was turned off. Now I need to find out if the thermostat part of the shutter system is working. The bus has always run cold so this is good news.

Thanks again for all the good ideas.