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It has been quite cold here(between 0 and 15 degrees). I have started my bus (GM PD4106) on a couple of the colder days and it started  and aired up fine. And yesterday I went on a 200 mile trip with no problems. But today when I started it (its around 40 deg) it didn`t want to air up.  I let in run for about 15 minutes and then aired up OK. I presume I had a frozen air line somewhere. From the compressor the air line goes to a discharge muffler. This also has a drain on it and when I opened it it did drain but didn`t seem like there was a lot of pressure there. Is it possible that the muffler can freeze up. The reason I suspect it is because it is in the engine compartment and it appeared as though whatever was frozen melted as the engine got warmer so that probably eliminates anything outside the engine compartment.

Thanks

Fred Mc.

any thing can get ice crystals in it..takes awhile to warm steel up above freezing especially if there is ice inside it.At forty degrees it would be like putting a glass of ice cubes in your refrigerator they don't melt fast.

Dump some dry gas in at the output of the compressor.

What is dry gas?

Oh...ummm...really?  http://en.wikipedia.org/wiki/Dry_gas (http://en.wikipedia.org/wiki/Dry_gas)

Gas line anti-freeze, alcohol.

Thanks. While I am familiar with methyl alcohol /gas line antifreeze (I grew up in Saskatchewan -40 deg below) I have never heard the term dry gas.

Must be a US thing.  Anyways, that will dispel moisture, but most of all, get you thawed out very quickly.

I think that "Drygas" was/is a brand name which may have fallen into general use.

Fred,

You didn't say, but if you open the muffler drain with the engine off there is little or no pressure, all the pressure is blocked by a check valve downstream of the muffler.