Originally Posted by Versatile
Started bus the other day when it was 15' above. Started right up and the brake light came on. Frozen. Waited until to day and abouut 35 deg.Opened the drains on 2 tanks and go nearly nothing as to moisture. Removed no.1 supply line and dumped 2 cap fulls of Air brake antifreeze into it. At same time i cleaned and thread taped the brass fitting coming off the compressor.
Started bus and red light still on 10 minutes later. 20 minutes or so red light still on but brakes are free.
What should i have done?
Well, I'd say you should have done a little more troubleshooting. Some brake systems *REALLY* do not like the air-brake antifreeze; something about mucking up the valves in the rear (or trailer) brake control modules.
My *FIRST* question would have been, do you actually have air pressure in one tank or both? Never mind what the gauge says ... because the sensors can fail or freeze, giving you a false reading. My last Volvo would do this on the secondary tank when it was under 32 degrees ... and would continue giving a false reading until the truck was turned off and restarted (we never diagnosed why it did this, as it was much easier to simply do a reset, for no more than it occurred).
Second, once you've established there is no air pressure ... and you've given the system some time to build up ... some (many?) air systems take longer when cold to build up pressure. It should have reached enough to turn off the red light in under 10 minutes. There's a chance of moisture being in the system, or more likely, something sticks in really cold weather.
What is (was) your air pressure showing? Often brakes will release between 40-60 PSI, which is under the threshold for the warning light. Are (were) you losing air pressure? Any audible leaks?
Air tanks should be drained on a regular basis - at least at the end of every day of driving. For a bus on an active school route, this would be 5 days a week. For us, maybe much less often, but that makes it all the more important to be done. How much moisture do you get the first time you drain the tanks? (I think you said minimal-to-none.) How much on a daily basis?
I realize it was really cold, and to be honest, I wouldn't have wanted to mess with it at that time either. Often air brake systems have issues when it's "not cold", which are really only much more evident when temperatures drop below freezing.