Air Dryer Safety Valve

[64MCI]

I've got a 1964 MCI MC-5 that won't air up.  After a few minutes of the engine running, the safety valve (not the normal purge valve) on the air dryer starts releasing pressure every few seconds.  The gauge on the dash stays at 0.  When I shut the engine off, I can hear a small air leak from a tank in the front, so I believe the compressor is working.

I first noticed the issue last winter and since it was below freezing, I assumed there was some water in the air system and it was frozen.  Today, it's 45 degrees outside and I'm still having the issue, so doesn't seem like it would be ice.  There is a wire coming off the bottom of the dryer that isn't connected to anything, which I'm assuming is for a heater.  I tried warming up the dryer and governor with a heat gun, but no luck with that.  I tried tapping on the governor a bit as well.

I have no idea when the air dryer was last rebuilt...but definitely not in the last couple of years that I've owned it.  I'm guessing I need to rebuild the air dryer and possibly replace the governor, but is there anything else I should try before going that route?  Anything else I should to try to diagnose?

It was working fine last week in similar weather and I've never had any issues in the summer.

Thanks,
Jed

[Tedsoldbus]

Hi Jed. I'm Ted. And I have no idea. I am a new guy too and just wait to feed on the responses of the guys that know this. They will give you ideas/solutions before you know it. Hang in there. It is always something, never nothing. This too will pass....and be fixed.

[Ed Hackenbruch]

Don't know where your air dryer is located, but check your ping tank and see if it is plugged up. It is the small one that says drain daily on it, mounted on the bulkhead wall. At least that is where mine was on my 68 5A. May have to run a stiff wire up into it to unclog it.

[luvrbus]

There is a valve past. the dryer that lets pressure into the tank if it is popping at the AD 2 dryer it is not passing the valve

[64MCI]

I rebuilt the air dryer and got a new governor from Luke, but I'm still having the same issue with my MC5...safety valve on the air dryer is popping after the bus starts and idles for 5-10 minutes.  I can hear a tank near the front of the bus filling up, so something is working. 

I noticed on the old governor that there is an exhaust port that doesn't have a line attached or a plug in it.  Any chance there's supposed to be a plug in there and it worked it's way out?

@Ed, the air dryer is in the back by the engine, so I *think* it's been moved from it's original location.  I have wires that are run from the tanks to the wheel wells that I can pull to drain the tanks, but none of them say 'drain daily' that I can see, so not sure which tank is my ping tank.

@luvrbus, if that valve isn't working, would it start popping right away?  It takes several minutes of idling before it starts popping. 

Also, does anybody know where the dash gauge reads pressure?  I'm guessing it's not the front tank since I can hear that one getting air and the gauge is reading 0.

Thanks,
Jed

[Ed Hackenbruch]

Your ping tank is probably mounted on the bulkhead on the right side of the engine, it is small and usually says drain daily. 

[Dave5Cs]

No plug in that one but you should have a line going to the air dryer from the Air governor.
Did you replace the air dryer desiccant only or also the purge valve on the bottom triangle thingy and the check ball valve in the bottom as well as the check valve in the top line big nut on the AD2 air dryer?

[64MCI]

Yep, there is a line from the dryer to the governor, which I thought might be plugged, but when I took it off, I could move air through it easily.

I replaced the desiccant, the purge valve, and the check ball valve.  My check ball valve is at the top, not the bottom though, so maybe I missed something there.  I'll take another look.

[buswarrior]

The top check valve typically just looks like a big nut at the connection, if you haven't changed that, do so, there's nothing else left to change now...

The safety valve opens at 150 lbs, so it takes a little bit of running, to get the pressure up inside the obstructed air drier, for it to start popping.

Follow the output pipe from the compressor, the discharge muffler will be an enlarged part of the line, hopefully with a line leading to an accessible place, out of the bottom, that the accumulated moisture and oil can drain to.

The noises you hear elsewhere are just to fool you, it takes an amazingly small amount of air to be sneaking past the obstruction, to make you think something is happening. Solid pipe also helps transmit noises. Evidence is the presence, or not, of significant air, not noises.

Keep going, you're getting closer!!

Happy coaching!
Buswarrior

[Dave5Cs]

Might check the air release valve itself. Had one of mine stick open before and just replaced it and it stopped doing it.