MC 7 Door AirLock Burned Out - Help!

[his196]

Good day all.
1st post, looking for a little help.
1971 MC-7.

Was sitting at (high) idle for about 30 minutes the other day with the door closed completely, and airlock 'cherry' knob pulled (so air-locked, as always when prepping to drive away).
When all of a sudden, from the door-latch area I hear a loud pop, whiz, bang as if someone was trying to open the door, and then pow, a loud pop, hiss of escaping air, and then a very bad burnt/burning smell with light smoke coming out of the latch/cylinder area.

I immediately shut off the bus, grabbed the fire extinguisher, and thankfully, no flames/fire.
But that bad, bad burning stench lingered for another 30 minutes.

Now, zero air goes to the latch cylinder, and the 'cherry' knob does absolutely nothing.

Also, when I went to the rear and opened up the passenger and/or driver's side engine bay doors to inspect the compressor, AND I turn the Master Switch on, I hear a loud (NEW) hiss of air at the compressor as if it's relieving pressure from somewhere new.

So, I've got two issues:
1.  What failed/shorted/burned out?
2.  What's going on back at the compressor that's related to #1?

Any help would be helpful.
I DO have my complete parts and maintenance manual, but haven't really started taking it apart to inspect behind the panels in the stairwell.

Any help would be greatly appreciated.

Gotta get the family back on the road.

~Chris B.

[chessie4905]

Give a call to Luke at U S Coach. He may have a replacement and be of help. He's  been helping bus nuts for years. 1-888-262-2434.

[buswarrior]

Did the front door operate correctly before? Airlock activated automatically with moving the door handle?
The bypass with the red knob just left alone?

The air in the air system has a nasty smell, if a fresh air leak opened up, are you familiar with that, vs a burning smell?

What is the condition of all the other electrical under the dashboard?

Find the new air leak down the back, we can't find it from here...

Post some pictures, if you get to some evidence

Happy coaching!
Buswarrior

[Ed Hackenbruch]

Don't recall any wires to or by the air lock on my 5A. 

[windtrader]

on my mc8 the air lock for the door has never worked and it shuts fine. Maybe in a rollover i'll get thrown out but not going to bother chasing down the air lock

[his196]

Did the front door operate correctly before? Airlock activated automatically with moving the door handle?
The bypass with the red knob just left alone?

***Yes, everything worked perfectly before this.

The air in the air system has a nasty smell, if a fresh air leak opened up, are you familiar with that, vs a burning smell?

***It was definitely a burning smell.  Very foul, and a bit of smoke came from latch area.

What is the condition of all the other electrical under the dashboard?

***All other electrical working find.  Under dash is fine.

Find the new air leak down the back, we can't find it from here...

Yeah, not sure why I hear an escape of air at the compressor now that I don't recall ever hearing before.  And it's only when we turn on/off the Master Switch.

Post some pictures, if you get to some evidence

Happy coaching!
Buswarrior

[ol713]

  Hi;
    Probably what you smelled,  was your selinoid  just quit.  When you operate the lock handels it  activates a selinoid in the spare tire
    compartment.  they are the same as your skinner valve that is on the firewall. That one activates your fast idle;
    As for air sound around the air compressor, that might be your governor on the compressor.  Let us know what you find.
                                                                Merle    (MC-7)         

[robertglines1]

door: drain all air pressure on coach.. It takes pressure to operate the locking system. Lack of air releases latch.

[Glennman]

I know that an air lock on the entrance door can be nice and gives a secure feeling. However, in the process of installing a sedan door in lieu of my double, air operated doors, I completely eliminated its air system. I now have a door that I can operate at any time, under any circumstances. Have you ever tried to open a door such as yours while underway? You can hardly push it open. The faster you go, the more difficult it is. It's not like you have a bunch of customers in the bus who may try to exit while driving. A good deadbolt is all that is needed (IMHO!).

[buswarrior]

The entrance door is sucked outward at speed.

The airlock is to hold the door tight against the door seals for a quiet journey, in a way that the closing mechanism can't.

It hasn't anything to do with security.

Happy coaching!
Buswarrior

[windtrader]

The adjustments on my door without the air lock seem to hold the door quite tight and solid. Not sure if it was adjusted out of spec to become really tight but there is a fair amount of force needed to get to to full close.