Dryer constantly purging

[Mario]

Update: Solved by replacing the dryer.

Last year, on my '91 M936A2, the air dryer started purging as soon as I turned on the truck (0psi in tanks).
One of the smart people told me to rotate the 3/8" bolt on the purge port (bottom), and it worked.
It happened again just now and I tried the same but to no avail.
I can push on the purge 'plunger' and make it stop dumping air, but that's obviously unsustainable.

I took the bottom assembly off and cleaned it. Other than the usual oil/grime on the outside (around the snap ring), the insides were very clean.
O-rings looked fine as well.
I put everything back together (sans the protective cover) and started the truck. Immediately the purge valve started dumping air. Please see the video: https://youtube.com/shorts/u1_TPpHUPLo
I don't know enough to troubleshoot it, thus asking for help from the experts.
I did watch a video where the dude was T/S similar issue and in his case, it was the unloader on the compressor that was feeding the purge assembly on the dryer.

 

[Mario]

I took a quick video:

M936A2 air dryer purging

youtube.com

 

[Russ Knight]

Time for a rebuild.

 

[Mario]

Time for a rebuild.

Please clarify.
Mechanically, what in the air dryer is causing this?

 

[simp5782]

Replace the dryer. They are junk. Even with a rebuild they will continue to have problems.

Go with an AD9. You will have to swap out the heater to 24v

 

[simp5782]

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Replaces multiple part numbers including 109685, 109685X, 065225, 065225X. Bendix Style AD-9 AIR DRYER. Specializing in Air Brake Components including Air Compressors. Air dryers. Air Valves. Air over Hydraulic Brake Devices.

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[Mario]

For right now, as in today, can I bypass it, or prevent it from purging altogether?

 

[simp5782]

For right now, as in today, can I bypass it, or prevent it from purging altogether?

Just hook the inlet and outlet lines together with a JIC union or bushing

 

[Mario]

Just hook the inlet and outlet lines together with a JIC union or bushing

So in the field, with limited tools, there is no way to bypass it?
I'm sorta thinking that it might be the unloader valve on the compressor, but I don't know shit about these things other than what I read and watch.

 

[Lukes_deuce]

So in the field, with limited tools, there is no way to bypass it?
I'm sorta thinking that it might be the unloader valve on the compressor, but I don't know shit about these things other than what I read and watch.

Its pretty easy to do with a pair of wrenches. Had the same thing happen to my air dryer. Just tied the inlet and outline lines together to get my home. These units are a wear item and need to be serviced or replaced.

 

[Russ Knight]

For right now, as in today, can I bypass it, or prevent it from purging altogether?

You might disassemble it and clean it to buy a little time. Completely depressurize the air system first. Remove the three 5/16 screws, then the cup. There should be a thick paper gasket between the cup and heater element. remove it and the heater element. You will need a pair of snap ring pliers to remove the snap ring that holds the purge valve in. If the purge valve won't come out get a 5 gallon bucket and fill it about halfway up or so with water and place it directly under the purge valve. Start the truck and stand clear, and the air pressure should force the purge valve out. Once you get it out, clean it as best you can, then lubricate the o-rings with silicon grease and re-assemble. It worked for me once, but the repair didn't last long. I'd do what Wes recommends for a long term fix.

 

[Russ Knight]

So in the field, with limited tools, there is no way to bypass it?
I'm sorta thinking that it might be the unloader valve on the compressor, but I don't know shit about these things other than what I read and watch.

If air is flowing continuously from the dryer purge, the valve is stuck open, or partially open. The compressor will not provide enough air to overcome the leak and your brakes will lock up.

 

[juanprado]

As dirty as that valve looks. The filter/decaissant is way over due to be changed.

 

[18operator]

I had that happen on my International dump truck. I took apart the unloader valve, there was a small screen filter in there that was gummed up pretty bad. I cleaned everything up with brake cleaner and reassembled. That was 8 months ago and its still working fine.

 

[18operator]

You should be able to bypass the dryer completely, just have to drain the air tanks daily so the condensation doesn't build up and rust out the tank.

 

[Mario]

Bendix style AD-9 Air Dryer 065225, 109685 ***NEW AFTERMARKET*** 1 yr warranty! | eBay

Replaces multiple part numbers including 109685, 109685X, 065225, 065225X. Bendix Style AD-9 AIR DRYER. Specializing in Air Brake Components including Air Compressors. Air dryers. Air Valves. Air over Hydraulic Brake Devices.

www.ebay.com

Bendix 24v Ad-9 Heater and Thermostat Kit 109579 for sale online | eBay

Find many great new & used options and get the best deals for Bendix 24v Ad-9 Heater and Thermostat Kit 109579 at the best online prices at eBay! Free shipping for many products!

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Thank you for the details and the links.
The guy is currently out of stock. There are plenty of other sellers, but none have the mounting bracket included in their listings -- I asked.
Do you know if the mounting bracket that's on the truck is the same as what the new dryer would require?
I don't want to frankenstein this, and I can certainly find a kit that has everything, but it's more money and I don't feel like wasting it if I don't have to.

 

[Mullaney]

Thank you for the details and the links.
The guy is currently out of stock. There are plenty of other sellers, but none have the mounting bracket included in their listings -- I asked.
Do you know if the mounting bracket that's on the truck is the same as what the new dryer would require?
I don't want to frankenstein this, and I can certainly find a kit that has everything, but it's more money and I don't feel like wasting it if I don't have to.

.
Like some of the other guys have already suggested - you can bypass the dryer SHORT TERM just until the new parts arrive or to get you "out of a tight spot". Just make sure that you drain the air tanks daily or several times a day if you are standing there beside the truck

Chances are that whatever replacement dryer you end up with won't fit the mounting bracket that you have. The holes might not fit either. Just use one or two of the holes you have, then get the drill and go to work. It's gonna require a sharp bit. Several of them actually. Start small. Maybe 1/8th inch, then go up from there - and if you have Horror Freight drill bits, go buy yourself another box of them cuz you're gonna need them.

 

[Mario]

I replaced the governor based on someone's suggestion.
It was quick and cheap.
That didn't help.
Next, the replacement of the whole dryer unit.

 

[Mario]

I ordered the complete AD-9 air dryer kit from eBay.
The unit arrived complete with brackets, and in perfect condition.
I did have to order a separate 24v heater as completed AD-9 kits with 24v heaters were much more expensive.
I removed the old unit and using the mag drill made quick work of drilling new mounting holes.







I did have to drill a clearance hole in the lower bracket to allow for the existing bold to clear, but once again mag-drill made quick work of it.

Connected everything and initial tests are positive.

Thanks to all the guys for the quick and correct diagnosis/suggestions.

 

[Mullaney]

I replaced the governor based on someone's suggestion.
It was quick and cheap.
That didn't help.
Next, the replacement of the whole dryer unit.

.
Have you tried pushing the palm of your hand onto the "exit" of the purge under (on the bottom) of the air dryer? Often times due to lack of maintenance or just general crud in the airlines - the little rubber flapper that opens and closes will get stuck open. Your palm on the exit will often times make it close...

Guess based on your next post (just above) you solved the problem with a replacement dryer.
Good For You!!