Bendix AD-IP Air Dryer question..

Unloaders leaking in the compressor will cause this.

 

First, I don't mean to hijack here but I have a very similar problem. Just a little different, mine blows air directly out of the purge outlet port as soon as the governor calls for air, (turns the compressor on), this may last a few seconds or near a minute. I have (in order), replaced the governor, unloader valves, dryer, compressor. Almost no change at all. does not do it in the morning when cold, starts after a half hour or so. My next step is replacing the trigger line from the governor to the dryer, maybe deteriorated inside or kinked I don't know, will check that O ring also. Wondering if you checked that small line or if it could cause the symptoms you describe?

 

Another thing to consider in all of this is how close together the cut in and cut out pressures have become. In the days of 90psi cut in and 120psi cut out, these cycle problems were rare, now the cutin/cutout can be within 10-15psi of each other. This alone can cause problems.

 

Friend of mine always uses a high temp governor, may try one of those, but I doubt it is the problem

 

I have had trouble with the ADIS check valves, usually I install an in line check valve at the wet tank. The built in valve will bleed off the wet tank, which causes the d2 to cycle the compressor. Hence the in line valve, the replacement for the dryer doesn't seem to hold up.

 

First, if you have ABS your cut out is too low. It should be between 130-135 in order for the ABS valves to work properly during a ABS engaged stop.

Now on to the leak. Remove the air drier filter. On the top is a plastic tube with a o-ring in it. Remove it and see if the O-ring is in it. If not, get a valve rebuild kit. You have another one inside the inlet side of the drier (large hose that uses a 1 1/4" wrench, not the small one with quick connect or 7/8" fitting). If either of these o-rings are bad, you will get constant leak off. Since you said it only happens with truck running, that is the most likely cause. I change these valves at least twice a week. They are extremely common.

Here is diag process. Drier doesn't purge, but air builds and builds and builds, problem is governor. If purges and holds open as in constant blow out of purge, purge is bad. If constant purge over and over, problem is bad air line, bad unloader valve, or bad o-rings on one of the two small plastic valves. If you run a Mack with dual air driers, change all 3 valves in drier.

Now to refine more, if purging over and over with no air pressure drop, unloader valve is bad. If air pressure drops while vehicle is on and/or off, air line is leaking. If constant purge and air only drops while running, then valve inside drier is bad.

I home this helps you all with locating the problem.

 

I would think that higher rpm stopping the issue points to an unloader problem. The higher rpm moves more air and seats the unloader. Try your up to 1300 test and then fan some air out after you return to idle and see if problem reoccurs.

 

Im pretty sure it is platic valve with the bad o ring

 

bendix has had check valve issues for some time now since moving production to mexico.