Building air problem

[JAsaro]

So I’m having a problem building air I replaced the governor and the air dryer the air dryer is a bendix AD-IS I know those are known for problems I sprayed the WD-40 into the unloader valve still no change I have to read the engine between 12 and 1500 RPMs in order to build air it’s fine rolling down the highway it’s just when I come to a stop there are no air leaks I’ve already checked I’ve been having this problem for a few weeks the only other thing I can think of is the air Compressor I could replace the head for $900 and change or replace the whole air compressor for 1100 and change that’s what I was quoted from my dealer
Cummins isx15
2250

[Coronado126]

It sounds like you've done pretty much all you can do to troubleshoot the system. Have you verified the airlines to the governor, dryer, compressor, air tanks and back are clear and not obstructed?

When you have the RPM at 1100 building air pressure, how long does it take if you time it with a stop watch? DOT says 45 seconds maximum from 85 to 100 PSI but it should be MUCH faster than that.

Something I do to check a compressor that I believe to be super weak, I will take the discharge hose off the compressor when the engine is not running, and then start the engine and leave it at idle, and cover the discharge fitting with my thumb. If I can keep my thumb over that fitting and it not push my thumb off the fitting with air, than that compressor is weak.

I would not bother with changing the head with that small of a difference in price between the complete assembly. That way you'll have an entirely new compressor. Was that parts only, or installed?

[JAsaro]

(11-23-2020 )Coronado126 Wrote:  It sounds like you've done pretty much all you can do to troubleshoot the system. Have you verified the airlines to the governor, dryer, compressor, air tanks and back are clear and not obstructed?

When you have the RPM at 1100 building air pressure, how long does it take if you time it with a stop watch? DOT says 45 seconds maximum from 85 to 100 PSI but it should be MUCH faster than that.

Something I do to check a compressor that I believe to be super weak, I will take the discharge hose off the compressor when the engine is not running, and then start the engine and leave it at idle, and cover the discharge fitting with my thumb. If I can keep my thumb over that fitting and it not push my thumb off the fitting with air, than that compressor is weak.

I would not bother with changing the head with that small of a difference in price between the complete assembly. That way you'll have an entirely new compressor. Was that parts only, or installed?

It will hardly build air at 1100 it needs to be 1350/1500 it build I’ll try the thumb on the compressor tomorrow it definitely takes longer than 45 seconds

[JAsaro]

(11-23-2020 )Coronado126 Wrote:  It sounds like you've done pretty much all you can do to troubleshoot the system. Have you verified the airlines to the governor, dryer, compressor, air tanks and back are clear and not obstructed?

When you have the RPM at 1100 building air pressure, how long does it take if you time it with a stop watch? DOT says 45 seconds maximum from 85 to 100 PSI but it should be MUCH faster than that.

Something I do to check a compressor that I believe to be super weak, I will take the discharge hose off the compressor when the engine is not running, and then start the engine and leave it at idle, and cover the discharge fitting with my thumb. If I can keep my thumb over that fitting and it not push my thumb off the fitting with air, than that compressor is weak.

I would not bother with changing the head with that small of a difference in price between the complete assembly. That way you'll have an entirely new compressor. Was that parts only, or installed?

Yes I checked all the air lines

[hhow55]

Mr Rawze recommends replacing compressor 800k

[Signature620]

Sounds like a leaking air compressor discharge line. Spray it with soapy water with the engine running.

[JAsaro]

(11-23-2020 )hhow55 Wrote:  Mr Rawze recommends replacing compressor 800k

The truck only has 435000

[JAsaro]

(11-23-2020 )Signature620 Wrote:  Sounds like a leaking air compressor discharge line. Spray it with soapy water with the engine running.

Did that no air leaks on truck at all

[DVT873]

What compressor is it? Tangled with an older Holset a while back. Problem ended up being a broken spring. Broke in about 6 places. That design had a sliding plate and reed set up of some type. Spring was supposed to close the plate when it was time to work. It couldn't push it all the way closed...The rebuilds are a real crap shoot today. Doesn't matter whose it is. FWIW most actual compressor problems are in the head regardless of design. That might be why a head is alone is usually half the price of the compressor. Depending on how it sits in the frame changing the whole compressor can be a time eating PIA.

On a slow air build up best way IMO is unhook the discharge line at the compressor and plumb it to shop air. You will hear any leaks much better with the engine off. Remember your gauges don't show you what is happening in the first or "wet" part of the system. You can tee a gauge in if you really want to see. Airdryers cause their own share of problems.

Check the elbow fitting coming out of the compressor. They can carbon up and restrict the flow. Rare but not real rare.

Does the dryer purge or spit off constantly at idle? If it does there is a leak somewhere, usually in the "wet" part of the system, that is not gauged.

Something else I don't like. To save a buck all the OEM's plumb the compressor into the engine air intake system. This means the compressor is trying to get air from the same place as the engine. Usually on the intake side of the turbo. Unless it is fed off the boost side of the turbo, and very few are. Had a talk with a Bendix rep once. Very diplomatic guy. Left me with the impression that Bendix thinks sharing with engine is bad idea.

If I ran a truck two of many things I would do is add a gauge to the wet side and put a stand alone air filter on the compressor. Another thing would be to figure out what I needed to bypass the air dryer. On a nice warm sunny afternoon. Not at 2 am on the side of the road in a snow storm. Figure that out in advance and you'll never need to do it!!

Just my opinions. Worth what they cost most times!