AIR DRYER AIR DISCHARGE...how many times is to many times.

fan hub leaking kysor and horton drive master both need air to turn off ie realease or freewheel but a large leak in context to this thread. I would expect fan to drive all the time.

 

fan hub leaking kysor and horton drive master both need air to turn off ie realease or freewheel but a large leak in context to this thread. I would expect fan to drive all the time.

 

so if i pull off the small line going to the dryer and wait for 15 seconds if it blows out air from that small hose then the governor is bad?
15 seconds or however long it typically takes for you to hear your purge valve on the drier dump. This means either the governor or unloader valve in the compressor is bad. Propobly going to be the unloader valve but i often change the governor first if it hasn't been changed for a while because it's cheaper and sometimes a bit easier. The unloader valve is also easy to change and not much more money depending on your compressor model. The valve is sold as a kit and can be bought at any heavy truck parts place.The compressor does not have to be removed to do this. There will be a small plate with a few small bolts bolting it to the top of the compressor. Remove the bolts and plate allowing you access to the unloader valve inside. Change out the valve, spring, o-rings etc with the parts that came in the kit.

if it doesnt blow air then its not the governor?
Correct, if you remove the line and after waiting for a minute or so and no air comes from the line it means your problem is not the governor or unloader valve. The purge valve on the bottom of the drier would be the item to change at this point. My guess is this is the least likely possibility, but if it is the culprit it's easy to change.

so whayt lets the governor know when to send discharge to dryer? Cut out pressure determines when signal air is sent to open the purge valve.

Here's a quick run down on these three parts of the system and how they work together.
Just like a piston in a truck, the compressor piston is always pumping whether the truck needs air or not. The unloader vavle (similar to a valve in the engine) controls if the compressor can make pressure or not. When the truck calls for air the unloader valve is closed and air pressure can be built. When cut out pressure is reached the unloader valve is opened so that no pressure can be built.
The governor controls the unloader valve position and tells it when to close or open. The governor does this based on system pressure which it senses through the other small air line that goes to it. The pressure at which the governor tells the unloader valve to close would be your cut in pressure, and the pressure at which it tells the unloader to open would be cut out pressure.
The purge valve is there to help the drier remove excess moisture from the system. Once cut out pressure is reached and the compressor is unloaded(unloader valve opened) a small amount of signal air is sent from the governor to the purge valve which tells the purge valve to open, which dumps a quick blast of air and condensation that the drier has captured from the system.
So i think your problem is somehow air is escaping down the signal line to the purge valve telling it to dump even when its not time. So i believe either the unloader valve is sticking or faulty, or the governer is at fault.
It certainly can be confusing but i hope this helps. Good luck!

 

I actually have pretty much the same problem this fella is having, and I have changed the governor two or three times, I have changed all components of the Air Dryer and i DO NOT have any detectable apparent leaks that you can hear, meaning my truck will sit overnight and not lose almost any air. I have been told that my problem probably is the unloader valves, now I have issues trying to locate those because of course on a Volvo engine with a Volvo compressor it is impossible to get to anything. So I am trying to figure out if anyone knows, to replace the unloader valves in a Volvo compressor with dual lungs ( or dual valves) do you have to replace the whole compressor? Or can those be just replaced.

 

I actually have pretty much the same problem this fella is having, and I have changed the governor two or three times, I have changed all components of the Air Dryer and i DO NOT have any detectable apparent leaks that you can hear, meaning my truck will sit overnight and not lose almost any air. I have been told that my problem probably is the unloader valves, now I have issues trying to locate those because of course on a Volvo engine with a Volvo compressor it is impossible to get to anything. So I am trying to figure out if anyone knows, to replace the unloader valves in a Volvo compressor with dual lungs ( or dual valves) do you have to replace the whole compressor? Or can those be just replaced. I have been told that I would have to replace the whole compressor??

 

This is why I always say if you have near 500,000 or 5 years on your air components, just replace them all. The cost of having to work on the part again is far more than just replacing the whole unit with a reman part. I have had this happen on almost a dozen truck on mine and friends. I have also had old compressors detonate then brake a camshaft, throw chunks of metal in to the engine, or strip teeth from the cam gears. It is not a huge expense if you replace all 3 at once.

 

I mean I got no issue with replacing the whole thing, I pretty much did... all my components other than the compressor are new, I have replaced the air governor like 3 times, the purge valve, the air dryer, all the air lines, now to replace the compressor on a Volvo truck with a Volvo compressor that has dual lungs, just for the part its $1300 and that is what I am trying to avoid, i mean I will do it if it can not be fixed by the unloader valve kit.

 

So you replaced the whole air dryer with a reman unit, not just the purge valve? We had one that we replaced the "only moving part" purge valve and it still short cycled. Once we replaced it with a reman air dryer it was fixed.

 

When the air dryer purges there is air in the line and at the unloaders. If you disconnect the line there will be air.
If one or both of the air guages are dropping then it is an air leak in the truck side of the system, if both guages stay at the max and the system cycles then the air leak is in the wet tank system only, that is the air compressor, possibly the thermatic fan, and possibly leaking fittings on the outlets of the wet tank, plugs and the drain valve.
With the engine off and the system fully charged feel in the front of the fan hub there is a rubber plug, in the hub button that the fan mounts to. Wet you finger and feel for leaks, soap test the seal area for leaks as well.
Remove the air intake to the compressor and listen for leaks from the unloaders. Air governors do not cause a cycling problem, if it is the problem the air would be coming from the exhaust port.