Dryer purge every 15 seconds

[backyardwren]

Hi, I have a 1999 Itasca Freightliner chassis and the air dryer purges about every 10 to 15 seconds. I just cleaned it out and serviced it (new convalescent filter and desecant filter, new purge valve). I acquired the parts from Inland Truck Parts they looked up the parts using the VIN # from the chassis. I am just wondering if it is purging to often or is this normal? Just don't want to get stuck somewhere because something is not right that I could have fixed beforehand. Thanks in advance.

[BigDBright]

That's not normal. Assuming the new drier is working properly, the governor on the air compressor appears to be the problem. I don't know what they call them these days, but years ago when I was working on air brake systems they were called a 'D-2' governor. They are adjustable to regulate the max air pressure the compressor was putting out. What happens if you pump the brakes (parking brakes released to keep from 'compounding' the pressure on the rear axle) down using the foot brake until you're down to 80 pounds or so? Still cycle as it is building back up? I'm thinking the drier 'sees' high pressure and is trying to protect the system. Fair notice; it's been years since I've been in the industry and design of brake components probably have changed.

[Steve Ownby]

Originally Posted by backyardwren

Hi, I have a 1999 Itasca Freightliner chassis and the air dryer purges about every 10 to 15 seconds. I just cleaned it out and serviced it (new convalescent filter and desecant filter, new purge valve). I acquired the parts from Inland Truck Parts they looked up the parts using the VIN # from the chassis. I am just wondering if it is purging to often or is this normal? Just don't want to get stuck somewhere because something is not right that I could have fixed beforehand. Thanks in advance.

Since the problem appeared after the dryer service, I'm guessing there is some issue with the service that is causing this. I'm wondering if an O ring or gasket is out of place or leaking. Sometimes the old O ring particularly gets left in place & causes a seating problem. I know it's not pleasant but I would take the dryer back apart. You know the drill now so it will go quicker.

[backyardwren]

Thanks BigD and Steve.
The problem started before the dryer service and I serviced the dryer knowing it had not been serviced in a while. Just bought this motorhome in Feb. and was told the cycling of the purge valve wasn't normal. Guess I'll look into a governor and see if that fixes it.

[Steve Ownby]

Originally Posted by backyardwren

Thanks BigD and Steve. The problem started before the dryer service and I serviced the dryer knowing it had not been serviced in a while. Just bought this motorhome in Feb. and was told the cycling of the purge valve wasn't normal. Guess I'll look into a governor and see if that fixes it.

Do you have an air tank pressure gauge on the dash? If so watch it and see if you are getting a steady drop in pressure after each purge and then an increase in pressure after a few seconds building to another purge. If this is happening then you have a pretty substantial air leak somewhere.

[stink]

Old school truckers may agree but an air tank full of water could cause quick purge times. Have you drained your tanks lately? Drain cables may be in the right front wheel well just to the rear of the tire. Just air up the coach and pull the cables. Check for water under the front of the coach just aft of the front axle.

[LPD218]

Backyardwren,

My 2004 Freightliner was doing the same thing. I switched out the d2 governor, and put a lot of other parts into the issue. Finally I started isolating the air lines and charging the system with a compressor and found that I had a leaking 1/4 inch (grey) plastic line from the D2 to the dryer. The line had a large cut in it.

Freightliner helped by sending the schematics for my air system. I isolated the system with fittings I got from the hardware store and put them into the system with an air gauge on the air tank to look for leaks. I switched computers and my photos are gone, but I do believe the post is here on this site still.

Good luck!

[Hooligan]

Here's Dave T's earlier post... Hope it helps.
http://www.irv2.com/forums/f26/purgi...ng-179702.html

[rskrbina]

Check that the governor mount bolts are tight. They can loosen causing excessive purge. Hope this helps.

[BigDBright]

I've been thinking about this. Assuming there isn't a massive air leak with the engine off and brakes released, the issue just about has to be between the compressor and the wet tank check valve where the line comes into the tank from the compressor. In a system without the drier, the only parts between those two components are the governor lines (if the D-2 is remotely mounted), the D-2 itself, and the braided line going from the output of
the compressor to the wet tank. So, Rudy and Dave's suggestions have merit. Just be careful when checking the lines before the wet tank; the compressed air can be very hot and the braided covering (if equipped with that type of line) will cut you very easily if it's frayed. I'll trade you your issue for mine...LOL.

[backyardwren]

Well, I checked the governor bolts and they are tight. The tanks are dry and can't see any damage to the quarter inch plastic lines however I'm going to pick up fittings so I can pressure test them. Won't be able to do that till probably next week. Thanks for all the suggestion from everyone. I'll post what I find.

[bigdog]

My next project is replacing the dessicant and filter and I have ordered the parts for it from amazon,$134 plus shipping and sales tax. I got the directions from Hooligan and am all ready to head for it when the parts arrive. Then I started to read some of these posts and am waffling a bit. Nawwwww,being a longtime backyard mechanic,I am still thinking that I can still do it. I installed a trailer hitch on my Jeep Liberty,man those are some tuff bolts to loosen and reinstall. ( I broke my 1/2" torque wrench tightening them to 175# as they didn't want to tighten all the way in) and also changed the plugs on it. Boy,don't you just love those coils over the plugs.
So,I'll keep you advised on the servicing and hope that I don't find any leaks.

[bigdog]

Ok,here's what happened to my servicing. When I was replacing the E brake air pressure sensor,I did something sliding under the MH to my shoulder and couldn't do much lifting. I called several places to se if they would service it with my parts and 4 out of the five said no. The fifth,and last one called,Northstar RV repair in Bremerton, said sure,bring it in. I went to see his place and set up an appointment. Took it in on monday morning and they racked it right up and the tech had it done in about 45 minutes. This is the first time I have EVER taken my rig in and had them start on it right away,well except for the CAT shop in Fife,and the mechanic,not tech,worked on it till he was thru.It was a mess,all caked up with hardened oil and looked as if it had never been done. I looked at my service records and found that the time it was s'posed to be done,they noted thsat they didn't haver the parts and didn't do it. They also didn't verbally let me know,just buried it in the invoice as a no charge item. He did an awesome job of cleaning it all up and getting it back together and upon checking the heater,discovered that it wasn't working,so I have ordered one and will be installing it myself this weekend when it comes in. He did say that that was probably most of the reason it looked so bad as there was no heating of the unit. Since he only took 45 minutes for the job,he checked around the rear of the MH,tightened a few bolts on the exhaust system that had just been replaced,showed me a couple of things that will be needing to be done soon and recomended that I needed a tranny service soon also. Oh, and all this for $85 an hour. I will be going back there from now on.fer sher.