Air Dryer Question

[Glennman]

Those heaters don't heat till the temperature is below 38 degrees then it is automatic makes one hard to test, some people use the 12 v tap on the MCI and new wire and don't change the heaters, I change the heaters, I bought 3 off Find it Truck Parts a few years ago for less than 50 bucks     

What I did was follow the manual's test procedures. I put the device in the freezer and tested the ohms, then I heated it to 100 degrees and tested it again. There was no difference. According to the manual, it's supposed to go from around 6.5 to over 1000 ohms. Mine had no difference at all, as it stayed at 6.5 (the warm amount) and didn't change at all when I froze it.

[Glennman]

Ok, so I retested the heater with a real test! I pulled the heater element and snap disc out of the purge valve housing. It's amazing that they got all that in there! I checked the snap disc by heating it up and then cooling it down. You can actually hear it engage. No continuity when warm, then after it snaps, it has continuity (after pulling it from the freezer). Then I connected 24 volts to the little element. It has a ceramic covering about the size of a pencil, is about 2 inches long, and gets hot when applying 24 volts.

I already ordered a rebuild kit from NFI. If it includes everything I need, I'll go with that. However, if it doesn't include a new check valve (I viewed a check valve at Fleet Pride today in it has a spring loaded device inside it, unlike mine that has nothing in it), then I'll pick up Fleet Pride's 12v AD-9, install my heater in it, install 1/2" to 3/4" port adapters and be done with it.

[Glennman]

Just to close this out for now in case anyone cares, I finally got the air dryer put back together. I ordered a new check valve besides the rest of the plunger kit. The plunger kit came with the heater element and the plunger already assembled and installed in its housing. That part was pretty cut and dried. It came with a filter too.

My main question regarding the check valve was answered. I ordered a new one, and lo and behold, it had an actual check valve inside it (if you recall, the old one was only a brass fitting with nothing in it. It must have come out during a service at some point). So, now it's all assembled, but I have yet to check it for leaks. Every time I climb under the bus I find something new. Climbing out yesterday after installing the dryer, I noticed some cracks in the brake linings that I didn't notice earlier. Now the bus will be on blocks for another 2 weeks while I install new shoes (relined) and brand-new drums.

[luvrbus]

You should check the MCI air schematics for your serial number not all applications used the check valve on the discharge port with the AD-9, some check valves were installed at the tank,Van's H-40 Prevost AD-9 just had a fitting on the AD-9 discharge port.I don't know what difference it would make but I used the fitting and left the check valve on the tank

[windtrader]

Every time I climb under the bus I find something new.
[/size]
[/size]Isn't that so true! These old buses are never 100% ship shape. There is always something that is old and needs maintenance.

[Glennman]

You should check the MCI air schematics for your serial number not all applications used the check valve on the discharge port with the AD-9, some check valves were installed at the tank,Van's H-40 Prevost AD-9 just had a fitting on the AD-9 discharge port.I don't know what difference it would make but I used the fitting and left the check valve on the tank

Thanks luvrbus, I'll check for that next week when I get back under the bus, since I still have it on blocks anyway. The local tour bus outfit ran a copy of a manual off on the AD-9, but it was from a '98 DL3. It included a breakdown of the AD-9 components with an actual check valve in it. I'll check the tank for any kind of a check valve on it. I'm assuming you are speaking of the (2) tanks that are near the dryer (?).

[Dave5Cs]

Clifford sent you a PM for the wife.
Dave

[Glennman]

Clifford sent you a PM for the wife.
Dave

I don't see a pending PM anywhere (?)

[luvrbus]

Dave sent the PM to me

[Glennman]

I finished intalling the air dryer, as stated in a previous post. However, based on luvrbus's comment on the possibility that the check valve on the bottom of the air dryer may not have been installed (or functional. The fitting was there but it was hollow allowing air to pass both ways) due to a check valve at the tank instead. I did more research and also finally got back under the bus today, and indeed, there is an inline style check valve between the two tanks. My research tells me that one of the two tanks adjacent to the air dryer between the front wheels is supposed to blow off with the air dryer. This certainly does sound right. When the air dryer pops, there is quite a bit of air that comes out, more than what the dryer holds, so it appears to be designed to blow off the "wet tank" (one of the two) with its purge.

All that being said, I'm going to put the old hollow fitting back in, since it appears that it was designed to work that way. Nothing like creating a problem where there wasn't one to start with. It appeared to function just fine before I decided to take it all apart. At least now I have a new filter and purge valve. I feel pretty good about that, and I did receive an education working on it all! Thanks everyone for all your help. If I have any problems when I fire it up, I'll let everyone know. That won't be 'till probably next weekend, as I'm in the process of installing new brake drums and shoes in the meantime.

[luvrbus]

I finished intalling the air dryer, as stated in a previous post. However, based on luvrbus's comment on the possibility that the check valve on the bottom of the air dryer may not have been installed (or functional. The fitting was there but it was hollow allowing air to pass both ways) due to a check valve at the tank instead. I did more research and also finally got back under the bus today, and indeed, there is an inline style check valve between the two tanks. My research tells me that one of the two tanks adjacent to the air dryer between the front wheels is supposed to blow off with the air dryer. This certainly does sound right. When the air dryer pops, there is quite a bit of air that comes out, more than what the dryer holds, so it appears to be designed to blow off the "wet tank" (one of the two) with its purge.

All that being said, I'm going to put the old hollow fitting back in, since it appears that it was designed to work that way. Nothing like creating a problem where there wasn't one to start with. It appeared to function just fine before I decided to take it all apart. At least now I have a new filter and purge valve. I feel pretty good about that, and I did receive an education working on it all! Thanks everyone for all your help. If I have any problems when I fire it up, I'll let everyone know. That won't be 'till probably next weekend, as I'm in the process of installing new brake drums and shoes in the meantime.

I kind of figured that was the reason because on the later buses the ping(wet) tank was moved closer to the air dryer with a check valve, Bendix lists a parts number for the pass through valve 

[Glennman]

Exactly luvrbus! Thanks to you I looked deeper, located the pass through check valve and now I've removed the new check valve and installed the old fitting back where it belongs. Thank you!