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Discussion Starter #1
Takes at least 5 minutes for the air gauge to come all the way to loaded pressure in cold weather.(-20 to -30C) This is on a hay rack triaxle log trailer.

I've cleaned around the leveling valve, and cleaned around the bottom of airbags. Could this be caused by a stiff or seizing up suspension? Once up to pressure, about 70 psi, the air pressure reading stays consistent. The last 10 psi comes up very slowly.

There is also a digital readout in the cab and this takes the same amount of time to reach actual loaded weight.
 

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Levelling valve freezing up? If not I would have to think it’s a symptom of cold weather.. if the suspension was seizing up it would act as if you have a heavy load on it and have higher pressure on it
 

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Discussion Starter #3
Just replaced the leveling valve. Will see what happens on the next load. We kept things at home during this -30C and colder weather.
 

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My guess is you a partially frozen air line somewhere. Undo the supply line to the leveling valve and see how much air is coming out, probably won't be much. Take a hair dryer or heat gun and follow the line back and warm up any spots where it sags down. Alcohol might help in the short term but once there is enough water laying in the line it will keep giving you issues, best to get it out of there. Be careful around the open air line when you do this, the chunk of ice can come out of there like a bullet.
 

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Discussion Starter #8
Thanks for the replies. Have good air volume to the leveling valve. We put air brake antifreeze in the system. Also has a sniffer system.

What does the pressure protection valve look like? That's got me thinking.
 

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Marvel Mystery oil was a product that someone who worked on oil rigs and as well had trucks claimed it worked well in air systems, that along with some airbrake antifreeze may help. I know trailers tend to get neglected as far as draining the air tanks and if the air dryer is in good shape it usually doesn't accumulate. It does seem odd that it works ok in freezing temps but not when it gets colder yet, most likely a valve issue somewhere in the system assuming you are not losing air and have barely enough tank pressure to release the spring brakes. YHMARK mentioned a protection valve right on the trailer supply tank, I didn't realize there was a unit like that back there but found some comments in a trucking forum that mentioned that very valve and that in some cases it was allowing the proper pressure to the brake pots but malfunctioning and not allowing any or limited air to the leveling valve. **** happens and quits when it gets cold though when it comes to equipment, that's for sure.

Is it working now, and now you have a new valve as well and put in the alcohol so you may still not have it solved, oh the joys.

I looked up the Haldex catalog and I think the valve on the tank may look similar to these units as I gather they are designed to shut off the air supply to the suspension if that system has a massive air leak to maintain a minimum tank pressure for the brakes. Look on pages 19-89 to 19-91
 

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The pressure protection valve won’t let air to the suspension till the system reaches a certain psi. The same as in the truck Where certain things won’t work till there is enough pressure
 

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The weird part is that eventually it would pressure up the suspension but lagging is my understanding, so some air was being fed into the air bags rather then none but what was limiting the flow, lack of tank pressure due to upstream issues, the protection valve sticking/frozen, or the ride height valve sticking or icing up etc.
 

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Could you plumb in an air gauge to trailer tank? You could see how fast it would air up then. You would know if the problem is getting air to the trailer or if it’s a problem getting to the suspension.

could also be a problem in the truck system no building air fast enough.
 

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That was what I was thinking before also, T into a fitting out of a tank port and run it to the level gauge box and install another gauge in it so it would always be easy to confirm trailer tank pressure.
 

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Takes at least 5 minutes for the air gauge to come all the way to loaded pressure in cold weather.(-20 to -30C) This is on a hay rack triaxle log trailer.

I've cleaned around the leveling valve, and cleaned around the bottom of airbags. Could this be caused by a stiff or seizing up suspension? Once up to pressure, about 70 psi, the air pressure reading stays consistent. The last 10 psi comes up very slowly.

There is also a digital readout in the cab and this takes the same amount of time to reach actual loaded weight.
Drain all wet and dry air tanks.
 

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Discussion Starter #15
Found an air leak on the line (a fitting) coming back from the trailer to feed the digital scale in the tractor. Hopefully this fixes the problem. The tare weight on the trailer is also much more stable now. See what happens on the next load!

Weather is finally starting to warm up a bit. Probably be waiting till Monday.
 

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You may have found the problem right there, I know it doesn't even take that much of an audible leak to reduce the trailer pressure to critical levels even if the truck air pressure reads fairly high and fools one into assuming the trailer tank pressure should be high as well. I had that happen where one of the spring brake pots on a trailer was starting to fail/leak and I didn't think it sounded like that much air was being lost but it was enough and that some of the other spring brakes started to apply ever so slightly.
 
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