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Old 07-12-2009, 11:15 AM   #1
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Question Is this the way your chassis air compressor works?

Greetings Everyone! This is my first post on this forum.

We now have our first rig with air brakes/suspension and air compressor. My first use of the air compressor tested me for a few minutes. At first I had trouble getting the air pressure up enough to fill the tires. I finally made sense of the way it was working, but not having on board air previously I don't know if it's operating correctly. I will explain what I observed and would appreciate comments on whether this is the way your air compressor works.
  • The only time I get high pressure from the air outlet is when the compressor is actively filling the air tanks. Once the air tanks are full I only get a nominal low pressure pulse from the outlet.
  • The maximum pressure I get is the tank pressure. This makes sense.
The combination of these two characteristics means I have to constantly dump air via the brake or dump switch, but not too much air so there is enough pressure to fill the tires. This seems like more trouble than it should be. If this is normal I can work around it. If I have to inquire to Freightliner I would like to have some background from others with experience to have some credibility with the inquiry.


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Old 07-12-2009, 05:31 PM   #2
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Rather than go through all of the same things that you are doing, I purchased a 150# air compressor off of the internet and carry it with me. So far I have not had to use it other than at the beginning of a trip when I equalize all of the tires.

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Old 07-12-2009, 06:11 PM   #3
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Greg 09,
You are a fast learner. What you have observed is how it works . I put a air pressure gage on my line to watch the pressure. When i hear the air valve spit, I have wife hit the brakes to lower pressure to 95 and then watch the gauge for it to start climb and add air to tire.
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Old 07-12-2009, 06:14 PM   #4
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Mine works the same way. I need 110 pounds for the tires and the pressure where the compressor kicks in is less than that.
2010 Winnebago Tour 42AD, Cummins ISL 400, Allison 3000, Progressive EMS, Aventa II, Air Force One, Tire Safeguard TPMS, Blue Ox Tru Center (maybe), Lotsa LEDs
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Old 07-12-2009, 06:20 PM   #5
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First let me welcome you to IRV2 Gregg.
From my own experience I have found the compressor has a high limit and a low limit. My high is 135psi and low is about 100psi. In trying to fill a tire to say 110 psi the compressor will cycle on/off. When it reaches the max the tire will fill, when the pressure drops below the 100 psi it will again cycle on and since it is below the pressure you want it is ineffective. Just let the compressor come back to a "filling" pressure and you will be ok.
Another thing you have to remember is it takes time to fill a tire to 110/120 psi. It's not like filling a 19.5" tire.
I'm sure you will get a better answer to your question, knowing this group, but at least we got it started.
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Old 07-12-2009, 07:03 PM   #6
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Try using high idle and see if that helps. What you are doing is the way we do it.
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Old 07-12-2009, 08:15 PM   #7
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Thanks for the quick responses. Since the compressor works like everyone elses there's no worry. I can use my portable air compressor at home before a trip but won't need to drag it along. Using the chassis air compressor will be fine when on the road.
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Old 07-12-2009, 09:04 PM   #8
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have U weighed and checked?

My question is:

First) Have you weighed your coach to get the axle (or individual corner) weights?

Second) Have you used the tables provided by Michelon, Goodyear, etc to determine the proper inflation pressure of your tires based on the weights?

After doing this I found that I had been over-inflating my tires by at least 10 pounds.

My tires are all inflated to less than 100 pounds ... the ride and handling improved greatly ... I recently replaced my tires because the DOT stamp was more than 7 years old ... they had 69,000 miles on them.
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Old 07-12-2009, 09:24 PM   #9
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I bought something at Harbor Freight called an inline air-blow gun, part number 96792-Y, that lets me release enough pressure to start the compressor while filling tires. My air hose feeds one end, and my chuck comes out the other end. Very easy fix. Good luck, HarveyP
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Old 07-14-2009, 08:15 AM   #10
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I am in the minority so maybe my compressor is regulated wrong. I have only checked my pressure with dash gauges which always read about 130 psi when the engine is running. I do get occasional releases of air from the pressure release valve. Now I am wondering about my compressor operation.
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Old 07-14-2009, 09:38 AM   #11
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Originally Posted by skigramp View Post
My question is:

First) Have you weighed your coach to get the axle (or individual corner) weights?

Second) Have you used the tables provided by Michelon, Goodyear, etc to determine the proper inflation pressure of your tires based on the weights?

After doing this I found that I had been over-inflating my tires by at least 10 pounds.

i must agree, after the arrival of my first lil bus up from fivers i to tried to max out the air pressure and was up against a wall getting enough pressure, i was used to running my fiver tires at max pressure because i was heavvvvvy.
these folks here kindly poked my mind a bit and i was re-trained
i run 103 up front and 95 out back, these pressures were from weighing and road feel and tire contact patch, i used my shiny concrete pad as a test bed for tread contact and compared it the Goodyear picture, at these pictures and my current load i get great contact and good ride-ability.

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Old 10-30-2009, 05:46 PM   #12
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I don't currently have MH with air brakes yet, (shopping), But I did service trucks for many years. If your compressor has to be cycling, Your air tap is in the wrong place in the circuit.

The basic circuit runs from the compressor to the air dryer and nothing should be tapped into that part of the circuit. When you hear the spit valve on the bottom of the air dryer, that part of the circuit, air compressor and dryer, are reduced to ambient pressure and the compressor is just free-wheeling. there is a check valve either in the dryer or just before the wet tank.

Taps should only be plumbed into the secondary air circuit. Reason being, if the tap should fail, you should only lose the secondary tank. The primary tank should keep the parking brakes from suddenly locking on untill that drops to around 40- 60#. In a crunch, this will give you 2-3 brake applications of the rear brakes allowing you to safely stop.

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