Why Is My Truck Not Building Air Pressure? Find Out the Main Causes Here!

Ever found yourself in a situation in which your semi-truck built pressure just fine a moment ago, but after turning it off, it bled off? When having a truck not building  air pressure, it’s natural for truckers to start worrying. That’s why today we’ll show you the main reasons why this problem happens and what you can do to fix it.

How Long Should It Take to Build Air Pressure on a Truck ?

First, you must be aware of how your air brake system works. And, among the essential things truckers must know regarding these systems, we have the usual time a truck should build a safe amount of pressure.

An air brake system works by using compressed air rather than hydraulic fluid. This compressed air comes from what we know as an engine-mounted compressor. This component then pumps the air through the air lines  onto the storage air tanks, which keeps it there until the truck will need it.

As a result, you’ll count on enough air for the emergency brakes.

Additionally, another thing to keep in mind is the discharge lines, which help the air, oil-vapor, and water-vapor mixtures to cool off between the compressor and the air dryer.

So that brings us to our main question: how long should it take for your semi-truck to build air pressure? On average, air compressors tend to take 45 seconds or less to have pressure buildup between 80 and 135 PSI (pounds per square inch).

However, since every vehicle is different, know the normal air pressure for your truck.

What Causes a Truck Not Building Pressure?

When having a truck not building air pressure, it is usually because the unloader valve is stuck. However, if there’s a lot of pressure , and it still doesn’t kick the compressor, it means that you have a faulty air governor.

Moreover, be sure to check for air leaks and your truck’s emergency and service lines, as these things can also cause this problem to arise.

How to Check on Your Truck’s Unloader Valve

Unloader valves are vital for air brake systems because they release any trapped air inside the tank. By doing this function, the motor can restart after each cycle.

Believe it or not, unloader valve issues are much more common than you might expect, especially on EGR trucks. It’s usually because these types of trucks tend to generate a lot of carbon, which then sticks onto these valves.

And, fortunately, you can temporarily fix this issue by following a few simple steps.

Opening the Hood and Finding the Unloader Valves

First, you must open your truck’s hood and locate the unloader valve. Then, you’ll want to tap on it with a hammer. That way, you’ll allow the vehicle to build enough air for your next stop.

Keep in mind that you’ll want to wait a couple of minutes to accumulate air pressure. Then, start your engine and drive to your nearest destination.

Cleaning the Unloader Valves

Once you’ve reached your stop, you should proceed with cleaning the valves. If you have a rebuild kit for your unloader valves, then feel free to place the new equipment that comes with it, such as gaskets and O-rings.

When cleaning the valves, be sure to proceed with caution. Start by unscrewing the top bolts using a 9/16 wrench of the lid. Then, remove it and take a pair of needle-nose pliers to pull the unloader valves out.

After taking them out, you’ll want to evaluate their status to ensure that there aren’t any cuts. Proceed by cleaning them using any type of carburetor cleaner or soapy water. Be sure also to use this cleaner on the valve holes to clean up the grease.

Finish off by using compressed air to clean up the holes and spray a bit of lubricant into them.

Finally, place the valves and lid again, and tighten up the bolts.

Steps on Inspecting Your Air Brake Governor

Since compressors in an air brake system work every time you have the truck running, it relies on governors to control it. Without it, the air coming out from the compressor might pose a threat to you.

For this reason, when a governor becomes faulty, it’s common for it to produce too little or too much air pressure.

Since faulty governors are dangerous, truckers must test them as part of their pre-trip inspection.  Other trucking safety tips to follow include managing their fuel economy and staying on top of the oil change interval

You must perform two types of tests on the governor. These tests are to check if the governor can put the compressor in the load and unload phase.

First, you must pump it down to above 80 psi. Then, throttle your truck a bit and notice if the needles are climbing. If they do, then you can be sure that the compressor is in the load phase.

To test if the governor can switch the compressor to unload phase, you’ll want to pump up your truck to max pressure. After reaching its highest point, the air dryer should purge, and the needles will stop climbing. One thing to note is that you shouldn’t hear the governor itself when performing this test.

The maximum pressure usually ranges from 105 to 135 PSI.

Top Red Flags That Your Truck’s Air Governor Is Bad

These are the main warning signs you should look out for a faulty air compressor:

• Both air gauges stay still for many minutes.
• You experience fast cycling from the wet tank.
• The truck builds up too much or too little pressure.
• You can hear a percussive sound coming from the safety valves.

Now that you know the main reasons behind a truck not building air pressure, you should now apply what you’ve learned in this article. Remember that you can always count on LV Road Tec Assistance LLC if you require professional semi-truck assistance on the road. We provide our services anywhere, and anytime truckers need them.