[Skip to Content]
Time is Money. Find out more about how this app can revolutionize the way you weight your truck.

Avoiding Air Compressor Problems

By on November 1, 2019

Worried About Shutdowns? Stop Old Man Winter Cold!

By: Homer Hogg, Director, technical service

As if subzero cold, blizzards and slippery driving conditions aren’t punishment enough, Old Man Winter is eager to teach you a lesson about a lack of seasonal preparedness. When it comes to making sure your truck’s air compressor is up to the task, you can simply avoid problems by taking preventive measures before winter’s worst shuts your rig down.

When it freezes, excess moisture in your air brake system is virtually guaranteed to wreak havoc. Even though that’s a simple concept to understand, we still see many truck owners—particularly owner-operators and small fleets—that just don’t find the time or flat out forget. The first rule of preventive maintenance is simply draining your air tanks and servicing the filter in your air dryer. Checking the condition of the moisture as it exits the air tank and settles on the ground is also very important.

Oil, Rust, Excess Moisture

You must check for three major enemies: oil, rust and/or excessive moisture. The presence of oil indicates it’s passing through your air compressor. Rust indicates the inside of your air tank is deteriorating, which could ultimately lead to a very serious problem requiring tank replacement. Excessive moisture usually indicates that your air dryer is malfunctioning.

If oil is present in your air tank or tanks, you can apply a process of elimination to check your air compressor. First, check to be certain your air compressor is pulling in enough clean air. The air comes from the clean side of the air filter. If your air filter is restricted, your compressor will try to draw air from the compressor’s oil sump, which will result in oil entering the air brake system. In some cases, the intake line or port to the air compressor can be restricted by contamination, which will cause the same problem. Some trucks have a mesh filter at the compressor inlet to help ensure that clean air is reaching the compressor. In this case, be sure to check this filter and replace or clean it accordingly.

Once you’ve eliminated the possibility that the air compressor intake is restricted, but oil is still passing through the compressor, it’s time to replace the compressor. Another place that confirms your compressor is passing oil is the bottom or exhaust of the air dryer. If oil comes out of the dryer when you hear the air exhaust, that provides a good indication that oil is passing from the compressor to the dryer, then on to your air tanks.

Compressor Performance Issues

Next, you want to be sure your air compressor is performing as the manufacturer intended. Conduct a pressure buildup test. If your brake system is standard—meaning it does not have air tanks added for additional axles or systems—the air pressure must build from 85 psi to 100 psi within 45 seconds when the engine is operating at the manufacturer’s maximum rated rpm.

Slow buildup time can result from an excessively worn compressor, restricted compressor intake or discharge system, or in some cases, the compressor is simply too small or unable to produce enough air volume for the truck. This can happen when a compressor has been replaced with one that is too small for the application, or if additional axles or air components have been added. Frequent air compressor replacements provide a good indication that the compressor is working harder than intended. As always in maintenance matters, the root cause of any compressor problem must be determined and corrected.

Slow air pressure buildup time or the pressure not building at all is one of the most challenging diagnoses to make. The air governor is responsible for maintaining your truck’s minimum and maximum air pressures. A small air line or air port connects the compressor to the governor. This allows air to flow from the governor when the compressor has delivered enough air to the air system. The governor monitors the air pressure in the air tank and allows some of the air to flow to the air compressor once the desired pressure is achieved.

If the governor does not shut off the airflow to the compressor, the compressor will not build air. Simply remove the small air line from the air compressor and see if the truck will start building air. If it does, then the problem is with the air governor, not the air compressor. If air is going from the governor to the compressor and the intake or discharge lines of the compressor are not restricted, the compressor is at fault and must undergo additional evaluation. Unloader rebuild or compressor replacement will likely be required.

Discharge Line Caution

An additional challenge TA Truck Service technicians see when air compressors don’t build air properly is a restriction in the discharge line. This is the large-diameter line coming from the head of the air compressor. Be very careful around this line because it can be extremely hot and can cause severe burns if you touch it with your hands. Carbon can build up inside this line, keeping air from building in the air system or can cause some unusual problems such as a leaking air dryer.

With the bitter cold Old Man Winter is capable of delivering in the coming months, now is a great time to make sure your air compressor is up to the challenge. Keeping your braking system fully supplied with specified air is priority one. You’ll also want auxiliary systems such as your air-ride suspension and air-ride seat to keep you comfortable as you move your freight on down the road. If you need assistance diagnosing and repairing air system performance problems, TA Truck Service technicians are ready to put their extensive experience to work for you. 

About Warren Eulgen

Leave a Reply

Your email address will not be published. Required fields are marked *