The Dog Days of Summer: 5 Common A/C Compressor Failures & Causes for Your Big Rig

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Learn the 5 most common causes of A/C compressor failures for heavy duty trucks.
Heavy Duty AC

Having a nice A/C compressor keeping you and the cab of your rig cool is the difference between comfort and being miserable in the cab of your big rig. With those hot summer days fast approaching, your A/C compressor is a key component in your overall cab air conditioning system. As a key component, A/C compressors control the operation of several other pieces in your heavy duty A/C system. When your compressor fails, the cab cooling system will not function, and you’re pushed into a scurry to not only beat the heat but also get back on the road.

In this article, we will discuss 5 of the most common causes of A/C compressor failures and the causes of these compressor failures in your heavy duty truck.

  1. 5 Common A/C Compressor Failures & Causes In Your Heavy Duty Truck
  2. Wheelco’s A/C Compressor Recommendation

5 Common A/C Compressor Failures & Causes In Your Heavy Duty Truck

  • Loss or Lack of Lubrication
  • Excessive A/C System Pressure
  • Broken or Deformed Reed Valve
  • Leaking Compressor Shaft Seal
  • Blown Head Gasket

Loss or Lack of Lubrication

A/C compressors need oil to lubricate the A/C system and the only way a compressor can supply the oil to the system is by carrying it through the refrigerant. This can be best compared to the effects of a human heart. While the human heart pumps blood through the body to provide essential nutrients, an A/C compressor does something fairly similar by pumping refrigerant and oil throughout the system. Just as a human heart will continue to pump blood until it fails, an A/C compressor will also continue to pump solvent until it binds, lockups, and eventually fails. If there is a loss of refrigerant, or a lack of refrigerant, the compressor will attempt to continue pumping what is left in the system until failure.

A/C compressors see the highest rate of failure because of the loss of refrigerant and lubrication throughout the system.

Another way that compressors see a lack of lubrication is from new compressors being shipped dry. When compressors are shipped dry, you will need to add the recommended amount of oil to the compressor. That means you, as the installer, need to determine the correct amount and type of oil to be added to the compressor. Most commonly, A/C compressors will use either mineral or synthetic oils. If you lack lubrication or use the wrong type of oil, the compressor could become damaged. Check your manufacturer specifications before installing to ensure you are using the correct amount and type of oil for your compressor.

Excessive A/C System Pressure

Too much pressure in your A/C system is destined for compressor failure. Continuing to compare an A/C compressor to that of the human heart, high blood pressure will cause the heart to overwork and fail prematurely. This is the same concept for A/C compressors as they can become overworked and begin to seize with too much pressure. The compressor will attempt to continue working but it will fail and give out over time, and you don’t want that while on the road. Excessive A/C system pressure can be caused by multiple different variables such as the following.

  • Too Much Oil
  • Inadequate Air Flow
  • A/C System Blockage
  • Refrigerant Cross-Contamination

Too Much Oil

Excessive pressure in the A/C system can also be caused by too much oil. Just as the lack of lubrication will damage your compressor, too much lubrication will do the same. Your compressor can become sluggish and begin slipping of the clutch if there is too much oil. This causes poor performance and an increase in system discharge pressure because the excessive oil will accumulate in the A/C condenser.

Inadequate Air Flow

Accumulation of oil in the A/C condenser can also cause high discharge pressure due to inadequate airflow across the condenser. Excess oil built up is not the only cause of inadequate airflow through the A/C system though. Any foreign material, such as dirt or bugs, can cause airflow to be reduced and increase the high side pressure. More commonly, faulty radiators, condenser fans, shutter systems, and fan clutches could all be suspects to creating higher pressure in your A/C system.

Heavy Duty Truck on Road

A/C System Blockage

Blockages of the A/C system are another cause of high-pressure failure of the A/C system. You can easily tell if you have a blockage by an immediate temperature, or pressure, drop just after clutch slipping. You must remember that a drop in pressure will mean a drop in temperature and vice versa. Using an infrared pyrometer, you should check the inlet and outlet temperatures of the condenser for a difference of over 35 degrees. A difference of over 35 degrees means you have a blockage problem in the A/C system. This blockage could be caused by a heavy load of contaminates reaching the condenser, which usually happens after a compressor failure. A complete system flush is usually required when a blockage occurs. However, newer designs of condensers feature two parallel passages, offering a dual-pass flow, so a blockage could still exist in one of the passages, even after a complete system flush. When doing a system flush, the solvent will take the path of least resistance. With older style condensers with one passage, the system flush will push contaminates out, while a newer style condenser will bypass the blockage by taking the unblocked path. Many newer style condensers will need to be completely replaced to remove the blockage before it contaminates other components of the A/C system.

Heavy Duty AC Compressor

Refrigerant Cross-Contamination

Different types of refrigerant used in the system is also problematic. If your blood type is A+ and you have a blood transfusion with B-, you are not going to have a positive outcome for results. That is the same concept with the use of different refrigerant types. Between R12 and R134a refrigerant, you want to make sure no cross-contamination occurs. If cross-contamination does happen, a reduction in A/C performance will occur with an increase in the high side pressure. Not to mention that your warranty is usually limited to the correct type of refrigerant and oil being used. Your warranty may be void on all A/C system components just by using the wrong refrigerant or oil. Make sure to properly flush and drain your A/C system at the time of retrofit to prevent premature compressor failure and voided warranties.

134a AC Systems

Broken or Deformed Reed Valve

Finding a broken or deformed reed valve is not uncommon. Symptoms that point to a reed valve issue are usually a lack of cooling with unusually high suction pressure of the low side and unusually low discharge pressure of the high side. You may think that your compressor is not pumping but in reality, it is; there is just an issue with your reed valve. Before making any assumptions though, you should always check that there’s not a low refrigerant charge. If you’re able to confirm that your refrigerant is at a proper charge, the next step is to listen for any unordinary noise at idle. Because of the excessive moisture in the system, reed valves can easily become corroded and break off. Most broken reed valves can be heard making a clicking sound while your rig is idling. If your refrigerant charge is at proper levels and you hear no sound, then a damaged or deformed reed valve is most likely the cause.

Leaking Compressor Shaft Seal

Another compressor failure that can be attributed to a system problem is a failed compressor shaft seal. An excessive amount of heat or pressure in the system can cause a shaft seal to fail and leak. When a seal leaks, the compressor oil can find its way into the clutch bearing, contaminating the bearing grease and leading to grease seeping out of the bearing seal. Shaft seals are extremely important to the protection of your heavy-duty equipment. If you’re working in an environment with high dust and dirt content, the shaft seal could see a shortened lifespan. Newer seal designs and technology have improved significantly to help reduce seal issues, but your due diligence can help protect the compressor shaft seal for years to come. To help avoid premature compressor shaft seal leaks, follow your manufacturer recommendations and always turn your compressor clutch by hand to check for any leaks before starting the compressor into operation.

Blown Head Gasket

Blown head gaskets are usually found by a lack of cooling with unusually high suction of the low side, with an unusually low discharge of the high side while idling. If you believe you may have a blown compressor head gasket, run your system for 5 minutes at idle and shut it off. Watch the time it takes for both pressures to equalize. Less than 2 minutes on a TXV system and your gasket may be damaged or blown. CCOT systems will equalize even quicker than the 2 minutes if there is a damaged or blown gasket present. Blown compressor head gaskets are usually the result of excessive head pressure.

Wheelco’s A/C Compressor Recommendation

At Wheelco, we pride ourselves on being customer driven and providing the best solutions for you. MEI Corporation is the brand we trust to keep your A/C system running cool during those scorching hot summer days. With A/C components for all makes and models, MEI has grown to become the largest independent provider or heavy-duty air conditioning and heating components in the United States.

Specializing in HVAC products for Class 6, 7 and 8 trucks and forestry, mining and agricultural equipment, MEI Corporation is the industry pioneer in the distribution of air conditioning and heating components for heavy-duty equipment. Through AirSource and Truck Air Parts, MEI offers the industry’s only “True All Makes” air conditioning and heating parts that include, compressors, condensers, receiver driers, expansion valves, blowers, switches, and more!

It’s a tough road out there and we want to make it comfortable. That’s why we have Wheelco experts ready to answer your heavy-duty air conditioning questions and needs. Stop by any of our Wheelco locations or give us a call and see how we can help you stay cool.

About Wheelco Truck & Trailer

At Wheelcobeing customer driven is more than just a motto we live by. It means that our employees will do everything we can to best serve you, our valued customer.

Customer driven is more than just offering you advice, giving time-honored service or contributing the latest tech-support. It’s about being there—whenever and wherever you need us—in-person, over the phone or online.

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