Tag Archives: HVAC

Lubrication and Compressor Life

A wise engineer once told me that “lubrication is the secret to life” and that is certainly the case when it comes to AC system compressors.  Design and development engineers strive to find the proper balance between adequate oil charge to lubricate the internals of a compressor and having too much oil in the system.   Too much oil will degrade AC system performance by inhibiting heat transfer in the condenser and evaporator.   Overcharging a system with oil can also cause problems with variable displacement compressors that use mechanical control valves.   When it comes to oil in an AC system more is not better.

My colleague, Richard Hawkins, from the 1-800-Radiator & A/C technical support group reviewed the topic of “A/C System Lubrication System Issues & Concerns” at the 2020 MACS Conference in Nashville, TN.   Some lubrication and service issues are summarized in these slides from his presentation at the conference.

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MACS members can find Richard’s entire presentation at:




Condenser Contamination

We all understand that condenser performance is affected when air flow is restricted by dirt, grass, salt, and other contaminants plugging the air side of the condenser.   Debris plugging the air side of a condenser causes the system to operate at higher pressures and temperatures which can affect not only comfort but can lead to premature compressor failure.  On the other hand, it is just as important that the refrigerant side of a condenser remains clean and unobstructed if optimal performance and reliability is to be achieved.

When a compressor fails the debris from the compressor as well as the contaminated oil must be cleaned out of the condenser and other components to assure a trouble free – reliable repair.  Because the refrigerant side of newer condenser types cannot be cleaned effectively they must often be replaced as part of the A/C system repair.

Most automobiles on the road today use R134a as the refrigerant in their A/C system.  When R134a was introduced as a replacement for R12, higher capacity – more efficient condensers were needed to compensate for the differences in the thermodynamic properties of the new refrigerant.  Since the space available for the condenser is limited by the layout of the engine cooling compartment, engineers had to find ways to increase capacity without increasing the overall size of the condensers.  

The requirement for increased heat transfer capacity led to application of new styles of condensers to replace the conventional tube and fin and serpentine designs that were being used by the vehicle manufacturers.  The photo below shows cross sections of four types of condensers starting with a conventional tube and fin design on the left, followed by another tube and fin variation, then a serpentine tube design, and finally a parallel flow condenser.  These cross sections illustrate how individual refrigerant flow passage size has become progressively smaller with each evolution of condenser designs. 


                  Tube&Fin      6mm Tube&Fin   Serpentine     Parallel Flow

The early generations of parallel flow condensers have now been superseded by new designs with even smaller refrigerant flow passages.  A tube from one of the most advanced designs is illustrated in the photo below.


Micro – port condenser tube

The tiny flow passages in a micro – port tube can be obstructed even more easily by contamination from a worn or failed compressor.  Some passes in the condenser have as few as three of these tubes arranged in a parallel layout between the opposite ends of the condensers.  If one of these tubes becomes obstructed the overall capacity of the condenser is degraded and oil circulation vital to compressor life is compromised.

Condenser evolution did not stop with the introduction of the parallel flow condenser.  The desire to reduce refrigerant charge volume, while further reducing the space and mass requirements of the A/C system, prompted the development of condensers with integrated receiver – driers and sub-cooling sections.  In this arrangement a section of the condenser is reserved for sub-cooling the liquid refrigerant as it exits the receiver-drier.  We will provide more details about the function and benefit of the “sub-cool” type condenser in our next tech tip.

Meanwhile, the key point to remember is that all parallel flow condensers trap material and contaminated oil that is discharged from a failed compressor.  When this contamination blocks the small flow passages in the condenser, cooling capacity is reduced leading to higher system temperatures and pressures.  Severe cases of contamination will obstruct oil flow thus preventing proper lubrication of the compressor.  If there is reason to believe the parallel flow condenser may be contaminated it should be replaced whenever a new compressor is installed.  In some applications both the OE and aftermarket service protocols require condenser replacement to validate new compressor warranties.

Introduction to the Iceman Cooling Journal

The purpose of this blog is to share tech tips with automotive service professionals and do-it-yourselfers who maintain engine cooling and climate control systems in cars and light trucks.