Air conditioning equipment
© seraficus

How to make sure your air conditioning keeps its cool

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    If you’re going to have an air conditioning failure, it’s going to occur during early summer; when most air conditioning breakdowns materialise

    That’s why we’re offering tips from our  engineers on how to avoid the most  common air conditioning   problems  with a little strategic maintenance.

    The section numbering of this guide directly relate to the  references shown on the three diagrams.

    Hermetic air-cooled reciprocating system (25 HP)
    Typical 300 ton centrifugal system
    Open water-cooled reciprocating system (25 HP)
    • Check air ventilation openings on  open-type motors for obstruction.
    • Check bearings on open-type motors  for adequate and proper lubrication.
    • Have insulation resistance meter  readings taken on motor windings.  If resistance is less than one megohm, don’t start the motor. (For hermetic  motors, be sure the crank case heater  is energised at least eight hours  before this test.)
    • Remove the covers on the motor’s  magnetic starters and examine  the contacts. Compressor cycling  can make them deteriorate. Look  for pitting or corrosion.
    • Check all terminal connections for tightness.
    • Check the overload protection  for defects and proper sizing.
    • Make sure timing devices have the  correct operating sequence.
    • Check mechanical linkage for binding  and looseness.
    • Check fans for broken, cracked, bent  or loose blades and hubs.  
    • Check the fan shaft and bearings.  
    • Check belt tension and condition.
    • Check it for proper superheat setting  over its full range of operation. If it's  not operating within its design limits,  it can affect the safe operation of the  equipment.
    • They're the heart of your equipment. Make sure they're properly calibrated and in working order.
    • Immerse thermal sensing controls in a cold medium to verify the condition and setting of their sensing elements.
    • Test oil pressure differential switches mechanically and electrically. Flow switches should be removed from the  well for examination. Be sure to look for signs of corrosion on the paddle and linkage.
    • Check the condition of pump  bearings, packings, shaft couplings  and seals.
    • Clean air-cooled condensers, but  only with a solution marketed for this  specific use. Take care to protect the  fan motors from any moisture.  
    • Remove the heads on shell and tube  condensers and clean the tubes of  scale and debris.
    • Clean the coils, sump, spray nozzles  and overflow drain on evaporative  condensers.
    • For cooling towers, clean the sump  and spray nozzles and check the  baffles for tightness and soundness.
    • Check the makeup water valve to be  sure it’s operating properly.
    • At least eight hours before start-up,  hermetic compressors need to have  their crank case heater energised.
    • This step is vital: preferably, leave the  heaters energised for the rest of the  season; when the compressor is idle,  the heater will prevent refrigerant  from migrating to the compressor.
    • Have the cylinder heads removed  and check the compressor valves at  least once every two years, or every  10,000 hours. Valve failure is one of  the biggest causes of compressor  breakdown. If you see signs of wear  or fatigue, replace them (valves are  relatively inexpensive).
    Avoid lubrication failure

    Lubrication failure is one of the biggest causes of equipment breakdown. Without proper lubrication at all times, moving parts in the motor-compressor  wear out, overheat, burn and break.

    Every year, have your service  technician check the oil to make sure  it’s suitable; clean and non-acid.

    Also have the technician leak test the  system regularly, and repair any point  of leakage immediately.  

    When the system is idle, look through  the oil sight glass to check lubrication  in the compressor crankcase. The oil  level should remain constant. If you  temporarily lose oil in the sight glass,  you may have unwanted refrigerant in  the crankcase. Call  the service  technician at once.

    Oil and refrigerant leaks often show up  as oil spots with dust accumulations –  a symptom of trouble.

    Check these likely leak spots every  week: compressor shaft seals •  piping joints • coils • vessels •  compressors • motors.

    Moisture hurts any refrigeration  system; preventing proper lubrication,  corroding or copper plating the moving  parts, and freezing in the expansion  valves. The result: erratic performance,  inefficiency, and even breakdown.

    Moisture can enter the system if  water-cooled condensers or water  chillers leak. It can get in accidentally  when you’re charging refrigerant or oil  into the system, unless you take  special care. Here’s how to check for  moisture problems:

    • Equip your refrigerant circuit (liquid  line) with a moisture sight glass  indicator. Look for any change in the  indicator chemical colour. If the  colour changes toward ‘wet’, make  sure your service technician corrects  the problem, cleans and dries the  system, and installs proper liquid and  suction line filters and dryers.
    • It’s even more important to  determine the source of the moisture  and to correct it right away. You may  need to leak test any water-cooled  condensers or chillers.
    • Normally, you’ll see a pattern of clear  liquid flow. If you notice other  changes in the flow pattern (such as  gas bubbles in the liquid refrigerant),  have the system checked to see if it’s  properly charged with refrigerant.  Control malfunction can also cause  flow pattern changes.

    Effective air conditioning depends on reliable temperature and pressure controls. Each is calibrated to perform a specific function. Periodically, have them serviced, adjusted and prooftested; and only by qualified personnel.

    When your system shuts down, check these areas

    Above-normal room temperatures invariably spell trouble. If there hasn’t been a power interruption and all other checkpoints appear normal, call the service technician.

    If the motor-compressor has shut down, don’t attempt to restart the system

    Protective controls may have tripped it off; find and correct the cause of the trip-off. Don’t attempt to restart the system – it could result in severe equipment breakdown.

    Don’t attempt to adjust regulating  or protective controls yourself

    This is the time for an expert to  diagnose and correct the problem.

    Avoid pressure problems

    Try to determine normal discharge and suction pressures (your air conditioning unit may be equipped with pressure gauges). As with temperature changes, any increase in pressure is reason enough to call the service technician at once.

    Dirty condensers are a key cause of pressure and temperature problems. Make sure the technician verifies that the condenser is clean. If you have a water-cooled or evaporate condenser, use an effective water treatment to prevent scale, corrosion and algae.

    • Keep air filters free of dust particles,  smoke and dirt. Keep a careful log of  cleaning dates to maintain an effective  cleaning schedule.

    Absorption unit systems1

    Evaluate the lithium bromide solution  concentration and the lithium bromide  inhibitor.

    Check the absorption purge unit and  purge system for proper operation.  

    Examine all canned motor pumps  used on the absorber unit and check  the bearings for wear. Look carefully  at the condition of the motor stator  and rotor seals.

    Our diagrams can help you work  with service people to identify parts  needing replacement, points of  refrigerant leakage, with regulating  and protective control settings, and  other critical features.


    Insulation should be checked for breakdown of the vapour barrier. This could be due to external damage or the insulation deteriorating. The failure of the insulation is usually indicated by condensation or frosting on the surface. In such cases, the insulation should be remove and the pipework inspected for any surface corrosion and be protected as necessary, prior to reinsulating.

    If operating characteristics change,  watch out

    Each system has its own normal pattern of noise, vibration, speed,  temperature and pressure. They can  vary depending on the season and the  heat load your system handles. Once  you've familiarised yourself with these  normal conditions, you’ll be able to  spot trouble signs.

    Any change in normal operating  characteristics is a warning. Call the  service technician if you notice:

    • an unusual noise or vibration
    • a strange odour
    • oil or water spots
    • sudden changes in temperature, speed or pressure.

    Correct the problem at once.

    Suspect a problem? Call your service firm.

    That’s critical advice. Consult  with a professional before  undertaking any maintenance  steps or repairs. An adequate  service programme may cost  a little more up front, but it will  pay off in long-term savings.

    Our advice is intended to complement the equipment manufacturers' recommendation – not replace them.  If you have doubts about any particular procedure, call an air conditioning service firm.

    1. Absorption unit system diagram not shown  in this document

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