Why is preventive maintenance necessary?

Since your HVAC system can account for up to 50% of your energy usage, it pays to improve its efficiency.  Regularly scheduled preventive maintenance properly performed, in addition to lowering overall annual HVAC service costs, and reducing the number of emergency calls due to catastrophic failures, will also result in lower utility costs. Properly maintained equipment operates more efficiently.

Preventive Maintenance is essential to the proper functioning of HVAC equipment. If preventive maintenance is not performed regularly, or if it is done haphazardly, the equipment will require extensive and costly repairs at a later date. This is not just a case of "pay me now or pay me later." It is a case of "pay me now or pay me considerably more later," and loses reliability in the process. The following will explain the specific cause and affect between neglected maintenance tasks, the failures that result, and why preventive maintenance is necessary.

Preventive maintenance of HVAC equipment, of the types typically installed in retail stores, consists of several regular inspections each year. During these inspections, proper operation of the equipment is checked and verified, air filters are replaced, drive belts are inspected and replaced as required, bearings are lubricated, and heat transfer surfaces are cleaned. In addition, if the unit utilizes combustion of fossil fuels for heating, the burners will be serviced and cleaned during at least one inspection. All mechanical equipment is designed to operate within certain limits. A passenger car, for example is designed to carry the weight of four occupants plus luggage, perhaps 1200 pounds. If you were to load that vehicle with 5000 pounds of weight, catastrophic damage would result. Similarly, if you operated a personal computer in a closed box for a length of time, it would burn up. The damage in both cases is a direct result of the equipment being required to operate under conditions that are far beyond the operating limits set by its designer and builder. Similarly, HVAC equipment also has certain design limits, and if not properly maintained, the equipment will exceed its design limitations with the result being catastrophic failure.

Why must we replace air filters?
Air conditioning equipment is designed to operate with a specific quantity of air passing over its indoor coil surface, typically between 300 and 400 cubic feet of air/per minute/ per ton of air conditioning. When air filters are not replaced at regular intervals, they clog and become coated with dirt. Similarly, the indoor coils get coated with dirt. This dirt blocks a portion of the air flow, which means that the amount of air passing through the unit drops below the 300 cubic feet of air/ per ton design limit, which can lead to catastrophic failures.

In the cooling mode, if there is not enough air over the indoor coil, the coil temperature drops. When the coil temperature drops below the freezing point, ice forms on the coil, which further reduces the airflow, which further reduces the coil temperature. The compressor within the unit is a pump, which is designed to pump a vapor. As the airflow through the indoor coil drops, there isn't enough heat being removed from the air passing over the coil to vaporize the liquid refrigerant inside the tubes, which make up the coil. Therefore, instead of receiving a vapor, the compressor receives liquid refrigerant. This is commonly known as "liquid slugging". The effect of "liquid slugging" is similar to the effect of pouring a liquid into the cylinders of an operating automobile engine. Because liquids are not compressible, the pressure within the cylinders exceeds the design limit of the cylinder, and the valves, connecting rods, pistons, or other internal components are destroyed. The units start out requiring that its filters be replaced. Now it needs a new compressor.

In the heating mode, low airflow leads to overheating of the heat exchanger. This tubular steel assembly separates the air being circulated from the flame and the products of combustion. The heat exchanger is designed to operate at a temperature between 120ƒF and 200ƒF. If the operating temperature exceeds theses temperatures, the heat exchanger oxidizes quickly and its operating lifespan is reduced below the anticipated normal life-span, or the heat exchanger cracks and breaks. In either case, it makes far more sense to replace air filters regularly than to replace a heat exchanger costing thousands of dollars.

Why must we replace drive belts?
Loose or broken drive belts cause the same problems that dirty filters cause. This is due to the fact that they also cause the airflow through the equipment to be reduced below design limits. In addition, loose drive belts slip on the pulleys they are meant to drive. This wears the groove in the pulley so that when the belt is finally replaced, the new belt is ruined in a short period of time by the worn pulleys. Once again replace the $15.00 belt on a regular basis or spend $300.00 replacing pulleys.

Why must we clean condenser coils?
Equipment is designed to operate between certain outdoor temperature limits. Cooling and condensing of the refrigerant vapor is designed to occur with a particular volume of air flowing through the condenser at a maximum outdoor ambient temperature. (Usually 115ƒF) If the finned surfaces of the outdoor coils are fouled with dirt, the ability of these coils to transfer heat is reduced and the airflow through the condenser coil is reduced. When the ability to transfer heat is reduced, the operating temperatures and pressures of the unit increase. If the unit's ability to dissipate heat is reduced, a unit, which may have been designed to operate at ambient temperatures of 115ƒF or more, may stop operating at an outdoor temperature of 90ƒF. Due to the reduced heat transfer capability, the operating temperatures and pressures within the unit exceed the manufacturer's safe limit and the unit shuts down. If the unit does not exceed the manufacturer's limits by enough to require a shut down, it will continue to run at reduced capacity and efficiency, and at an increased rate of wear due to the increased work load.

Why Inspect Relays and Contactors?
Electrical relays are designed to open and close a predetermined number of times with a particular current load, before the contact points are damaged to the degree that the relay requires replacement. If more than the design current is passed through this relay due to a motor working too hard, or low voltage conditions, the contact points overheat and become damaged. If the electrical contacts in a contactor (large relay) begin to get pitted, and the contactor is not replaced, eventually the compressor motor or the fan motor controlled by the contactor will continue to run until it burns up and require replacement. Once again, if we exceed the design limitations of the device, or its anticipated life span, additional damage is caused.

Why Must We Lubricate Bearings and Rotating Components?
Bearings and other rotating parts are designed to have a useful life span of hundreds of thousands of hours. However, this projected useful life span is based upon the assumption that the bearings will be lubricated at appropriate intervals and that the bearing surfaces will not be overloaded due to vibration from defective drive belts or dirty blower wheels. If bearings are not lubricated regularly, they will overheat and seize. When this occurs, the bearings fall apart, and the blower wheel, shaft, and housing are destroyed. This is a prime example of a situation where inexpensive maintenance was neglected with catastrophic results.

Why Must We Check the Refrigerant Charge on a Regular Basis?
Sufficiency of refrigerant charge must be checked on a regular basis. A unit operating with an insufficient refrigerant charge can ruin its compressor via two scenarios. The unit icing up due to a low-pressure condition causes the first type of failure, causing the compressor to fail due to liquid slugging, as described before. The second type of failure is due to the fact that the compressor requires a certain quantity of cool refrigerant vapor to cool its motor windings. If the refrigerant charge is not sufficient, the motor within the compressor will overheat and burn up.

The scenarios described all cause damage to occur slowly, over a period of time, usually without being noticed by the occupants of the conditioned space until catastrophic failure has occurred. Compressors and indoor blower motors should last for 10-15 years if their design limitations are not exceeded due to poor maintenance or failure of another component. Without proper maintenance, a typical rooftop unit can ruin its compressor within 1.5 years.
Regularly scheduled preventive maintenance properly performed, in addition to lowering overall annual HVAC service costs, and reducing the number of emergency calls due to catastrophic failures, will also result in lower utility costs. Properly maintained equipment operates more efficiently.