Pretty much any planned maintenance, often referred to as preventive maintenance (PM), is proactive in nature, as it helps ensure more expensive repairs are required far less frequently and keeps a system operating at optimum levels.
The key components of maintenance include how often and when (they are not necessarily the same thing), along with the payback on investment.
Before you can understand what is important in a preventive maintenance program, you must know what is important for a system to operate optimally and what causes things to fail prematurely.
To start, let’s look at what an AC/R system needs to do its job, which is to take heat from one area and move it to another to dispose of or find a good use for it.
A temperature difference must exist between the refrigerant in the heat transfer coils of the unit (evaporator and condenser) and the air or water it is taking heat from or adding to.
The compressor supplies the energy to increase the pressure and thus the temperature of the refrigerant in the condenser where the energy absorbed by the evaporator and added by the compressor is expelled from the system. The closer the refrigerant and air/water are in temperature, the less energy is required to move the heat.
This is due to the pressure difference between the evaporator and condenser being smaller so the compressor is required to do less work to increase the pressure between the two.
Let’s take an example of an AC system operating on a hot day. A lower efficiency system may require a 25F temperature difference (TD) between the refrigerant and the air to reject enough heat.
If the air is 90F, the refrigerant must be 90+25 = 115F. For R410A, this equals a pressure of 392 psig. If we were to switch to a larger condenser that only required a 15F TD, the refrigerant would only need
to be 105F for a pressure of 340 psig. This lowers the pressure difference between the evaporator and condenser so the compressor does not need to lift the pressure as high, which saves work and energy. It also means the compressor will run cooler.
Now, consider the same system but with dirt and/or other contaminates on the coil. This acts as insulation and reduces airflow, both of which require the refrigerant to be even hotter to reject the necessary heat.
Even the more efficient system will operate hotter and use more energy, possibly a lot more as you are basically taking a high-efficiency system and turning it into a low-efficiency one. Nobody would pay for a high-efficiency system and accept a low-efficiency system, but that is what they are essentially doing after the first year or two if they do not have a good PM program.
Aside from temperature difference, but tied intimately to it, is airflow. Good airflow is essential for a system to operate as intended, not only from a heat transfer standpoint but also an air delivery perspective. If you spend the money to operate the system but can’t effectively deliver the treated air to where it is needed, what is the point?
Concerning heat transfer, if there is reduced airflow through the evaporator, the TD of the refrigerant and air must increase to accommodate for it.
The result is more energy being used by the compressor to lift the pressure to the necessary level so that heat can be rejected from the condenser. There will also be less cooling to reward for the increase in energy usage, resulting in longer run times, poor dehumidification and lousy occupant comfort.
Another area of focus in a good PM program is power quality. Poor voltage and/or power factor will result in hot motors with low life expectancy and high electrical bills. In fact, utilities are penalizing customers with poor power factor by adding surcharges onto their already high bills. While the solution to some electrical issues can be more involved to correct, ascertaining electrical quality is relatively straightforward if you have the right skills and tools.
Finally, it is important to remember little things can add up to big headaches down the road. Loose terminal connections on power supplies or motors can
result in hot connections, melted insulation and failed components.
Also remember rubbing tubing, excessive vibrations, plastic bags blowing onto a coil surface, or just about any crazy thing you can dream up. It is amazing what you can find in electrical boxes, too — I have seen snakes, lizards and mice, all very toasty and all very unwelcome.
Now that we have established the “science” behind PM, how do you convince customers of its value? Especially since they may view it in the same manner as insurance policies for washer and driers that may have been foisted on them at some time? Or, even worse, they paid almost more for some insurance over time than the original price of what they were trying to protect in the first place?
The easy answer is that insurance policies only kick in if something fails and do nothing to prevent it, or make something work more efficiently and longer. While it can be said a good PM program is insurance against problems, it is not an insurance policy per se.
Since we have already established energy is required to move heat from one area to another and we have discussed the key processes required, it only makes sense to focus a PM program on ensuring these key elements occur using as little energy as possible and letting the system operate as cool as possible.
It is safe to say any system operating for 20 years with the same compressor almost certainly never operated hotter than required, had poor voltage supplied to it and had good airflow and tight electrical connections. It is possible to have a simple PM program that is also very effective.
It’s also easier to explain the benefits if the program is uncomplicated and its value directly relatable to a key operating point. Here are some points to emphasize:
In the end, good communication and patience pay off. Training for “soft skills,” such as appearance, mannerisms and building a trusting relationship goes a long way. These are all key, along with a good track record of doing the job right the first time so you build trust with your customer. Just about everyone can understand the points above if they are explained correctly.
Believe it or not, one of the best times to offer this service is after service is completed due to component failure or some other preventable reason. The customer may not be ready right then, but they will remember the pain and be more open to preventing it going forward if you can show the failure could have been avoided altogether with a good PM program.
