Tip & How-To about Heating & Cooling
Want to extend the life of your central HVAC system? Two words come to mind- Preventative Maintenance. An annual service on your equipment can be performed by a professional for a reasonable fee, usually including an annual condenser cleaning, evaporator cleaning on an as-needed basis (the frequency of this depends largely on usage and climate), drain line flush, and worn or old control electronics replacement. Changing filters on a regular schedule is the single most important task in preventative maintenance (PM).
There are many options as to which type of filter you use. Hogs hair filters are arguably the cheapest seeing as they are reusable. These have the drawback of OSOM syndrome- out of sight out of mind. As time goes on these become more dirty and catch less. I do not recommend them as they do not protect the system in the long term as well as throw away types. Fiberglass filters are the cheapest of the throw aways. These work fine if changed very regularly, but will not trap smaller particles which will over time find their way to your evaporator coil. I would never allow one of these to stay in my system for more than a month. Pleated filters round out the common filter types. Some of these can cost as much as 10x as the cheaper one- unless your system is engineered to handle extreme hepa filters do not use these. The airflow restriction causes the blower to work at an unnecessary rate and shortens the life of the motor, and can also cause coils to ice over, limit switches in gas furnaces to shut the system down, etc. The best route to go is the cheaper pleated filters, readily available in most sizes. Checking them once a month and replacing at least every 2 months has shown to be the best working solution, although extremely dusty homes may require bi-monthly changing.
The 2 components requiring regular cleaning are the evaporator and condenser coils. The outdoor section can usually be cleaned with a water hose and a good spray nozzle. This unit lives outside 24/7/365, so no, a bit of water will not hurt exposed parts while running. This should be performed annually at least, though a quick spray down every few months doesn't hurt. The idea is simply to remove dirt from the coils. While you are at it, all those leaves and such lying in the bottom of the cabinet are not helping anything but the rot of the surrounding metals. The top of most condensers consists of a fan. On these you can simply shut power down to the unit and unscrew the fan housing to get this out of the way. The compressor can be very hot, so watch out not to burn yourself while removing debris.
The other annual necessity is the condensate drain The condensate drain is the line which drains water from the AC unit to the exterior of the home, usually 3/4 PVC pipe. This can be cleared by using pressurized gas (up to 60 PSI) or, my choice, a wet/dry shopvac. Once cleared you can backflush the line from outside with a water hose. The premise is to fill the line completely with water back to the condensate pan, then let it flush itself out using gravity. In doing this one must be careful not to overfill the equipment- water will drain from the unit to whatever lies below it. This technique is something one perfects with experience. Generally 4 or so seconds of having the hose attached to the line using our hand for a seal is long enough to probe the system, incrementing in 1 second intervals each attempt. What you are looking for is gunk in the water which rushes out after you've taken the hose off of the drain pipe. Once gunk (technical term) starts to flow heavily you've figured out how long it takes for the water to reach the evaporator, 2-3 iterations at this interval are usually enough to clear a system adequately.
Cleaning an evaporator:
We've reached the end of the easy stuff- if you don't have a good degree of mechanical aptitude stop now and call a service tech every other year. The evaporator is located inside of air handlers in heat pumps, coil boxes on a ducted side of a furnace, or in mysterious locations inside of packaged units. You may easily locate split coils by following the linesets. Wherever it is, you will need access to both sides of the coils. A quick visual inspection should show a shiny aluminum surface- the luster of a soda can. Anything other than this and the coil should be cleaned. There isn't a safe household version of the chemicals an experienced technician would use, but Simple Green degreaser works well when applied liberally. A pressure sprayer is ideal, but a standard spray bottle can be made to work, though it is much more labor intensive. In cases where the buildup on the coil is minimal and the particles are all small in size a good flush with this solution is sufficient, remembering to rinse with water afterwards. Some coils have larger particles, usually pet hair, forming cakes on the surface. These need to be mechanically removed. A stiff paintbrush or toothbrush can be used to clean these off. Being careful not to bend or break the coil fins, run the surface in the direction of the fins from one side to the other (or top to bottom if you prefer). Once large particles have been removed, another flush with degreasing solution is required. After cleaning a coil, it is always a good idea to run about a gallon of water through the condensate drain to clear biological material from the line. Remember that bent and broken fins are very difficult to repair and if left cause the system to be less efficient. Also remember that the fins on these coils are quite sharp and the copper lines coming in and out of the coil can be quite fragile, so take your time and be careful. There are occasions where extremely clogged coils cannot be simply flushed and brushed. I have been known to cut coils out of systems and take them to a self serve carwash to clean with pressurized water. In these cases even the best service technicians cannot always bring a coil back to life, so it is not something I would recommend ever trying to do yourself.
Over time in very dusty systems the blower wheel can become caked and therefore less efficient. If you notice this upon inspection you would do well to call a competent professional to take care of the problem. The blower motor is not designed to handle moisture and has to be removed from the housing (after housing is removed from unit) before beginning the cleaning. These shafts have a tendency to rust in place and can raise a good number of 4 letter words from even the most experienced professionals during attempts to remove the motor. If you choose to tackle this task sandpaper for the shaft and a good water displacement oil are key to freeing the shaft- do not in any case use a hammer to pound the shaft; you will be finding yourself replacing a not-so-cheap motor.
Replacing worn parts:
I am not going to go into a schedule for this as the system needs are very broad. If the inconvenience of a minor part breaking at 5:30 on a friday afternoon just before a diner party is intolerable for you, I would highly suggest having a service tech come out to replace any minor parts (transformers, contactors, relays, etc) they deem necessary in the units 5th year of service and every other year after this.
The average life of a central system in my region is about 15 years, with the range being about 10-30 years excluding anomalies. I'll say with high confidence that most equipment can serve you for around 20-25 years if properly maintained, and around 10-15 years if completely neglected. Considering the average PM call is around $200.00 (or 3 hrs for the average homeowner) and system changeout around $7,000, it is certainly a wise investment in either your time or money to perform this simple maintenance annually.
Posted by JD III on
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