Important tips and information about starting up your air conditioner for this year's cooling season.
One of the best ways to save money and reduce the chance for equipment failure is to remove dirt and debris that has clogged the cooling fins of your air conditioner and lowered its efficiency. A dirty air conditioner may even stop cooling altogether. Many contractors suggest that over half of all air-conditioner failures were the result of the owner’s failing to clean them.
Most central air conditioners have two basic parts: an outdoor unit (compressor/condenser) that sits next to your home and an indoor unit (evaporator) that’s located inside a central duct near your furnace. If you have a heat pump instead of a furnace, the indoor unit will be in the air handler.
Heat pump system – Source Toolbase Services
Central Air Conditioning System
Refrigerant in the copper tubes absorbs heat at the evaporator coil inside, cools indoor air and then releases heat at the condenser coil outdoors.
Contrary to popular belief, air conditioners do not consume refrigerant as a car consumes oil, so under ideal conditions it would never need changing or filling. A low refrigerant level indicates a leak which should be repaired before adding more. While most new system connections are brazed (brass welds) to minimize leaks, many older units, over 10 years, were connected with mechanical flared fittings which can vibrate loose over the years, causing leaks.
Refrigerant leaks are problematic because:
1. Low refrigerant levels reduce efficiency of the air conditioner.
2. They can freeze the evaporator (inside) coil, causing it to ice up and block airflow.
3. Refrigerants are an Environmental Protection Agency (EPA) controlled substance, deemed hazardous if released into the environment. Only licensed professionals are allowed to purchase it and must reclaim old refrigerant.
4. The heart of the unit is the compressor that is cooled by the refrigerant. Over time, low refrigerant levels can cause overheating and premature failure of the compressor. This will require a complete replacement of the compressor or the entire condensing unit - a very expensive proposition.
The Most Important Step: Clean the Outdoor Unit
Two copper tubes connect the outdoor compressor and its condenser coil (a “coil” is a combination of fins and tubes) to the indoor evaporator coil that’s located in the plenum above the furnace blower. One tube is covered with foam insulation. If you have a heat pump, both tubes will be insulated.
The fan inside the condenser coil sucks air through the fins and blows it out the top of the unit. As a result, the fins act like a filter as the fan pulls dirt and debris through the coil. Dust, leaves, dead grass and anything else that collects on the fins will block airflow and reduce the unit’s efficiency. Grass clippings, tree pollen, and dandelions are the most common offenders. You might have to clear the fins weekly or even daily during the spring season.
Always begin by shutting off the electrical power. Then proceed with the cleaning.
Disconnects should be located outside within three feet of the condenser unit. They will either be a switch type or a plug type. If it is a plug type, you will need to lift the cover and pull out the plug to disconnect the power.
Some fan motors have lubrication ports; apply five drops of special oil for electric motors, not penetrating or all-purpose oil. You can find oil for electric motors at your local hardware store or home center. Many fan motors are maintenance-free and can’t be lubricated. Check your owner’s manual to make sure.
The compressor and its motor sit inside the coil. They’re usually sealed and won’t need maintenance. Check for oil drip marks on the bottom of the compressor case or pad. This indicates an oil leak; the compressor or tubing might be leaking refrigerant as well. Sealed systems have oil that runs through the same tubing that the refrigerant uses to lubricate the compressor. If you find a leak or feel oil around brazed fittings, call an HVAC contractor to inspect the system and repair any leaks found.
Important Outside Startup Guidelines
Some compressors can be fragile so to prevent any damage which would require expensive repairs, follow these steps when restoring the power:
If the 240-volt power to your compressor has been off for more than four hours, don’t start the outdoor unit immediately after cleaning. Instead:
1. Move the switch from “Cool” to “Off” at your inside thermostat.
2. Switch the 240-volt power back on and let the outdoor unit sit for 24 hours. This allows the crankcase heater to heat the compressor’s internal lubricant. Feel your compressor before you switch the thermostat to “Cool” to verify that the compressor is warm to the touch. If it isn’t, you may need to replace the crankcase heater. Sometimes they are clamped onto the exterior of the compressor and easily replaced.
3. Switch the thermostat to its cooling mode and set the temperature so that the outdoor unit comes on. Then check the outdoor unit.
If you switch off the air conditioner at the thermostat at any time, wait at least five minutes before switching it back on. Once off, the compressor needs time to equalize the pressure inside the system. If you restart it too soon, you can stress the motor. Many thermostats have automatic time delays built into the circuitry to protect the compressor from this problem.
Clean the outdoor unit when the temperature is 60 degrees F or higher. Compressors won’t work properly in temperatures below 60 degrees unless they are equipped with low-ambient controls. Most units do not have this control, which slows the condenser fan speed or delays the start up of the fan. In most systems the compressor and fan start simultaneously and in cooler weather this can overcool the compressor and cause it to shut off due to low pressure.
Clean the Indoor Unit
The blower compartments of newer furnaces are so tight that you usually can’t lubricate the blower. Have a pro do it during periodic furnace maintenance.
The evaporator coil in the plenum dehumidifies your indoor air as it cools it during the summer. The water that condenses on the coil flows out through a condensation tube. Check it to make sure the tube isn’t clogged by sludge and algae, especially at the drain port. A flexible tube is easy to pull off and clean, but you might have to saw off a rigid plastic tube with a hacksaw to check it. Then weld it with the proper pipe joint solvent and coupling.
Conduct a Test Run
Some time in the spring, start your system and let it run for up to an hour. If you can identify problems early, you'll find HVAC contractors may be readily available and won’t have to pay a premium for a service call. Wait till the first 90-degree day and you may end up on a waiting list and paying a lot more.
Here are a few terms that HVAC contractors frequently use that you should be aware of to help you understand how your system works.
Bin Method - The Bin Method is used for properly sizing heating and cooling equipment for larger buildings. This method breaks down the temperatures for each month into bins and allocates the average number of hours in each month into each bin. This data is then entered into a formula that includes the area of the exterior of the building, the overall R-value, and the temperature difference.
q = A x ΔT/R for heat loss
q = A x CLTD/R for heat gain
Degree-Day –This is calculated by subtracting the average outdoor temperature for an area from 65 dF. This measurement is used to estimate the amount of heating or cooling a home or building will need. A simplified example; if on day the temperature is 95 dF, then that equals 30 cooling degree days (CDD). If the temperature is 50 dF, then that would equal 15 heating degree days (HDD). The actual number is calculated by dividing the day into 30-minute increments and added together for the day. The temperature is recorded from a weather station and added to or subtracted from the base temperature, typically 65 dF.
This is used to compare weather conditions from year to year and not for design purposes.
A few websites where you can find your HDD or CDD are here:
Latent Heat - A type of heat that when added to an area produces an effect other than an increase in temperature. This typically represents humidity or moisture added to the air. Latent means hidden, so a thermometer cannot measure this type of heat.
Sensible Heat - Heat added or subtracted that causes a change in temperature, measured with a thermometer.
Ton - One ton of refrigeration is equal to 12,000 BTUs per hour. Some contractors will say you need a 3-ton unit, this would equal 36,000 BTUs. A typical window AC unit is about 9,000 BTUs.
Wet Bulb Thermometer - A thermometer that measures the relative humidity in the air, used to determine latent heat.