Thursday, June 9, 2016

It’s Hot – What’s Wrong with my AC?

When the weather turns warm is when we discover that the air conditioning is not working properly or simply not working at all. According to the U.S. Department of Energy 6% of the average home’s energy use goes to cooling. Only two thirds of homes in the United States have air conditioners; fewer still have central air. Here in the south, our air conditioning bills are probably higher and most homes built in the last decades have central air conditioning.

The most common types of central air conditioning systems currently in use are the air heat pump and the conventional air conditioner. Heats pumps are used in more moderate temperature zones. In a dependability survey of over 16,000 members Consumer Reports found that the most likely parts to fail are the evaporator coils and the controls on both types of systems. Air heat pumps are also prone to have the compressors or the condenser coils fail. According to the Department of Energy, the most common air conditioning problems are:

Refrigerant. The refrigerant could be low and this could be from a slow or not so slow leak and is usually a symptom of the evaporator coils failing. The leak needs to be identified and repaired before the system is recharged. Some typical places to find leaks are the unit pressure ports, weld/braze connections, or places where rubbing has produced a hole in the tubing. Unless there is a leak from somewhere the system should never need to have the refrigerant recharged- it does not get used up.

R-22 (also known as HCFC-22) had been the refrigerant of choice for residential heat pump and air-conditioning systems for more than four decades. Unfortunately for the environment, releases of R-22, from leaks, contribute to ozone depletion and R-22 is being phased out as part of the international agreement to end production of HCFCs, new residential air conditioning systems are now designed to use more ozone-friendly refrigerants typically R-410a.

The Department of energy also identifies compressor and fan controls as areas likely to fail. The other common problems identified by the Department of Energy are routine maintenance issues that have been ignored. Check those first before calling a service company.

Sensor and Thermostat Issues. Window units have sensors that can be knocked loose when installing a window unit. Check them. For central air systems, check the thermostat to make sure that it is set into air conditioning mode and the correct temperature is set. This is a simple mistake that happens. One of my thermostats toggles between air conditioning mode and heating mode, but my heat pump needs to be set to the correct mode. I have trained my family not to touch.

Drain line blockage. The drain line from the ac unit can get clogged and prevent the system from working properly. Also, the filters might need to be changed. A clogged filter restricts airflow through the unit reducing its ability to effectively cool. This can seem like the system is low in refrigerant, but is easily fixed by replacing the filter. Pull the filter and see if it’s dirty. These are the easy things to fix.

According to the data collected by Consumer Reports 31%-50% of heat pumps are likely to have a failure or serious breakage at five years depending on brand. That is quite a difference and if you are going to replace your heat pump this year, you might what to check the Consumer Reports reliability data before purchasing a new system. My last heat pump had an evaporator coil failure at 5 and half years. At that time I replace the system rather than pay $2,500 to repair a heat pump that I was not satisfied with. Most surveys have found that the average life of a heat pump is between 8 and 15 years. Heat pumps operated all year long and do not last as long as matched conventional systems. For conventional central air conditioning units, 20%-30% of the systems are likely to fail at five years. You will need to determine for yourself the cut-off point for repair or replace.

An air heat pump is usually a split heat-pump systems consisting of two parts: an indoor (coil) unit and an outdoor (condensing) unit. Both units are designed to work together. Heat-pump systems manufactured today, by law, must have a seasonal energy efficiency ratio (SEER) of 13 or higher depending on what part of the county you live in. Beginning this year the federal standards differ by region with central air conditioning systems in the South and Southwest required to meet stricter standards than those installed in the North. The new yellow Energy Guide label now includes a map of the U.S. indicating where the equipment can be installed.
from DOE
Seasonal Energy Efficiency Rating (SEER) or Heating Seasonal Performance Factor (HSPF) for heat pump systems are the efficiency ratings on heat pumps, the higher the SEER/HSPF, the more efficient the equipment. The SEER is measured in average Btu output over the season divided by the watt hours and is the standard measure of energy use efficiency. The Air Conditioning, Heating and Refrigeration Institute (AHRI), defines the method and conditions to measure SEER, and they are not realistic in the humid south. However they are a good measure of relative efficiency. Generally, the higher the SEER/HSPF of a unit, the higher the initial cost and lower the operating cost. For a high-efficiency systems to work properly, the outdoor unit and indoor unit must be perfectly matched, properly sized and correctly ducted to deliver the right air flow.


  1. This is a very thorough and comprehensive list of things to try when your air conditioner is not working. I worked as an HVAC technician for many years in the hot south and these are many of the common problems we would run into every summer. I have also trained my family to leave the thermostat alone!

  2. I would have guessed that there would have been a larger number of homes that had air conditioners or central air. I guess it makes sense that only homes in certain areas of the country actually need that service compared to the number of homes that have a heating service.