OUTDOOR UNIT FREEZING-UP - The outdoor unit forms an abnormal amount of ice on the outdoor coils that does not go away after an hour. * It is normal for a heat pump to develop frost on the outdoor coil during cold temperatures.  A normal defrost cycle should take place to thaw the coil.  During defrost mode the outdoor fan motor stops, the reversing valve switches into cooling mode and the compressor continues to operate.  It is normal to see steam coming out of the outdoor unit during a defrost cycle. POSSIBLE PROBLEM & DESCRIPTION Ice Covering Top of Unit It is not unusual after freezing rain or snow thawing for water to freeze over the top of the fan discharge of the outdoor unit.  This can either stop the fan from turning or prevent air from discharging from the unit.  In either case, the ice needs to be removed for the unit to function properly. Do not try to remove ice or any other objects from the fan path with power on the unit.  Always pull the service disconnect switch near the unit or turn off the breaker before attempting any repairs.

It may be necessary to switch the thermostat to "Em Heat" until the unit thaws or repairs are made. Failed Outdoor Fan - Qualified Technician Recommended If the outdoor fan motor quits running while a heat pump is operating in the heating mode, the outdoor coils will quickly freeze and a defrost cycle may fail to remove all of the ice. A stopped fan motor can be the result of a bad motor, bad start capacitor (below), or faulty control board or relay. Bad Capacitor - Qualified Technician Recommended Low Freon - Qualified Technician Recommended If a heat pump becomes low on refrigerant it may not be able to produce enough heat in a defrost cycle to thaw the outdoor coil.  This would be seen in a heat pump that enters and stays-in defrost mode for about 10 minutes and then exits defrost with a substantial amount of frost or ice still covering the coil. Bad Defrost Control - Qualified Technician Recommended There are two types of defrost controls - Time & Temperature or Demand Defrost.

Time & Temperature controls use a defrost thermostat and a timer board. Time & Temperature boards typically have a setting for 30, 60 or 90 minutes.  When the coil temperature drops below 30 degrees a defrost thermostat should close, starting the timer on the board.  After the selected time period the control board should initiate a defrost cycle. Demand Defrost boards measure the outside air temperature and the coil temperature to determine the optimum conditions for a defrost cycle to take place. Bad Defrost Sensor/Thermostat - Qualified Technician Recommended The defrost thermostat should "close" when the coil temperature is below 30 degrees.  A bad defrost thermostat will prevent a Time & Temperature defrost control from entering a defrost cycle. Either a bad outdoor sensor or coil sensor can cause a Demand Defrost control to not defrost properly.This article was crafted with the help of Mike Costa from Perfect Home Services The inner workings of HVAC systems can be perplexing to many people, but finding ice on a heat pump during the hot summer months will surely spark confusion among even the savviest homeowners.

Thankfully, there are precautions that homeowners can take to avoid having their heat pumps freeze over during any season. Mike Costa, Technical Supervisor with Perfect Home Services in Chicago, offers his expertise on how to keep your heat pump free of ice and running smoothly. While many homeowners have separate units for heating and cooling, a heat pump uses the traditional mechanisms of an A/C unit to provide both. During the summer, a heat pump operates just like a standard air conditioner. air handling unit control diagramIn the winter, the heat pump takes in energy from outside and provides heat to your home by using a reversing valve that redirects the flow of refrigerant. air conditioning unit noiseWhen used in the right climates, heat pumps can be very energy efficient because they heat your home using electricity and refrigerant instead of burning fuel with a traditional gas furnace.split air conditioner in india compare

However, Mike warns that recurring freezes can damage a heat pump, so it’s important for homeowners to know how to avoid and treat heat pump freezes. “When a unit starts to freeze, you actually start to slug liquid back into the compressor, and you don’t cool the compressor properly,” says Mike. “This can cause severe damage to the compressor itself.” Replacing a compressor can be very costly and will likely waste any money saved on energy bills. Common Causes of Heat Pump FreezesMike explains that heat pumps work best in “climates that do not get below around 32 degrees ambient temperature.” But even homeowners living in the ideal climates for a heat pump will have to endure occasional drops in temperature. During cold spells, look for the accumulation of ice on coils and Freon lines, says Mike. Many types of heat pumps have a defrost cycle to combat brief periods of below-freezing temperatures, but Mike warns that any prolonged icing will inhibit airflow and potentially damage your system.

Unfortunately, many things that can go wrong in an installation will block airflow and consequently cause your heat pump to freeze. Mike says that mismatching is a common problem when heat pumps are installed, making it especially important to work with reputable contractors. Oftentimes “the wrong-sized coil is put with the wrong-sized pump; the wrong-sized heat pump is put with the wrong-sized blowing motor in the furnace; or the Freon lines are not sized correctly,” says Mike. Hiring a knowledgeable professional will ensure that your heat pump has the correctly sized components to provide year-round comfort in your home.Heat pumps become susceptible to icing when the refrigerant levels are too low. A perfectionist when it comes to HVAC, Mike says that “there’s a right level for refrigerant. A lot of guys will read it as being ‘close enough’ to the perfect level.” Low refrigerant levels can also cause problems with the compressor by forcing it to work overtime. You must be EPA certified to work with refrigerants, so always call in a professional to check these levels.

Mike says that homeowners can identify a freezing problem if they either visually inspect their unit for ice or notice a problem with airflow in their homes. Airflow problems will typically result in your home not heating or cooling as it normally does, Mike notes. Remember that freezing can occur in either the winter or summer, so if your home does not feel as if it is cooling properly on a boiling summer day, don’t rule out the possibility of ice on your heat pump. Ways to Avoid a Heat Pump Freeze Have an annual inspection. While we unfortunately cannot control the weather, there are many preventative measures that homeowners can take to avoid heat pump malfunctions that cause icing. Mike says that “during a maintenance visit, the refrigerant levels are going to be checked, the coils are going to be cleaned, the electrical components are going to be checked, and the fan motors will be inspected.” Without periodic inspections, your heat pump will be vulnerable to recurring freezes, which Mike says can severely damage your system.

Consider a hybrid heat pump. Heat pumps are not typically recommended for climates that experience frequent freezes, but many homeowners would still like to avoid using their furnace as much as possible to save on energy costs. According to Mike, hybrid units are increasing in popularity because they “use the heat pump until the weather reaches freezing temperatures, and when it gets lower, there’s another controller that automatically kicks in the furnace for backup.” For those living in extreme cold, heat pumps designed specifically for cold climates are promising options, but they are still in the early stages of development and implementation. Be advised that you should never attempt to fix a heat pump yourself. Not only do you have to be EPA certified to work with refrigerants, but “you can really get hurt,” says Mike. “Depending on the heat pump, particularly newer ones, there are high-pressure gases inside the Freon levels, not to mention its high electrical charge.”