How to maintain your heat pump to ensure proper operation and save money.
A heat pump consists of a condenser coil (outdoor), an evaporator coil (indoor), and a compressor that provides heating and cooling to your air handling unit in your home. In warm weather, heat is removed by the indoor coil and carries it to the outdoor coil by circulating refrigerant through the tubing connecting the two. When the outdoor temperatures are cold the opposite takes place. The indoor air is circulated throughout the indoor space using a blower and duct system.
A heat pump system works much the same way as a standard air conditioning system with one exception; a reversing valve is added to change the direction of refrigerant flow. In the heating mode, hot refrigerant is pumped towards the indoor coil where the blower moves indoor air over it. In colder climates, heat pumps are equipped with electric heating coils to provide auxiliary heat when the outdoor temperature is too cold for the unit to work, usually below 30 degree.
Heat Pump Heating and Cooling Cycles
This reverse operation creates some maintenance issues when the outdoor temperatures drop below freezing. Ice can build up on the outdoor coil and reduce the heat pumps' ability to provide the heat. To account for this, heat pumps are designed to run a defrost cycle. Most units use a timer, a thermostat, or a combination of the two to control this process. When the control board determines that a defrost cycle is needed the outside fan is stopped and the reversing valve directs the hot refrigerant to the outdoor coil. This causes the ice to melt and the process is stopped by another thermostat in the outdoor unit.
Causes for Frost
There are several reasons why there might be frost and ice stuck on an outdoor coil of a heat pump.
• bad reversing valve
• damaged outdoor coil
• wiring problem
• bad thermostat
• refrigerant leak
• blocked airflow through the outdoor coil from dirt and debris
• the fan is no longer working
• a fan installed backwards
• fan with incorrect, usually low, RPM
Recommended Heat Pump Maintenance
Replace or wash air filters
Replace or clean your heat pump's air filters in accordance with your manufacturer's recommendations. Ensure that the filters are placed in correct direction of air flow.
As a filter gets dirty over time, it means the blower motor has to work harder to move air through the coil, which means it has to consume more energy and is therefore more expensive to operate. If the airflow is reduced too much, it can cause the compressor to shut done due to high pressure and shorten the life of the equipment.
Check the filters monthly during periods of heavy use such as June-August and October-February.
Clean fins on outside condenser unit
Refer to the owner's manual regarding proper maintenance procedures for your unit. If you have any concerns you should contact a professional HVAC mechanic.
Close up of dirty condenser coils
Shut off the power to the unit.
1. Remove debris from the outside of the unit. Be careful not to press against the coil fins or push debris into the fins.
2. Remove the top fan cage from the top of the unit, there are typically 4 to 6 screws. Clean out any debris that has fallen inside the unit. You can use a shop vac to pick up any small material or use a hose to spray the coils from the inside of the unit.
3. If any of the fins are bent use a fin comb to straighten and clean them.
4. Check the manual that came with the unit to determine if there are oil ports on the condenser fan. Many fans are now designed to be permanently lubricated so this may not be necessary. Never spray any oil or lubricant onto the motor or windings.
Since your heat pump works in the summer and winter, you should check the coils twice per year; in May and September.
Check the Level of the Outdoor Unit
The condenser unit must be level for proper operation. If the unit is not level the compressor and fan can fail prematurely. Check unit for level by:
• Placing a level on the top of the condensing unit and determine if the bubble is within the level lines. Rotate the level 90 degrees and check again.
• The unit should be level in both directions
• If the unit is out of level, raise the low end of the unit with a flat bar to determine how far it needs to be raised. Some units have leveling feet, but you probably need to lift the edge of the concrete pad and add gravel beneath it to form a stable base. You should have someone help you do this.
• If the unit is seriously out of level you may need to replace the concrete pad or blocks.