During the winter months, one of the most common calls our office receives is that our customers noticed their outdoor unit making strange noises, or they saw smoke coming from the outdoor unit. There is always the possibility that there is indeed a valid issue that needs to be addressed, and if they are indeed seeing smoke, they may need the fire department more than an air conditioning company. So we ask a few more qualifying questions and help them come to the most likely conclusion. Their heating system is a heat pump, and it has gone into “defrost”.
When customers first think they see smoke coming from their heat pump, they are sure the outdoor fan is burning up. This feeling is further enhanced when the motor also stops running. What they are actually seeing is steam. The steam is created by the melting of ice that had built up on the outdoor coil. The outdoor coils tend to frost or ice-up during the winter. This causes the unit to lose efficiency and eventually stop providing heat completely. By regularly defrosting itself, the heat pump runs more efficiently and continually without loss of indoor comfort. When the unit goes into defrost, several things happen. First, the reversing valve shifts from heating mode into air conditioning mode. Temporarily making the outdoor unit the condenser, the hot refrigerant passing through the coils accomplishes the necessary defrosting. This shifting of the reversing valve can make lots of loud and unusual noises. Also, the outdoor fan stops running. This helps build up more heat to melt the ice. At the same time, the supplemental auxiliary heat is energized to temper the otherwise cold air that would be blowing into the house. Once the sensor detects the ice has melted, the system automatically returns to heating mode, the reversing valve re-seats itself for heat, and the fan motor begins running again.
A few decades ago, all of this fancy self defrosting was accomplished with a series of relays, or sometimes even an electric timer and a few thermostatically controlled sensors. Today, the magic of defrost mode is accomplished with a simple circuit board. This board has thermistors that tell the board when it is cold enough to require defrost mode. It also disconnects power to the outdoor fan, and provides/removes power from the reversing valve, depending on the brand.
With all these moving parts, it is not uncommon for something to go wrong. If your outdoor unit resembles the unit pictured above, there is definately cause for concern. The sensors or thermistors can fail so the board will never think it is time for defrost. The board itself can fail and cease sending control voltage where it needs to go. Defrost can operate correctly, but the board fails to send the low voltage control signal to the furnace telling it to activate the auxiliary heater, making it blow ice cold in the home. Lastly, the auxiliary heater may have it’s own failures and not operate, even though the rest of defrost mode is operating correctly.
Whatever the case, Beacon is here to make sure you are comfortable in the warm months, and the cold. Let us know if you are experiencing any of the description above, and we can help set your mind at ease. If it is not operating properly, we would be happy to come evaluate the issue, and get it fixed quickly so you can be comfortable again.
Call us at (352)726-7530.
Beacon Services & Appliances | Beacon Air & Heat, Inc.
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