Why Your Heat Pump Is Not Defrosting

Using a heat pump is an efficient way to keep warm during the cold season. Unfortunately, the low temperatures can freeze the heat pump's outdoor unit, specifically the condenser, and prevent further heat exchange. Heat exchange impairment reduces heating efficiency and risks damage to the heat pump. The heat pump uses an on-demand defrosting cycle to melt the frost.

Below are some reasons your heat pump might not defrost.

Sensor Malfunction

The heat pump has a sensor at the bottom of the outdoor unit. The sensor detects the temperature and triggers the defrost cycle if the temperature is freezing. The defrost cycle won't start if the sensor has erroneous readings. That might happen if the sensor malfunctions. One way this can happen is if an external source, such as direct sunlight, heats the sensor.

Electrical and Electronic Problems

The heat pump's electrical and electronic system controls the defrost cycle. For example, a typical heat pump uses:

• A timer to control the heat cycle's frequency
• A relay to trigger the reversal of the heat pump's operation
• Electricity to power all the electrical and electrical functions

Thus, problems with the electrical and electronic systems can lead to defrost failure. For example, the compressor won't run if it doesn't have power due to a damaged cable. Similarly, a malfunctioning relay interferes with the defrost cycle even if other system parts are functional.

Malfunctioning Reversing Valve

The reversing valve is a critical component of the heat pump, enabling it to provide both heating and cooling functions. The reversing valve changes the refrigerant's path between the indoor and outdoor coils. The refrigerant moves from the outdoor to the indoor coil during the heating mode. The refrigerant's movement reverses during the cooling cycle.

The heat pump releases heat to the outdoor coil during the defrost cycle. However, that won't happen if the reverse valve malfunctions and the heat pump continues to release heat indoors. For example, the refrigerant flow direction won't reverse if the valve sticks in the heating mode.

Damaged Outdoor Fan

A heat pump has an outdoor fan that circulates air and facilitates heat exchange. The air circulation helps the coil to absorb heat from the outside air so that the refrigerant can take it outside. Thus, the outdoor fan usually stops running during the defrost cycle when the heat pump's outdoor unit doesn't need to absorb heat.

A malfunction of the outdoor fan system might allow it to run even during the defrost cycle. A damaged fan motor or damaged capacitor can cause such malfunctions. The problem might not be serious if the coil is not seriously frosted. However, the fan might dampen the defrosting efficiency if the weather is too cold and ice has clogged the outdoor unit.

Low Refrigerant

The heat pump uses refrigerant to carry heat between the outdoor and indoor coil. During the defrost cycle, the refrigerant carries heat to the outdoor coil, which warms and melts the frost. Thus, the defrost cycle is impossible if the heat pump doesn't have enough refrigerant to heat the outdoor cycle.

Low refrigerant pressure is often the result of refrigerant leakage. For example, refrigerant lines can leak due to corrosion, accidental damage, or wear and tear. In extreme cases, the refrigerant pressure might drop so low that the heat pump stops working.

Hopefully, your heat pump won't suffer serious issues that might affect its operation, such as defrost cycle failure. Contact Wyoming Air if you suspect that your heat pump has malfunctioned. We have decades of experience in the HVAC industry. We will diagnose and fix the problem so your home can be warm again.