Ac Unit Freezing Up At Night.

Ac Unit Freezing Up At Night?Find out Why and How to Fix.

Experiencing your ac unit freezing up at night is a common issue for many homeowners, particularly during the sweltering summer months. In this post, we will explore the top five reasons behind this problem and provide guidance on how to prevent it from occurring.

At a glance: Ac Unit Freezing Up At Night due to Insufficient Air Flow,Low Refrigerant Levels,Outside Temperature,Defective Blower Motor or Stuck Contactor.

5 Reasons Why Your AC Is Freezing at Night.

1.Insufficient Air Flow.

One of the leading reasons behind your air conditioner freezing up at night is the presence of dirty or clogged air filters.

When air filters become laden with dust and debris, they obstruct the smooth flow of air through your AC system. This, in turn, can trigger a cascade of issues, with the most critical consequence being the freezing of the evaporator coil.


The evaporator coil is a vital component in your air conditioning system responsible for cooling the air that circulates throughout your home.

When airflow is obstructed due to dirty filters, the temperature of the evaporator coil drops significantly, and this extreme cold can cause it to freeze.

This freezing not only disrupts the cooling process but also poses a risk of potential damage to the coil and other components of your AC unit.

Solution: Regular Filter Maintenance.

To prevent your air conditioner from freezing due to dirty air filters, it’s crucial to implement a simple yet highly effective maintenance routine.

Regularly changing your air filters is the key. Ideally, you should aim to replace them every 30 to 60 days, although the specific frequency may depend on factors like the type of filter and your local air quality.

Also read>>>AC not Cooling Below 75.

Why Regular Filter Maintenance Matters:

  • Efficient Airflow: Clean and unobstructed filters allow air to move freely through your AC system, ensuring it operates efficiently. This, in turn, prevents the evaporator coil from reaching freezing temperatures.
  • Improved Air Quality: Fresh filters help maintain the indoor air quality in your home by trapping dust, allergens, and pollutants.
  • Lower Energy Consumption: When your AC can operate with ease, it consumes less energy, leading to potential cost savings on your utility bills.
  • Extended System Lifespan: By reducing strain on the AC unit, regular filter changes can extend its lifespan, ultimately saving you money on expensive repairs or replacements.

2.Low Refrigerant Levels.

One of the most prevalent reasons for an air conditioner freezing up at night is the insufficient presence of refrigerant.

When your AC system lacks an adequate amount of refrigerant, it struggles to absorb the necessary heat from your home, ultimately resulting in the freezing of the coils.

Also read>>>AC Unit Blowing Hot Air Outside.


Refrigerant is the vital substance responsible for the cooling process within your air conditioner. It works by absorbing heat from the indoor air and releasing it outside.

However, when the refrigerant levels are too low, the system’s efficiency is compromised. This leads to the evaporator coils becoming excessively cold, eventually causing them to freeze over.

Solution: Professional Inspection and Recharge

If you suspect that your air conditioner is experiencing low refrigerant levels, it’s imperative to seek the expertise of a professional HVAC technician. Attempting to address this issue without the necessary knowledge and equipment can lead to further complications. The technician will conduct a thorough inspection of your system to identify any leaks or issues and subsequently recharge the system with the appropriate amount of refrigerant.

Why Professional Intervention is Essential:

  • Identifying Leaks: A professional can pinpoint the source of the refrigerant loss, which may be due to leaks or other problems within the system. Repairing these leaks is crucial to prevent further refrigerant loss.
  • Correct Refrigerant Type: HVAC technicians have the expertise to choose the right type of refrigerant for your specific AC unit, ensuring optimal performance and efficiency.
  • Preserving System Efficiency: By addressing low refrigerant levels, your air conditioner can once again operate efficiently, cooling your home without freezing the coils.

3.Outside Temperature

The external temperature can play a pivotal role in causing your air conditioner to freeze up, especially at night. When the outdoor temperature decreases significantly, it affects your AC’s evaporator coil.

The cold ambient temperature can lead the coil to become excessively cold, causing moisture to freeze on its surface and subsequently obstructing the airflow.


The evaporator coil in your air conditioning system is designed to cool the warm air that passes over it. However, when the outside temperature is considerably low, the coil’s temperature can drop to the point where it causes condensation or moisture in the air to freeze upon contact.

This frost buildup can restrict the flow of air through the coil and result in freezing, affecting the AC’s performance.

Solution: Regular Maintenance and Proper Sizing.

To prevent your air conditioner from freezing due to outdoor temperature drops, several key measures should be taken:

  • Regular Maintenance: Scheduled maintenance by a professional HVAC technician can ensure that your system is in optimal condition and better equipped to handle varying weather conditions. Technicians can identify and address issues that might contribute to freezing, such as dirty coils, refrigerant levels, or airflow obstructions.
  • Proper Sizing: Ensure that your AC system is adequately sized for your home and the local climate. An AC unit that is too large for your space may cool too quickly, leading to short cycles and inadequate dehumidification, potentially increasing the risk of freezing. On the other hand, an undersized unit may run continuously, struggling to meet the cooling demands and potentially freezing the evaporator coil.

4.Defective Blower Motor.

Another potential cause for your air conditioning system freezing up at night is a malfunctioning blower motor. The blower motor plays a crucial role in circulating air through your AC system.

When it fails to function correctly, it disrupts the airflow, causing the evaporator coil to become excessively cold and ultimately leading to freezing.


The blower motor is responsible for drawing warm air from your home, passing it over the evaporator coil for cooling, and then distributing the cool air back into your living spaces.

However, when the blower motor is defective, it cannot adequately circulate air. As a result, the evaporator coil’s temperature drops significantly, leading to the accumulation of frost and freezing.

Solution: Professional Diagnosis and Repair.

If you suspect that your blower motor is not functioning properly, it is imperative to seek the expertise of a professional HVAC technician to diagnose and rectify the issue.

Attempting to address a defective blower motor without the necessary knowledge and tools can lead to further complications.

Why Professional Assistance is Essential:

  • Accurate Diagnosis: HVAC technicians have the skills and equipment to accurately diagnose blower motor issues, which can encompass a range of problems such as motor failure, electrical issues, or debris obstructions.
  • Effective Repairs: They can perform the necessary repairs or replacements, ensuring that your blower motor is back in proper working order, thereby allowing your AC to function as intended.
  • Preventative Maintenance: HVAC professionals may also provide guidance on preventative maintenance practices to extend the lifespan of your blower motor and prevent future issues.

5.Stuck Contactor.

A stuck contactor is another potential factor leading to your air conditioner freezing up during the night. The contactor is a critical component responsible for initiating the on/off cycles of your AC.

When it becomes stuck in the “on” position, your AC operates continuously, eventually causing the evaporator coil to freeze.


The contactor is akin to a switch that regulates the flow of electricity to your air conditioner. It is designed to cycle the AC system on and off as needed to maintain a comfortable indoor temperature.

However, when the contactor becomes stuck in the “on” position, it fails to break the electrical connection, resulting in continuous operation of the AC. This leads to a significant drop in temperature on the evaporator coil and eventual freezing.

Also read>>>Heat Pump Freezing Up.

Solution: Professional Inspection and Repair.

If you suspect that your contactor is stuck, it is imperative to contact a professional HVAC technician to inspect and repair the issue.

Attempting to address a malfunctioning contactor without the necessary expertise can result in further complications.

Why Professional Assistance is Crucial:

  • Accurate Diagnosis: HVAC technicians can accurately diagnose the issue with the contactor and determine whether it is indeed stuck in the “on” position. They can also check for potential underlying problems, such as electrical issues or worn contactor components.
  • Effective Repairs: Professionals are equipped to perform the necessary repairs or replacements, restoring the proper functioning of the contactor. This will ensure that your AC cycles on and off as needed, preventing the evaporator coil from freezing.
  • Preventative Measures: HVAC technicians may offer guidance on routine maintenance practices to prevent future contactor issues and extend the overall lifespan of your AC system.

Frequently Asked Questions (FAQs).

Why is my ac unit freezing up at night?

There are several potential reasons for your ac unit freezing up at night. One common cause is dirty or clogged air filters, which restrict airflow and lead to the evaporator coil becoming too cold.

Low refrigerant levels can also trigger freezing as the system cannot absorb enough heat. Furthermore, outdoor temperature drops can cause moisture to freeze on the evaporator coil, and a defective blower motor may disrupt airflow, contributing to freezing.

Finally, a stuck contactor can result in continuous AC operation, ultimately causing the coil to freeze.

How can I prevent my air conditioner from freezing at night?

To prevent your air conditioner from freezing, consider the following:

  • Regularly change your air filters every 30 to 60 days to ensure proper airflow.
  • Schedule professional HVAC maintenance to address issues like low refrigerant levels or dirty coils.
  • Properly size your AC unit for your home and local climate to handle temperature fluctuations.
  • Seek professional assistance if you suspect a defective blower motor or a stuck contactor.

Can I fix a freezing air conditioner issue myself?

While you can perform routine tasks like changing air filters, diagnosing and repairing issues that lead to AC freezing, such as low refrigerant, defective components, or a stuck contactor, generally require the expertise of a professional HVAC technician.

Attempting to address complex problems without the necessary knowledge and equipment may lead to further complications.

How do I know if my contactor is stuck?

If your contactor is stuck, your air conditioner will run continuously, regardless of the desired temperature.

To determine if the contactor is the issue, it’s crucial to contact a professional HVAC technician for a thorough inspection. They can diagnose the problem accurately and perform the necessary repairs or replacements to restore proper operation


Understanding the causes of ac unit freezing up at night is crucial for maintaining a comfortable indoor environment.

Factors such as dirty air filters, low refrigerant levels, outdoor temperature drops, defective blower motors, and stuck contactors can all contribute to this issue.

Regular maintenance and proper sizing of your AC unit are essential preventive measures. However, addressing these problems often necessitates professional expertise to accurately diagnose and repair complex issues.

By maintaining your air conditioner and seeking professional assistance when needed, you can ensure that your AC operates efficiently and reliably, allowing you to enjoy a cool and comfortable environment, even on the hottest summer nights.