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Common Compressor Problems & Solutions | HVAC Tips & Tricks

by vs-user on June 8, 2016

HVAC compressor overheating and other problems and fixes

What is a central air conditioning compressor?

Your HVAC compressor is located inside the large outdoor metal cabinet and helps to circulate the refrigerant throughout your entire system. Your outdoor HVAC unit also contains the condenser. (In some A/C units, however, the evaporator, condenser, and compressor are all housed within the same metal container, usually located on the roof or near the foundation).

diagram of air conditioning system

Source: Popular Mechanics

The three main parts of your air conditioning system (compressor, condenser, and evaporator) work together to circulate refrigerant to heat and cool your home. Once the refrigerant evaporates and gets depressurized inside the evaporator, the refrigerant turns into a gas and gets very cold. This cold gas is what absorbs the heat in your home to get discharged outside.

The compressor acts as the middleman between your evaporator and condenser, taking the refrigerant vapor and pressurizing it until it turns back into a liquid. This hot liquid goes to the condenser, where a high-power fan blows air over the condenser coils. With the help from your fan, the refrigerant cools down and goes back to the evaporator, where the entire process begins anew.

The same process applies to the air conditioning system in your car, where heat gets absorbed by the evaporator and gets dumped out via the condenser coils (radiator). The refrigerant travels along insulated tubing.

To learn how your HVAC system works, read this article and watch this video:

Learn how ductless mini-split HVAC systems can heat and cool your home without ductwork.

Common Compressor Problems

1. Overheating

Why is My Compressor Overheating?Overheating is probably the most common cause of compressor failure. If your compressor is running too hot, you can risk a breakdown and expensive repairs. During your annual professional maintenance, your HVAC contractor should check for potential compressor overheating.

To find out if your compressor is overheating, your technician should measure the temperature of the refrigerant discharge line, around 5 inches away from the compressor outlet. Since the hottest part of the compressor (discharge port) isn’t easily accessible, your technician will approximate its temperature based on the readings of the discharge line. A

The hottest location in a refrigeration system is at the discharge port of the valve plate inside the compressor head. It is difficult for a technician to measure the exact temperature at this location. However, measuring the temperature of the discharge line approximately 6 inches from the compressor outlet will give a good indication of the temperature at the discharge port.

There is about a 50-75° drop in temperature from your discharge port to the area your technician measures. Discharge temperatures should never exceed 225°, meaning your discharge port should never go above 300° (300° – 75°).

If temperatures exceed 300°, the refrigeration oil will lose its ability to lubricate your compressor’s cylinder and pistons. Exceeding 350° will cause the oil to break down and contaminate your system. At these temperatures, your compressor is sure to fail.

There are three main reasons why your compressor might be overheating:

  1. High condensing temperatures – this is normally caused by low evaporating pressures which lead to higher compressor discharge temperatures. Possible causes include:
    • dirty condenser
    • high temperatures
    • condenser fan motor malfunction
    • insufficient airflow to condenser
    • overcharged refrigerant
    • wrong refrigerant
  2. Low evaporator pressure/temperature – if your evaporator pressure is low, your compressor will need work extra hard to compress the refrigerant, raising its discharge temperatures. There are many reasons why you might have low evaporator pressure:
    • dirty/iced over evaporator coil
    • dirty air filter
    • insufficient airflow
    • evaporator fan motor malfunction
    • defrost component malfunction
    • undercharged refrigerant
    • wrong refrigerant
  3. High compression ratios – this refers to the ratio between your condensing and evaporating pressures. Since there is a pressure-temperature relationship, the heat of compression will change depending on low or high pressures. If there is a high condensing or low evaporator pressure, the heat of compression will need to increase. To calculate the compression ratio, you need to divide absolute discharge pressure (condensing pressure) by absolute suction pressure. For more information on compression ratios, read this article.

Read more about why your compressor might be overheating here.

2. Frequent Cycling

Compressors can also develop electrical problems. While not the only cause of frequent cycling, a likely culprit is an electrical problem with your compressor. Cycling on and off is a red flag that there is something wrong with your HVAC system. It’s possible that a frayed or worn wire is causing the problem. Call your local HVAC professional to diagnose and fix the situation. Rapid cycling on and off will also cause overheating, possibly leading to a failed start capacitor.

3. Motor Won’t Start (Hard Starting)

A failed compressor motor probably means a faulty start capacitor. The three main motors (compressor motor, blower motor, and outdoor fan motor) all use capacitors to function. Your start capacitor helps to boost the torque of your compressor motor and if it isn’t working, you probably need to replace it. Running an air conditioning system that cycles frequently can lead to more expensive repairs down the road. Call your HVAC technician to have your compressor motor repaired or replaced.

For more air conditioning maintenance advice, read our blogs:

Call Pacific Air Systems for an experience technician to come service or replace your equipment today!

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