Explaining Superheat and Subcooling to Your Apprentice!

Summary

In this instructional video, Crema Glasha from AC Suburbs Tech explains the concepts of superheat and subcooling in air conditioning systems to an apprentice. She outlines the necessary equipment, identifies the appropriate valves for measuring each, and uses color-coded gauges for clarity. Glasha elaborates on the process of subcooling in the condenser coil and superheat in the evaporator coil, emphasizing their importance for refrigerant charge assessment. She also discusses the significance of these measurements for systems with thermostatic expansion valves and fixed orifice metering devices, providing practical advice for troubleshooting and maintaining air conditioning systems.

Takeaways

• 🔧 Subcooling is measured at the outdoor unit's surface valve, which is the liquid line service valve.
• 📏 Subcooling refers to the reduction in temperature of liquid refrigerant as it passes through the condenser coil.
• 🌡️ To measure subcooling, you need to take a pressure reading and convert it to a saturated temperature, then take an actual temperature reading on the liquid line.
• 💧 Subcooling is used to check the refrigerant charge level in systems with a thermostatic expansion valve (TXV).
• 🌡️ Superheat is measured at the indoor evaporator coil and involves checking the vapor line with a blue gauge.
• 🔄 Superheat is the increase in temperature of the refrigerant as it changes from a liquid to a gaseous state in the evaporator coil.
• 📊 To measure total superheat, you take a pressure reading on the large vapor line and a temperature reading on the line within a few inches of that port.
• 📈 The target superheat can be determined using a psychrometer for indoor wet bulb and outdoor dry bulb temperatures, or with a digital manifold.
• 🛠️ For systems with a fixed orifice metering device, like a capillary tube, you check the refrigerant charge with the total superheat method.
• 📚 The script recommends using a book and quick reference cards for detailed guidance on refrigerant charging and troubleshooting.
• 🔄 The TXV helps maintain a steady superheat by adjusting the refrigerant flow, making subcooling the key measurement for systems with a TXV.

Q & A

What is subcooling and how is it measured?

Subcooling is the lowering of the liquid refrigerant's temperature in the condenser coil. It is measured at the outdoor unit surface valve, which is the liquid line service valve. The measurement involves taking the pressure reading at the valve and converting it to a saturated temperature using a pressure-temperature chart. Then, a temperature reading is taken on the liquid line, and subcooling is the difference between the saturated temperature and the actual line temperature.

What is the significance of the red and blue gauges in an air conditioning system?

The red gauge is used for measuring subcooling on the high-pressure side of the system, which involves the liquid line. The blue gauge is used for measuring superheat on the low-pressure side, which involves the vapor line.

How does the size of the vapor and liquid lines relate to their functions?

The vapor line is always larger than the liquid line because it needs to accommodate the increased volume of refrigerant as it vaporizes.

What is the purpose of the condenser coil in an air conditioning system?

The condenser coil's purpose is to reject heat from the high-pressure vapor refrigerant. As the refrigerant travels through the coil, the condenser unit draws air across the coil and expels hot air, thus cooling the refrigerant.

What is superheat and where is it measured?

Superheat is the increase in temperature of the refrigerant as it absorbs heat in the evaporator coil. It is measured at the indoor evaporator coil, specifically on the vapor line using the blue gauge.

Why is it important to measure subcooling and superheat?

Measuring subcooling and superheat is crucial for checking the refrigerant charge level in an air conditioning system. It helps to determine if the system is overcharged or undercharged and aids in troubleshooting.

How does a thermostatic expansion valve (TXV) relate to subcooling measurements?

A TXV is a regulating metering device that adjusts the amount of refrigerant entering the evaporator coil. When measuring subcooling, it's important to get the measurement as close as possible to the target subcooling reading on the rating plate of the system, which helps in maintaining the correct refrigerant charge level.

What is the difference between a thermostatic expansion valve (TXV) and a fixed orifice metering device?

A TXV can open and close to regulate the refrigerant flow based on the superheat, while a fixed orifice metering device, like a capillary tube, has a fixed hole size and does not adjust.

Why is the total superheat method used for systems with a fixed orifice metering device?

For systems with a fixed orifice metering device, the superheat can fluctuate because the amount of refrigerant entering the evaporator coil remains constant. Therefore, the total superheat method is used to check the refrigerant charge.

How do you determine the target superheat for a system with a fixed orifice?

You take an indoor wet bulb reading and an outdoor dry bulb temperature reading, then use a superheat chart to determine the target superheat. Alternatively, you can use a digital gauge set or a target superheat app.

What are the steps to troubleshoot a frozen evaporator coil?

The steps to troubleshoot a frozen evaporator coil include checking the refrigerant charge, airflow, and ensuring the system is clean and free of blockages. The script suggests referring to the provided book or quick reference cards for detailed steps.