Common Relays Used in HVAC/R!

Summary

In this HVAC tutorial, Creme McGladrey, sponsored by Danfoss, explains the function and types of relays used in HVAC systems. He clarifies that not all switches are relays, highlighting the role of sequencers and thermal overloads. McGladrey details the operation of various relays, such as current starting, potential, fan control, and general-purpose relays, explaining their unique functions and how they are used in control boards. The video also includes troubleshooting tips and resources for further learning.

Takeaways

• 🔌 A relay operates by using a copper coil that turns into an electromagnet when powered, which opens and closes contacts.
• 🚫 The video script clarifies that a sequencer and thermal overloads are not relays, as they do not use electromagnetism to operate.
• 🔩 Sequencers use a heater plate to flex a thermal disc, which closes contacts, unlike relays.
• 🌡️ Thermal overloads and PTC thermistors are explained as devices that use thermal mechanisms to protect compressors, not as relays.
• 🔄 Potential relays are used to disconnect start capacitors from a compressor once it's running, aiding in the startup process.
• 🌀 Current starting relays assist in starting a compressor by temporarily closing contacts to allow high current to the start winding.
• 💨 Fan relays control the operation of fans in HVAC systems, with different amperage ratings for different fan sizes.
• 🔧 Contactors are similar to relays but are used for higher amperage applications, with multiple poles that can be connected or disconnected simultaneously.
• 🔄 ICE Cube relays are plug-in type relays that have specific voltage and amperage ratings for their operation.
• 🛠️ The video provides insights into various types of relays used in HVAC systems, including their functions and how they differ from other similar components.
• 🔍 Troubleshooting guides and tools for working with relays in the field are available for further learning and application.

Q & A

What is the basic function of a relay in HVAC systems?

A relay uses a copper coil that, when powered, turns into an electrical magnet to open and close contacts, allowing for the control of various components in HVAC systems.

Why are the devices discussed in the script not considered relays?

The devices mentioned, such as sequencers, thermal overloads, and flame rollout switches, do not use electrical magnetism to operate; instead, they rely on thermal discs or PTC thermistors for their operation.

How does a sequencer operate differently from a relay?

A sequencer operates using a heater pan to flex a thermal disc, which then pushes up on rods to close contacts, unlike a relay that uses an electrical magnet to control contacts.

What is the purpose of PTC thermistors in HVAC systems?

PTC thermistors are used to help start compressors. They have a resistance that increases as current is drawn through them, to the point where they open up the electrical circuit to prevent overload.

How does a current starting relay assist in starting a compressor?

A current starting relay temporarily closes the connection between start and run taps when the compressor starts, allowing high current to flow to the start winding, which helps the compressor start up.

What is the role of a potential relay in an HVAC system?

A potential relay is used to disconnect the start capacitor once the compressor has started, ensuring that the capacitor does not remain in the circuit and potentially cause damage.

What are the different types of relays mentioned in the script, and what are their specific uses?

The script mentions fade relays, current starting relays, potential relays, general-purpose relays, multi-purpose relays, and fan relays, each serving different functions such as starting compressors, controlling fan operation, and managing electrical circuits.

How do contactors differ from relays?

Contactors are similar to relays but are designed to handle higher currents and voltages. They have multiple poles that can connect and disconnect simultaneously, making them suitable for controlling larger loads.

What is the significance of the FLA rating on a contactor?

The FLA (Full Load Ampere) rating indicates the maximum current that a contactor can safely handle. It is crucial to match the FLA rating when replacing a contactor to ensure safe operation.

What is the purpose of a flame rollout switch in an HVAC system?

A flame rollout switch uses a thermo disc to manually reset the system in case of a flame rollout, ensuring safety by preventing the system from operating without a flame.

How can one troubleshoot relays and contactors as mentioned in the script?

Troubleshooting guides for various relays and contactors are provided in the description section of the video, offering step-by-step instructions for diagnosing and resolving common issues.