The main function of a capacitor in an HVAC system is to provide the additional torque needed to get a unit running and the electricity needed to keep it running. There are different types of capacitors and you will find different types in different HVAC systems. As in the video, let’s begin by explaining start capacitors:
Start capacitors can be seen in outdoor units such as air conditioners and heat pumps, and are in addition to a dual run capacitor, which we will cover later. Generally only high-end factory models come with a start capacitor, but start capacitors or super boost capacitors can be installed in older or smaller units in order to increase torque and quicken start up.
The purpose of a start capacitor is to get the compressor up and running as fast as possible. As the compressor begins running, the potential relay will disconnect the capacitor from the electrical circuit. The two parts go hand-in-hand and it is a good idea to purchase them together.
A super boost capacitor is another type of start capacitor that has a potential relay built into it. This capacitor is very easy to install. It has two interchangeable wires – one that connects to the common terminal and one that connects to the HERM terminal. It can easily be stacked next to the run capacitor in your unit. If you have any additional questions about installation, please feel free to contact us. We are here to help.
We can also help identify the size and ratings of your capacitor so that you can replace it correctly. It is common for the label to become rusty and hard to read. As long as you know your unit’s model and serial numbers we can find the right capacitor.
Dual Run Capacitor
Dual run capacitors are also found on outdoor AC units and heat pumps and come in a variety of shapes and sizes. They are able to support two motors – the compressor motor and the fan motor. The dual run capacitor runs continuously while your unit is running. It has three terminals: HERM connects to the compressor, fan connects to the fan motor and common connects to the contactor. It is imperative to connect each wire to the appropriate terminal.
Again, it is important to read your data sticker in order to purchase the correct size of capacitor. The data that you should be looking for are the microfarads and the VAC, or voltage amp current. The capacitor in the video shows a capacitor with 45 + 10 microfarads. This means that 45 microfarads will go to the compressor and 10 microfarads will go to the fan motor. The new capacitor that you purchase must have the same amount of microfarads. VAC, however, is slightly different. If you are replacing a 370 VAC, you may replace it with a 440 VAC, but you cannot replace a 440 VAC with a 370 VAC.
Single Run Capacitor
Single run capacitors are generally used in furnaces. They have two terminals, HERM and common. The two wires that come from the furnace’s blower motor can connect to either terminal.
Over time, single run capacitors can get weak and you will begin having problems keeping your furnace running. If your fan motor is making a humming sound, this is a sign that you need a new capacitor. Note, it is dangerous to use your hand to give your blower motor a push. Please refrain from doing so.
Two additional safety tips for replacing your capacitor are:
- Make sure the power to the unit is off, both at the unit and at the circuit breaker.
- Deactivate the electrical charge, by using an insulated screwdriver and touching each terminal. It is also a good idea to wear insulated gloves.
Thank you for watching (and reading) our video. Until next time, stay warm!
A capacitor is used in most HVAC systems, including furnaces. It has two main functions – it provides the additional torque needed for starting a unit and gives the unit the electricity needed to keep it running. They are on continuous duty while the motor is running.
Capacitors provide a steady supply of electricity to the fan motors and help the blowers move hot air through your system. In other words a capacitor is similar to a battery, storing electricity and stabilizing currents.
Without a capacitor your furnace’s motor will not start and the unit will not run. In fact, if the motor in your furnace won’t start, the capacitor is likely the problem.
Capacitors are categorized by microfarads and voltage. Microfarads are what measure the capacitors ability to store an electrical charge. A capacitor will range from 1.5 to 100 microfarads and will be classified at either 370 VAC or 440 VAC.