Failing HVAC Parts - Capacitors
This will be my first article on a series of HVAC parts that commonly need replacement. HVAC systems are machines with electronic controls similar to many other machines. They have capacitors which is an electrical component that stores charges to be let out at once. A common use for external air handlers is spinning up the compressor or blower motor. These devices need a lot of energy to start compared to maintaining speed once they are going. So the capacitor stores energy to be released when the device needs a big boost. Just like any other part, capacitors can burn out.
Capacitor use in common Denver HVAC applications can be divided into run capacitors and start capacitor. The motor starter capacitor adds torque to the motor to get it to speed. These are used in simpler single phase motors. However these simple HVAC units are the most common ones you will find powering your Denver furnace or air conditioner. The start motors are usually for the compressor, interestingly a commonly replaced Denver HVAC part. As the world turns to higher efficiency air handlers and overall systems, many motors use capacitors to increase run efficiency. These motors are used in all kinds of applications like fans, furnace blowers, condenser motors and chilled water pumps. Those with electrical knowledge will want to know that most shut-offs for capacitor use use a potential relay after the motor is spun up.
Capacitors work as a kind of giant battery. Two metal plates are suspended between an insulator that prevents the electrons from jumping plates. Capacitors are much more dangerous than batteries however because they have the ability to empty their charge all at once. Therefor workers must be extremely careful when handling any capacitors. Always try and determine if it maintains a charge and use gloves either way. Use a resistor to discharge the capacitor before working on any circuits it may be connected to. The electronics can still maintain power with the supply off.
Run capacitors are not as powerful as start capacitors. The power is measured both in volts and microfarads. It is always best to replace a capacitor with one of the exact same rating. You can always test to measure the capacitor rating on site vs the manufacturer's specifications. 10% is about the limit you can be safely off. Because these units do burn out with all the electricity to handle, checking the capacitor will always be on the checklist if a motor fails to start.
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