Your central heating system is fueled by refrigerant and distributed via a blower motor. The blower motor requires an electrical boost to power up and a steady background boost while operating. Those boosts are provided by the start and run capacitors, respectively.
Has your furnace's blower motor started experiencing intermittent outages or otherwise seem to be malfunctioning? Your capacitors could be failing or nonfunctional. Testing the capacitors is doable if you have a multi-meter and some experience working with electricity. Otherwise, you will want to call in a furnace repair person to perform the tests.
There are a few tips that can make the capacitor testing process easier and safer. Make sure you turn off all power to the furnace before attempting any repairs.
Find and Use Your Owner's Manual
No general online guide can provide the specific location of your unit's capacitors and any access details you might need. You will need to keep a copy of your owner's manual handy to help find the capacitors.
Didn't save your owner's manual? Write down the make and model of your furnace and go online. Search for the make, model, and the words "owner's manual" and you should find a copy available to read or print. Can't find your unit online? Contact the manufacturer for assistance or call in an HVAC tech to perform the testing.
Always Discharge the Capacitors Using a Multi-Meter
When you turn off the main electricity to the furnace, most of the furnace's parts are now safe to handle without worrying about electrocution or blown fuses. However, capacitors are designed to hold and electrical charge over a long period of time, which means there is still an electrical charge in the wires attached.
Make the testing process safe for yourself by discharging the capacitors. The discharging process involves carefully removing the attached wires with insulated wires, which will prevent the current from traveling up regular metal pliers and into you. You can then attach the ends of the multi-meter to the capacitor's connection points, set the meter to the AC setting, and then wait for the reading to drop down to zero.
Read the Capacitors for the Healthy Range
There are two ways that your capacitor and your chosen multi-meter can make the testing process very easy on you. First, look at the sides of the capacitor for percentage numbers attached to a unit called mfds, or macrofarads. The percentages are the healthy range of mfds for your capacitor.
How do you know how many mfds are currently in the capacitor? You can switch your multi-meter setting over to capacitor testing and the meter will automatically check for that unit and display a percentage number you can compare to the capacitor. Contact a company, such as Maryland Oil Company, for more information.