How to measure the capacitance with standard run and dual run capacitors.
Capacitors are simple devices used in most HVAC equipment to assist compressors and motors with starting and running effectively. During the hot summer months the capacitor in the outdoor units failed at a high frequency rate. Changing them is a fairly simple process, but first you need to understand what is a capacitor.
A capacitor is a device that stores electricity. The amount of storage capacity is measured in Farads.
Capacitors come in all shape and sizes, but have the same function. The shape of the capacitor in HVAC equipment is usually dictacted on how it is mounted in the equipment. Can you use a oval run capacitor with the same rating as a round run capacitor? The answer is yes to this example and to many others. Another question is "What is a dual run capacitor?" The dual run capacitor is nothing more than 2 run capacitors in one housing. It will have two MFD/uf ratings such as... 5uf/40uf and can be found in a heat pump or air conditioning unit. The 5uf is for condenser fan motor and the 40uf is for the compressor.
A failed or failing capacitor can cause motors and compressors not to run at all or they can try to start and make a humming sound repeatably. Motors can run slow and sometimes overheat and shut off only to cool down and start again.
Verify the capacitors prior to each heating and cooling season with a multimeter that can measure capacitance. The rule of thumb is to change the capacitor if the capacitance drops below 10% of the original value.
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SAFETY NOTE - ALWAYS TURN THE MAIN POWER AND GAS VALVE OFF BEFORE SERVICING ANY HVAC EQUIPMENT. SERIOUS INJURY CAN OCCUR.
This guide's intention is to provide an understanding of the operation of a furnace. It is not intended as a hands-on teaching tool, or aide. All HVAC equipment should be serviced by a licensed HVAC technician. Consult your local, town, city, and state laws, ordinances, and regulations prior to accessing, engaging, troubleshooting, repairing, or servicing any HVAC equipment.