How to test an electric motor capacitor: this article gives a description of electric motor capacitor test procedures to determine if a capacitor is damaged or working normally & test procedures to measure the capacitor's capacitance or microfarads, MFD, or uF to determine if it is working within its rated capacitance range. This article series gives electric motor start-run capacitor and hard-start capacitor installation instructions to get a hard-starting air conditioner compressor motor, fan motor, refrigerator, or freezer compressor or other electric motor (such as a well pump) going. If an electric motor that uses a starting or run capacitor won't run try replacing the capacitor. If the electric motor runs, check the current draw (AMPS) on both of the capacitor leads. You should see current draw on both leads. If not the capacitor is probably failed. There are two quick indicators of a bad electric motor start capacitor: Use a VOM in ohms setting to check resistance across the capacitor.

If the meter does not move (no current flows) the capacitor is "open". If there is zero resistance the capacitor is shorted. In the partial wiring diagram at left, the compressor (COMP) is at lower right, and the component labeled SC shows the position of the starting capacitor in the air conditioning equipment's wiring schematic. Watch out: while you might get lucky by finding that just replacing the starter capacitor fixes an air conditioner compressor, a fan motor, or another electrical motor, a hard-starting motor can be an indication that the more expensive A/C compressor or electrical motor is itself beginning to fail. A starting capacitor has the single job of giving a very large voltage boost to a motor to start it spinning. It does not keep at the job once the motor is operating. The rating on a starting capacitor will include a high MFD number and the operating voltage range. Temperature ranges and other data may also be provided on all caps. A run capacitor has the job of keeping an electric motor spinning.

The rating on a run cap will include the MFD rating and voltage range. Dual run capacitors combine two different capacitor ratings and provide run support for two different motors. In a common air conditioning application these would be the compressor (marked Herm), and the compressor/condenser unit fan (marked F or Fan). The rating on a dual run cap will include two MFD ratings and a voltage range, such as 45/5/440 which translates ashome air conditioner compressor installation A standard digital VOM or multimeter that includes a MFD (microfarad) option is set (on its dial or selector) to MFD and with the capacitor disconnected from any other wiring the VOM probes are touched to two terminals on the capacitor.how much does a compressor for a ac unit cost If the uf/mfd reading on the meter is close to the rating stamped on the capacitor label then the device is in normal condition. flushing out ac unit

For example on a 45MFD (or uf) capacitor your meter should read close to 45. Watch out: do not attempt to touch or measure equipment with power on and wires in place. You could be injured or killed or could cause a fire or explosion. Watch out that capacitors can store energy and deliver a shock even after power has been turned off. See DMMs VOMs SAFE USE OF. Example: testing a blower fan motor winding: referring to the electrical diagram for your equipment, unplug electrical connectors at the fan motor. Measure the resistance between each lead wire with a multimeter or VOM. The multimeter should be set in the X1 range. For accuracy, don't measure when the fan motor is hot, allow it to cool off. When the resistance between each lead wire are those listed in the specifications for your equipment the fan motor should be normal. Zero resistance or infinite resistance are indicators of a problem. More examples of checking wiring: See HARD STARTING COMPRESSOR MOTORS