Correctly Sizing a Capacitor I don't know how many times a technician has said that they installed a part based on what was on their service truck.  I have heard of technicians wasting money over-sizing contactors, cutting down air filters, and even using controlled substances to clear condensate drains!  Of course, these scenarios all get the job done, but I would argue the many reasons why not to do these.  The one thing that gets to me is when a technician doesn't verify they are installing the correct size dual run capacitor.  Believe it or not, there is a simple method to figuring the correct size capacitor, without waiting on hold for the distributor's guru.  Of course, you could use a multimeter that reads microfarads (uf), but this will only tell you if the existing capacitor is weak - not the correct size! Testing Volts / Amps With the condensing unit operating under a load, you will need to measure the total volts between the HERM and COMMON terminals on the run capacitor (i.e. 345 VAC). 

Next, measure the amperage on the wire leading from HERM to START on the Compressor (i.e. 4 amps). Use the equation below to verify the size of the capacitor. The resulting microfarad (uf) should match the size of the installed capacitor. An over or under-sized capacitor will cause an imbalance in the magnetic field of the motor.  This hesitation when operating will cause noisy operation, an increase in power consumption, a drop in motor performance and eventually overheating or overloading motors like compressors.  best portable ac heater unitsThe run capacitor should have the exact microfarad (uf) that the motor is rated for.  air conditioning units for domestic useCapacitors rated above 70uf are considered Start Capacitors and are generally removed from the circuit electrically during operation.  how to maintain hvac unit

This is where the rule of +/- 10% of the rating came from, for Start Capacitors ONLY!  The voltage rating should be no less than the listed amount for the motor, for central heat pumps and air-conditioners this is usually a minimum of 370VAC.  Most new condensing units are specified for 440VAC capacitors, and are more durable during fluctuations in power supply.  I have seen some universal type dual run capacitors rated for as much as 700VAC, as this voltage rating does not impact uf performance.  The changes in uf will impact amperage draw and reflect on kilowatt hour usage though. When completing your early season maintenance this year for your customers, do them a service by testing capacitors and verifying their size.  You could just increase your service ticket total and save some all important power.  You may even prevent a call-back during the next heat wave! 0 members like this < Previous Post Next Post >How to Check an Air Conditioner Capacitor with a Multimeter

Capacitors are electrical devices, used in the compressors and fan motors of air conditioners, that store an electric charge. There are two common types used in HVAC units: The run capacitor, used in compressors and fan motors, maintain voltage supply leading to them and can increase torque when the device is started up. A start capacitor is used to provide extra torque to the compressor when a device starts up. Check either capacitor with a multimeter to see if they need to be replaced. Shut off all power to the air conditioner. Turn the air conditioner thermostat to the "off" position. Locate the breaker inside the breaker box that goes to the air conditioner and turn off the power there as well. Discharge the capacitor by running the metal tip of your screwdriver between the two terminals to rid the capacitor of any electrical charge. There may be a spark when this happens. Disconnect the wires to the capacitor using your needle nose pliers. Grip the wires with the pliers, pull them off the capacitor and place them to the side.

Prepare your multimeter by placing the leads into the terminals to test for resistance. Place the black lead in the hole marked "com," and the red lead into the hole that says "cap" by it. Set your multimeter to read Ohms, or resistance, on the highest setting your style meter has. This is done by turning the dial on the multimeter to the setting labeled "cap" or that has the Ohms icon on it. Place one lead on each of the capacitor's terminals and see what reading you get. This reading should be within 6 percent of your particular capacitor's rating. If it is not, then your capacitor is faulty and must be replaced with a new one. If your capacitor is leaking oil or is bulging out, then it needs replacement. There is no need to even test it. HVAC For Beginners: Capacitor Testing OhmCheck: How to Test Capacitor How to Check A/C Compressor Motor & Starter Capacitor How to Test an Air Compressor Motor Capacitor How to Check a HVAC Capacitor What Causes a Capacitor to Go Bad in an A/C Unit?

How to Wire Up a Start Capacitor How to Test Fan Motor Starting CapacitorsRun capacitors work with the motor on your air conditioning unit or furnace. They are designed to maintain a consistent electrical charge, which allows your furnace and AC motors to operate smoothly by creating a rotating magnetic field while the motor is running. This magnetic field provides the motor with a consistent voltage supply and increases the motor's torque at start up. There are two different types of run capacitors on the market -- dual run and single run capacitors. The difference between a single run capacitor and a dual run capacitor is the casing and the number of connecting terminals. Basically, a dual run capacitor is two single run capacitors held together in a more compact case. Also, single run capacitors have two connecting terminals, while dual run capacitors have three terminals -- one of them being the common terminal of the two capacitors packaged together. A bad run capacitor makes the appliance's motor run hot, and increases the amount of power that it consumes.

Therefore, you should periodically test the run capacitor on your air conditioner or furnace each time the appliance is inspected to ensure that it's performing well. This way, the motor will last longer and you'll save money on your utility bills. Digital or analog multimeter Follow the steps below in order to test a run capacitor: Preparing the Run Capacitor Flip the main breaker running to the furnace, air conditioner, or heat pump that you're working with to the Off position. Touch the metal part of your pliers to each of the terminals on the run capacitor, individually, to short them. This kills the charge on the run capacitor so that you can disconnect it safely. Even if the run capacitor that you're testing wasn't connected, you should still use a pair of pliers to short the terminals, because high-value capacitors can build up a residual charge. Conduct a visual inspection of the run capacitor. If it has physical defects, such as dents in the casing, chances are the run capacitor is bad.

However, you should still test the run capacitor to be sure. If the run capacitor is leaking, there is no need to test it, because it will need to be completely replaced. Using an Analog Multimeter to Test the Run Capacitor Switch the analog multimeter to the 1000 ohm (1 KOhm) scale. Connect the two testing wires on the multimeter to the terminals on the run capacitor. If your run capacitor is a dual run capacitor, connect the testing wires to the H and F connections, not the common connection. Look at the meter on your analog multimeter. If the hand goes up, stays there for a moment, and then goes down slowly, the run capacitor is good. If the hand doesn't move at all, or goes up, but does not go down, the run capacitor is bad and needs to be replaced. Using a Digital Multimeter to Test the Run Capacitor Switch your digital multimeter to the 1 Mega Ohm scale. Connect the testing wires on your multimeter to the run capacitor's terminals. If you have a dual run capacitor, connect the test wires to the F and H terminals, not the common connection terminal.

Look at the digital display screen to see if the numbers slowly continue to increase. If nothing happens or the reading that you get is more than six percent lower than the rating on the casing of your run capacitor, the run capacitor is bad and needs to be replaced. As long as you have the right tools, testing a run capacitor is simple. Because the process doesn't take long, you can easily test the run capacitors on your AC and your furnace every time you change the filters to ensure it's working properly. How to Test a Start Capacitor Image How to Test a Start Capacitor How to Check an AC Capacitor Image How to Check an AC Capacitor Picking the Right Capacitor Assortment for RF Projects Image Picking the Right Capacitor Assortment for RF Projects How to Connect a Capacitor to an Amp Image How to Connect a Capacitor to an Amp Dual Run Capacitor 45/5 MFD uf 370 440 v vac volts AC Motor HVAC 45/5 uf Image Dual Run Capacitor 45/5 MFD uf 370 440 v vac volts AC Motor HVAC 45/5 uf

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