Capacitors are devices capable of storing electrical voltage and are used in electronic circuits, such as those found in motors and compressors in cooling or heating systems. There are two main types: electrolytic (which use a vacuum tube and transistor) and non-electrolytic ones which are used to regulate direct overvoltages. The former may be malfunctioning because they discharge too much voltage or because they run out of the electrolyte and are therefore unable to maintain a charge; the latter, on the other hand, are more prone to voltage losses. There are several methods for testing a capacitor to see if it still works as it should.
Steps
Method 1 of 5: Using a Digital Multimeter with Capacity Setting
Step 1. Disconnect the capacitor from the circuit it belongs to
Step 2. Read the nominal value of the capacitance which is printed on the body of the element itself
The unit of measurement is the farad, which is abbreviated with the capital letter "F". You might also find the Greek letter "mu" (µ) that looks like a lowercase "u" with a longer "leg" at the beginning. Since the farad is a very large unit, the capacitance of almost all capacitors is measured in microfarads, which is equivalent to one millionth of a farad.
Step 3. Set up the multimeter to measure capacitance
Step 4. Connect the probes to the capacitor terminals
Join the positive (red) pole to the anode of the element and the negative (black) pole to the cathode; on most capacitors, especially electrolytic ones, the anode is clearly longer than the cathode.
Step 5. Check the result on the multimeter's display
If the value is similar or close to the nominal value, the capacitor is in good condition; if there is less or no number, the item is "dead".
Method 2 of 5: Using a Digital Multimeter with No Capacity Setting
Step 1. Disconnect the capacitor from its circuit
Step 2. Set up the multimeter to detect resistance
This mode is indicated by the word "OHM" (the unit of measurement of resistance) or the Greek letter omega (Ω), the symbol of the ohm.
If your test tool has an adjustable resistance range, set the resistance range to at least 1000 ohms
Step 3. Connect the multimeter's probes to the capacitor terminals
Again, remember to connect the positive (longer) lead to the red probe and the negative (shorter) lead to the black probe.
Step 4. Make a note of the multimeter reading
If you wish, you can write the starting value of the resistance; the data indicated by the instrument should quickly return to the number present before connecting the probes.
Step 5. Unplug and connect the capacitor several times
You should always find the same result, in which case you can conclude that the element is working.
If, on the other hand, the resistance does not change during one of the tests, the capacitor is not working
Method 3 of 5: Using an Analog Multimeter
Step 1. Disconnect the capacitor from its circuit
Step 2. Set the multimeter to detect resistance
Just like with analogue instruments, this mode is indicated by the word "OHM" or by the omega symbol (Ω).
Step 3. Connect the instrument probes to the capacitor terminals
Connect the red one to the positive (longer) terminal and the black one to the negative (shorter) terminal.
Step 4. Look at the results
An analog multimeter uses a needle that moves along a graduated scale to show data; the behavior of the needle allows to understand if the capacitor is working or not.
- If it shows little resistance at first, but then gradually moves to the right, the capacitor is in good condition.
- If the needle indicates low resistance and is not moving, the capacitor has suffered a short circuit and you need to change it.
- If no resistance is detected and the needle does not move or indicates a high value and remains stationary, the capacitor is open and therefore "dead".
Method 4 of 5: Using a Voltmeter
Step 1. Disconnect the capacitor from its circuit
If you wish, you can disconnect only one of the two terminals.
Step 2. Check the rated voltage of the element
This information should be printed on the outer body of the capacitor itself; look for a number followed by the letter "V", the symbol for volt.
Step 3. Charge the capacitor with a known voltage lower than, but close to, rated voltage
For example, if you have a 25V element, you can use a 9V voltage; if you are dealing with a 600 V element, you should use a minimum potential difference of 400 V. Wait for the capacitor to charge for a few seconds and check that you have connected the positive (red) and negative (black) leads of the source of energy to the respective terminals of the component.
The greater the difference between the rated voltage value and the one you are using to charge the capacitor, the more time you need. Generally speaking, the higher the voltage of the power source you have, the higher the nominal one you can test without difficulty
Step 4. Set the voltmeter to read the DC voltage if the meter can be used with both DC and AC current
Step 5. Connect the probes to the capacitor
Join the positive (red) and negative (black) ones to the respective ends of the capacitor (the negative terminal is shorter).
Step 6. Note the initial voltage value
It should be close to the current you fed the capacitor with; if not, the component is malfunctioning.
The capacitor discharges its potential difference in the voltmeter; consequently, the reading tends to zero as you leave the probes connected. This is a completely normal effect, you should only worry if the initial reading is much lower than expected
Method 5 of 5: Shorting the Capacitor Terminals
Step 1. Disconnect the capacitor from the circuit
Step 2. Connect the probes to the terminals
Remember to respect the agreement between the positive and negative terminals.
Step 3. Connect the clothes to a power source for a short time
You shouldn't be in contact for more than 1-4 seconds.
Step 4. Detach the garments from the power source
In this way, you do not damage the capacitor when you proceed with the work and reduce the risk of getting a strong electric shock.
Step 5. Short-circuit the capacitor
Wear insulated gloves and do not touch any metal objects with your hands as you go.
Step 6. Observe the spark that forms
This detail provides information on the capacitance of the capacitor.
- This method only works with capacitors that have enough energy to produce a spark when short-circuited.
- However, this technique is not recommended because it can only be used to understand if the capacitor holds the charge and is able or not to emit sparks when connected in short circuit; it does not allow to know if the capacity is within the nominal values.
- Following this method on large capacitors could cause serious injury and even death.
Advice
- Non-electrolytic capacitors are typically not polarized; when you test them, you can connect the probes of the voltmeter, multimeter or power source to both ends.
- Non-electrolytic capacitors are divided according to the material they are made of - ceramic, plastic, paper or mica - and plastic ones are subject to further classification based on the type of plastic.
- Those found in heating and cooling systems are divided into two types based on function. The power factor correction capacitors keep the electrical voltage that reaches the fans and compressor motors of boilers, air conditioning systems and heat pumps constant. Starters are used in units with high torque motors, such as some heat pumps or air conditioning systems, to provide the extra energy needed to run them.
- Electrolytic capacitors typically exhibit a tolerance of 20%; this means that a fully functional element could have a capacity 20% greater or less than the nominal one.
- Remember not to touch the capacitor when it is charged, you will get a very strong shock.
