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Hi! In this article, we'll be talking about the basics of performing continuity checks using an ohmmeter (need one?). Grab your favorite drink and read on...
SAFETY NOTICE----SAFETY NOTICE----SAFETY NOTICE
ALWAYS DOUBLE CHECK TO MAKE SURE THE POWER IS DISCONNECTED FROM THE APPLIANCE BEFORE REMOVING ANY ACCESS PANELS OR COVERS!
hen tracking down the source of an electrical problem in an appliance, there are times when it will be obvious which component has failed. When a bake element in an electric range blows apart, for example, all it takes is a visual inspection to find the problem. There are situations, however, in which the problem is not so obvious, and it takes more than a quick look to find out what’s wrong. In some of these situations, you can use a test meter to check the resistance or continuity of an electrical component, such as bake element, switch, or motor. In order to accomplish these test procedures safely and correctly, there are some basic things you need to know.
Types Of Meters
here are two basic types of test meters, identified as Analog and Digital. Analog meters have been around for many, many years, and there is a wide variety of styles and models. The best way to think about an Analog meter is that it is the type of meter that uses a needle pointing to a set of numbers on a scale to provide information.
n the illustrations above, we're showing a couple of examples in which you can use an Analog meter, and we’re also showing one of the basic concepts that you need to understand about this type of meter... that it doesn't read from left to right, but from right to left. Zero on an Analog meter is at the farthest right of the scale.
ou'll notice that the instruction in our illustration states that "a good fuse will read close to 0" and that our drawing shows the needle almost all the way to the right. That’s because, as we said, the numbers on the face of an Analog meter aren’t shown from left to right, but from right to left.
ou’ll also note that there are two types of fuses shown in our illustration, a screw-type and a cartridge type. In addition to circuit breakers that protect the electrical system in your home, some individual appliances may also be wired to a cartridge or screw-type fused disconnect box, such as an electric dryer in an older home. If that’s the case, then you can remove these fuses and check them with a meter to see if they are blown, or if they are OK.
NEVER ATTEMPT TO REMOVE A FUSE FROM A CIRCUIT UNLESS YOU ARE SURE THE POWER TO THAT CIRCUIT IS TURNED OFF EITHER BY SWITCHING OFF A CIRCUIT BREAKER IN THE MAIN PANEL OR BY REMOVING A FUSE HOLDER FROM THE MAIN CIRCUIT PANEL!
ther situations in which you may use a meter to check a fuse is in the case where an appliance has a fuse within it. For example, in some cases, gas ranges may have a fuse that protects the glow coil ignition system, and in some situations, appliances that use an electronic control board may have a fuse that snaps into a holder on the electronic control assembly. In most of these cases, you can’t tell if a fuse is OK by looking at it, which means you have to use a meter to test the fuse for continuity (which means it’s OK), or to find out if it’s open (which means it’s blown). If a fuse is blown, an Analog meter will show what’s known as Infinity (meaning open, or to put it simply…the needle doesn’t move). If the fuse is OK, an Analog meter will show close to 0 on the scale, providing you have chosen the proper resistance measurement scale and made sure the needle points to 0 when the two leads of the meter are touched together, as we’re showing below.
s this illustration shows, the steps to remember about using an Analog meter to check continuity of a switch or fuse, or the resistance of an electrical component that does work (such as a bake element, washing machine water valve solenoid, or motor) you need to:
: Set the meter range knob to the Rx1 scale.
: Make sure the two leads of the meter are touching. Be sure they’re making good contact.
: Turn the Ohm Adjustment Knob so the needle points to 0.
nce you've completed the above steps, you’re ready to use an Analog meter to test either fuses, switches, or electrical components that have a relatively low resistance…things like bake and broil elements, clothes dryer motors, washing machine motors, dishwasher or washing machine water valve solenoid coils... any electrical component that will have a resistance from 1 to 100 Ohms.
Continuity & Resistance Defined
ontinuity is the electrical term used when describing a switch or set of contact points that, when closed, will allow electricity to pass through without resistance. We also use the term continuity when describing a good fuse because it, like a switch or a set of contact points, will allow the unrestricted flow of electricity.
esistance, on the other hand, is the electrical term used when describing the resistance of a load... something that does electrical work when energy is applied to it. A light bulb is the simplest illustration of a load. When 120 volts is applied to a light bulb, we get light. When electricity is applied to a bake element, we get heat. When electricity is applied to a motor, we get mechanical energy.
o, while a switch or set of contact points inside a switch is supposed to have a little resistance as possible (very close to zero... a fraction of an Ohm), a load (something that does work, producing light, heat or mechanical energy) is supposed to have some level of resistance.
n the example above, the electrical component being tested has a resistance of 2 Ohms. With our Analog meter Range Selector knob set on the Rx1 scale, and with our Zero adjustment accomplished before going ahead with testing the component by touching the leads to the electrical connections of that component, the needle will only rise from the Infinity reading (way over at the left of the scale... the number 8 laying on it’s side, the symbol for Infinity - "∞") to the number 2 because the component has a resistance of 2 Ohms.
f an Analog meter is being used to test a load that has a high resistance, the Range Selector knob can be set to a different "R" setting. For example, choosing the Rx100 scale, and touching the leads together and adjusting the knob to 0 before testing the component would allow you to read that higher resistance by using the same number 2 we used in the previous example. The difference is that with the Range Selector knob set on the Rx100 scale, the number 2 now represents 200 Ohms. With the knob set on the Rx1K (1,000) scale, the number 2 would represent 2,000 Ohms.
ll of which brings up the point that you have to have some knowledge of approximately how much resistance you’re supposed to be getting on a given component so you can set your Analog meter to the proper resistance scale. Often, the only way to get exact information on how much resistance a given component is supposed to have if it’s OK is from a manufacturer’s troubleshooting manual. However, there are some basic rules of thumb you can apply when testing electrical components with an ohmmeter.
: Always set an Analog meter on the Rx1 scale to test a switch or fuse.
: Bake elements and surface unit elements will have a relatively low resistance, so the Rx1 scale can be used to check them. If a meter shows Infinity when an element is tested, the element is open (broken) and needs replacing.
: Motor windings (washing machines and clothes dryer motors) also have a relatively low resistance, so the Rx1 scale works when checking them also. If a meter shows Infinity when a washing machine or dryer motor winding is checked, the winding is open (broken). If a meter shows a very high resistance, say in the 1,000’s when a motor winding is checked, the winding is shorted. In the case of an open or shorted winding, the motor needs to be replaced. Note: Some other types of motors, such as those used in icemakers, or in self-clean range locking systems are supposed to have a very high resistance, and a reading in the 1,000s doesn’t mean that they’re shorted.
: Water valve solenoids, such as those found on washing machine or dishwasher fill valves traditionally have a low resistance, so using the Rx1 scale on the Analog meter to check them will provide you with accurate information.
Digital meter is used to test switches and loads in much the same way as an Analog meter.
o understand the operation of the meter shown in the illustration above, we'll go by the numbers:
- This is the Function and Range Switch. Turning it will turn the meter on. For checking continuity or resistance, the pointer of the knob is set in the lower left quadrant where the Ohms symbol is, and for checking low levels of resistance, choose the 200 setting.
- This is where the Digital meter will display the information. If you were checking a bake element that is supposed to have 10 Ohms resistance, the number 10 will appear here if the element is OK. If when testing the element, the meter shows OL, it means that the element is open. In Digital meter speak, OL (Open Line or Overload, depending on the function the meter is being used for) means the same thing as Infinity in an Analog meter.
- This is the Common jack on the meter where you would insert the black meter lead.
- This is the Ohms jack on the meter. Insert the red meter lead here.
- This is an additional jack that you won’t be using when checking resistance or continuity.
ith the Digital meter we’re showing in our example, you have the option of choosing given resistance scale other than 200. These other scales would only be used if you were checking the resistance of components other than those we’ve mentioned. When using a Digital meter, there is no need to touch the leads together before making a continuity or resistance check. Unlike an Analog meter, Digital meters do not need to be calibrated in order to read accurately. Other than this difference, you can use a Digital meter to make the same checks we’ve described using an Analog meter as an example.
hen using either an Analog or Digital meter to check continuity or resistance of a component, there are two basic rules to keep in mind:
: Always disconnect the power supply before removing any access panels or electrical components for testing with an ohmmeter.
: Always disconnect the wiring connected to any component you’re testing. This is called isolating the component and prevents your meter from giving you a false reading because it may be sensing other components in your appliance.
omponents You Can Check With An Ohmmeter In Your Electric Range
- You can check your bake or broil elements for proper resistance.
- You can check surface unit elements for proper resistance.
- You can check a surface unit switch to see if the contact points inside the switch are working properly.
In a standard surface unit switch, there are two terminals that bring the power in, and they are labeled L1 and L2 (Line). There are two terminals that allow the power out, and they are labeled H1 and H2 (Heat)
To test a switch of this type, disconnect the power supply before removing the access panel, disconnect the wires from the switch (make sure you can remember where the wires are connected to….you can draw a simple picture to remind you). Attach one lead of the meter (be sure it is set on the proper scale and calibrated if necessary) on L1. Attach the other lead to H1. With the switch turned on and calling for heat, you should get a continuity reading between these two contact points. Next, place one lead of the meter on L2 and the other lead on H2. You should also get continuity with this test when the switch is in the on position.
- You can check the thermostat to make sure it’s closing and calling for heat when it’s set to a BAKE or BROIL position. In many cases, checking for continuity from the L1 terminal to the BAKE terminal and then from L1 to the BROIL terminal will show whether the contacts inside the switch are closing when the thermostat is turned on and calling for heat.
omponents You Can Check With An Ohmmeter On Your Electric Dryer
- You can check the heating element. With the power supply disconnected and the appropriate wiring disconnected from the heater connection terminals, check for resistance at the two heating element connections.
- You can check any disc-type operating thermostats, limit switches, or fuses for continuity (gas or electric dryers). With the power supply disconnected and the appropriate wiring disconnected, checking with an ohmmeter on the two terminals of these components will tell you if the contact points inside are open or closed. A fuse should always show continuity. A high limit switch should also show continuity. An operating thermostat should show continuity unless it’s very warm, and then it could show Infinity on your meter.
omponents You Can Check With An Ohmmeter On Your Washing Machine
- With the power supply disconnected and the appropriate wires disconnected, you can check the resistance of the fill valve solenoid coils.
- If you washing machine is equipped with a lid switch, you can disconnect the power supply, disconnect the appropriate wiring, and check to make sure the contact points inside the switch have continuity when the lid of the washing machine is down.
omponents You Can Check With An Ohmmeter On Your Dishwasher
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Using A Circuit Tester
- With the power supply disconnected and the appropriate wiring disconnected, you can check the resistance of the water inlet valve solenoid.
- With the power supply disconnected and the appropriate wiring disconnected, you can check to make sure the contact points inside the float switch have continuity while the float is down. You can also check to make sure there is Infinity between the contact points when the float is raised up.
f your 120-volt appliances are controlled by an electronic control system, the wall receptacle must be wired correctly. If not, you may experience erratic operation of your dishwasher, microwave oven or gas ranges. One way to check that your wall outlet is properly wired is to use a circuit tester.
his device is simple and safe to use when testing 120-volt circuits. All you have to do is plug it into the outlet and observe the pattern of lighting that shows up on the tester body. What you’re looking for is two yellow lights, which will show that your wall outlet is wired properly. In the event that you see any other pattern than two yellow lights, call an electrician to check and repair your wall outlet.
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