Ohmmeter Does 3 Vital Tests
You can test and trouble-shoot electrical appliances like a pro--safely and easily--using an ohmmeter.
An ohmmeter can test virtually every single electrical component in any appliance--small and major. This includes all power cords, switches, solenoids, relays, timers, thermostats and heating elements, to name just a few.
By simply placing the meter’s probes on the component’s wires or terminals, you can determine quickly and safely if the part is defective.
Some of the typical tests that you can perform include checking the water-level switch on a clothes washer, testing a thermostat of a refrigerator or freezer and checking the heating element of a clothes dryer, electric range or oven.
The owner’s manual, which comes with each meter, provides more specific examples and instructions.
And, if you’re concerned about receiving an electrical shock, don’t be. When using an ohmmeter, double check to make sure the appliance is unplugged from the electrical outlet.
An ohmmeter can perform three vital electrical tests. One is to determine if a continuous, unbroken circuit exists. Another test measures the resistance to the flow of the current. Every electrical component has a specified amount of resistance that is measured in ohms.
Testing tells you if the component meets the original requirements set for it.
Ohmmeters also can test for short circuits that make components inoperable.
When the needle of the meter points to the symbol for infinity, the meter isn’t capable of measuring the resistance of the tested part. Therefore, an open circuit exists and you need a new part.
When testing for continuity, you aren’t seeking an exact numerical value. A circuit is either open or it isn’t. If it’s open, the needle will point to infinity. If the circuit isn’t open, the needle will point to a number.
The appliance’s switch needs to be turned on when testing for continuity or resistance.
If the switch is left off, it will cause the needle to point to infinity, indicating that there’s an open circuit, which may not be the case. If the appliance has two switches, such as a toaster-oven, be sure both are switched on.
Most ohmmeters have a range-selector with three RX positions--RX1, RX10 and RX100. Other meters have RX1000 (often designated RX1K) and RX10000 (RX10K) settings for reading greater ohm values.
To determine the resistance of a circuit or component, multiply the RX value by the number that the needle points to.
For example, if the range selector is set on RX1 and the needle points to 50, then the circuit has a resistance of 50 ohms. If the range selector was set at RX10, the circuit would have a resistance of 500 ohms.
When testing for continuity, start with the range selector at RX1. If the needle points to infinity, switch the selector to RX10 and then RX100. If the needle doesn’t move off the infinity mark, an open circuit exists.
Often when checking the resistance value (ohms) with the meter set at RX1, you’ll get a reading on the high end of the scale.
Because the high end isn’t calibrated very precisely, switch the selector to RX10 and bring the needle into the lower, more precisely calibrated end of the scale.
The exact resistance values of the parts of an appliance are printed on a wiring diagram glued to the appliance. Appliance manufacturers can also provide resistance values for specific parts.
Another alternative is to check the resistance values listed in repair books. The reading that you get doesn’t have to equal exactly what is listed in the book.
For example, a repair book lists the resistance value of an electric range cooking element at 50 ohms. If you get a reading of 45 ohms, that’s close enough. A much lower reading of 10 ohms would indicate that a short exists in the element. When a short exists, the meter will display a low value--it won’t point to infinity.
