Using Jumper Wires as a Troubleshooting Tool

Jumper wires, when used correctly, are a great tool to help you troubleshoot HVAC equipment. But, when used incorrectly, they can damage the system you are trying to repair. Remember this one important rule - Never place a jumper wire across a load. Here's why: If your place your jumper wire across a switch, all you are doing is closing a circuit that the switch would normally close and allowing current to flow through the circuit. If you place your jumper wire across a load, you are creating a short circuit where one is not intended to be. You will blow a fuse, trip a circuit breaker, burn out a switch, burn wires, or a combination of all or some of the damage listed.

Here are a few other things to keep in mind when using jumper wires:

• The jumper wire should be the same gauge or larger than the circuit you are jumping out.
• Even if the alligator clips on the jumper are insulated, it is a good idea to turn off the power before you attach your jumper.
• Jumpering across a live circuit usually causes a spark when the alligator clips are connected. Be prepared.
• It is not a good idea to jumper out a high current circuit like a compressor or large horsepower motor.

Jumper wires are not to be used as your primary troubleshooting tool, use your voltmeter first.  Let's say you're working on a heat pump system, and using your voltmeter you find the low pressure cutout switch is open. You get out your jumper wires and bypass the low pressure switch. This allows you to further check the system operation and to help determine if the low pressure switch is faulty or if it was caused by an actual low pressure condition. If you don't do this and tell the customer they have a bad low pressure switch and charge them to replace it, it will be very hard to then tell them that the system is low on charge. Which was the original problem to begin with.

If you want to become an HVAC technician, you can learn more HVAC troubleshooting tips by signing up for our online HVAC Technician Course.

by Ron Walker