Ohm’s Law describes the relationship between volts, current, and resistance.
E = electromotive force (volts)
I = current (amperes)
R = resistance (ohms)
Here is a common figure and some formulas to help you think about volts, current, and resistance.
E = I x R
Mechanical failure — Excessive vibration and wear and tear can cause the mechanical part of a device to break down.
Open circuit — A break or “open” in the circuit where current will not flow.
Short circuit — Occurs when current takes a direct path across its source. Signs of a short circuit are increased amperage, decreased resistance, and decreased voltage.
Ground — Occurs when current takes an incorrect path in a circuit due to insulation breakdown, or pinched or misplaced wiring. Signs of a grounded circuit are abnormal voltage, resistance, and amperage.
Pictorial diagrams — Reference the actual physical location of components and wiring.
Schematic diagrams — Illustrate a current path through the system. (See Figure 1.)
Sequence of operations — Manufacturers often include this information with their equipment. It tells you, in sequential order, how the system operates. This supplements pictorial and schematic wiring diagrams when trying to determine if voltage should be present at a certain time and location in the system.
Your senses — Your sense of smell can aid in detecting burnt, electrical components. Your sense of sight can pinpoint broken wires and loose connections. Your sense of hearing helps to identify when equipment is not running normally. Due to safety reasons, however, the sense of touch should not be used in electrical troubleshooting procedures.
Working knowledge of how the system is supposed to operate — Sometimes, wiring diagrams and sequence of operation materials are not available. This is when you rely on your working knowledge and experience. To build that knowledge base, pay attention as you carry out your daily assignments. Make notes for future reference.
Flow charts — Troubleshooting flow charts are available for many systems and components you will encounter.
Electrical test instrumentation (ETI) — Rely on your ETI; it can be your best friend in the field. By using the correct instrument for the situation at hand, you will see what is happening within the circuit or components you are testing.
Your frame of mind is key. Enter the troubleshooting zone. Allow a calmness to surround you. Focus. Your preparation reinforces a powerful resolve, a resolve to succeed and locate the source problem.
Communication is essential. Listen carefully to the person reporting the problem. Keep the nature of the complaint in mind as you carry out your procedures.
Power first. After power has been established at the equipment, work through the sequence of operation until the faulty circuit has been located. Systematically go through the circuit until you have discovered the fault.
Rothacker is a director for area51hvac.com. For questions or comments on the Tech Page, contact Rothacker at firstname.lastname@example.org (e-mail).
Publication date: 03/18/2002