Table 4-2. Unit Troubleshooting Guide (Continued)
TEST OR INSPECTION
Relay contacts can be thought of as stop or go signs and switches can be thought of as change
direction signs or stop and go signs.
The ROWPU schematic is shown with no power on the circuits and the system shutdown with no
pressure in any of the hydraulic or air systems. This means that if you were to check any switch or
contact, without power or pressure to the unit, it must match what the schematic shows. Selector
switches must be moved to the position shown by the arrow to indicate properly.
Relay contacts are either open (two vertical lines) or closed (two vertical lines with a diagonal
across them). When a relay coil is energized it switches all its contacts to the opposite position;
closed to open and open to closed. When the power is removed the contacts switch back to their
normal positions. The relays can be thought of as the traffic controllers in the electrical circuits.
Dashed lines between switch contacts mean each contact is on that switch operator. A switch
contact which has a symbol like OXO next to it means the contact is open when the switch lever is
to the left, closed when the lever is in the center and open when the lever points to the right.
Lines which cross but do not have a black circle where they cross are not connected.
Each relay contact will have shown two numbers, such as A3X and A3Y. This refers to where the
contact is located on the relay controlling it. The A means first bank (closest to the sub-panel, B
means second or middle bank, and C means outer or third bank). The 3 is the left to right
designation and X is top of relay, Y is bottom of relay. Some relays only have an A bank or an A
and B bank but the reference always follows that shown on the drawing.
The left side, or hot line, on the ROWPU schematic list line numbers (do not confuse them with
wire numbers) of each horizontal or control line in the circuit. On the right, or neutral side, is a brief
description of each lines function in the circuit.
When troubleshooting the control panel with no power on the system, relay contacts and starter
contacts can be manually switched to the energized condition by pushing in on the square
button on relays and the starter contact back on starters. Releasing them returns the contacts to
their unpowered condition. This is useful when checking continuity on a control circuit line.
Remove wires from motor leads or relay coil contacts to determine if a motor or coil has a
Step 2. ELECTRICAL FAULT ISOLATION. It is important when troubleshooting to pinpoint the problem accu-
rately, repair it, and return the system to operational readiness as rapidly as possible. There are several
steps that can be taken to help speed up the process of troubleshooting.
The majority of problems will have causes external to the control panel. Water, dirt, chemicals and
abuse to components and cables will be the source of most problems. By comparison, the
components in the control panel are in a clean environment and are capable of many thousands of
cycles before breaking or burning out, and have been proven to work in the proper way. The
exception to this are any components with motors such as timers or hourmeters. Keeping the
above in mind, all troubleshooting should initially assume the control panel is not the cause of the
Use the reference guide and set up the control panel switches for operation yourself. Never
assume that somebody else has done it correctly.
Talk to the operator and try to determine as accurately as possible what really happened so as to
eliminate needless troubleshooting time.
Try to do batch troubleshooting whenever possible. This means instead of starting at the hot line
and working through a circuit step by step you should start at the hot line and check it halfway, or
whatever is possible, through the circuit first. This allows you to eliminate several components in
one step, or conversely, pin the problem to the present check points.
Be sure to use the Iight test to determine that bulbs are not burned out Ieading to improper
Be sure all circuit breakers are on before attempting to diagnose a problem.