QUANTUM™ HD UNITY SYSTEM CONTROLLER
MAINTENANCE
090.670-M (APR 2020)
Page 59
If you encounter a problem that is not easily identifiable or
initially appears unexplainable, check the following:
• Is the panel powered by an isolating power source such
as a control transformer?
• Is the panel powered from a lighting or utility panel?
• Has the unit ever worked properly?
• If the unit used to work properly, try to determine
when the problem began.
• Does the problem occur randomly, frequently, or all the
time?
• What is the ambient temperature at the unit location?
Is it very hot or very cold?
• Did the problem begin after one of the following: a
severe lightning storm, fire, flood, or a plant accident?
• Has any water, refrigerant, or oil leaked into the panel
or conduit?
• Any recent changes in the system, for example soft-
ware or hardware?
• Any recent service to the controller, electrical system
or network?
• Check if the communications cable shields are tied to
machine ground at only one location. Ground the serial
comms, between the controller and the remote evapo-
rator I/O panels, at the Unity system controller only.
• If this is an older plant, has the plant wiring been
brought up to code?
• Is power wiring mixed with control wiring?
• Is power wiring mixed with sensor wiring?
• Is power wiring mixed with communications wiring?
• Ensure that pressure transducers are properly ground-
ed.
• Ensure that temperature transducers are properly
grounded.
• Check if one of the temperature probes has a signal
wire shorted to machine ground. To do this, first pull
the orange plug from the appropriate channel of the
Analog board and then use a DVM and check each
white wire to machine ground and each black wire to
machine ground.
• Check that all inductive loads, for example coils, sole-
noids, or relays, connected to the I/O output modules
have surge suppressers across them, preferably at the
devices and not at the panel end.
• Make sure there is a continuous ground back to the
power source. The ground connection must be alumi-
num or copper. A conduit ground will not work.
• Ensure there is no AC wiring lying next to any circuit
boards such as the controllers, analog or digital boards.
• Unexplainable unit failures are usually indicative of
noise due to wiring problems, for example incorrect
earth grounds, mixed power and control wiring, and
unsuppressed coils.
• If the unit is unexplainably shutting down, check if the
machine shares power with something else.
SECTION 7
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TROUBLESHOOTING
TROUBLESHOOTING