3
ST 5110
QM 1329.rev.00
CAUSE
SOLUTION
PROBLEM
The stage 1
variable speed
cooling fans are
not running.
(continued)
The minimum
speed is too low.
Adjust the minimum speed to
a higher value.
The fan motor is
defective.
Check if the motor is defective
by connecting it to an alternate
power supply. If it still is not
operating, replace the motor.
The stage 1
variable speed
cooling fans run
erratically.
The selected motor
curve is inappropri-
ate.
Select an appropriate motor
curve. Refer to "motor curves"
The stage 1 differ-
ential is too small.
Adjust the stage 1 differential
to a higher value.
The stage 1 time on
or time off is too
short.
Adjust the stage 1 time on or
time off to a higher value.
A variation in
resistance induced
on a room probe
causes this probe
to measure sudden
variations in the
room temperature.
Be sure the room probes are
dry. Locate them away from
drafts and sources of radiant
heating.
Electrical noise
near a room probe
cable causes this
probe to measure
sudden variations in
the room tempera-
ture.
Isolate the room probe cables
from all high voltage sources.
Do not route probe cables and
other power cables through
the same electrical knockout.
Do not run probe cables next
to other power cables. When
crossing other power cables,
cross at 90°.
