FIGURE 57
UTEC INTEGRATED CIRCUIT BOARD
UNITEDTECHNOLOGIES
(UTEC)
(formerly Hamilton-Standard)
There have been several different
UTEC control boards used. All
performed the same function and had
the same components on the board.
Each had two green test lights. The
power light indicated the control had
24 volts to operate. The OK light
should be on constantly as the
control checks the circuitry. If the OK
light is off, the control detected an
internal problem or a system problem
and stopped the furnace. Both lights
should be on during normal
operation.
A WARNING: MAKE NO ATTEMPT
TO FIELD REPAIR/MODIFY ANY
SOLID STATE CONTROL UNLESS
SPECIFICALLY AUTHORIZED BY
THE FACTORY. DOING SO MAY
RESULT IN FURNACE MALFUNC-
TION CAUSING FIRE, EXPLOSION,
PERSONAL INJURY OR DEATH.
LOCK OUT STATUS
The control board reacts to
malfunctions within itself or in the
furnace system in two ways. One is a
"soft" lock out and the other is a
"hard" lock out.
In a
soft lock out both green lights
on the board are on. This could be
described as a wait state. Reset
the control either by cycling the
thermostat or the main power
disconnect. If the unit fails to sense a
microamp flame current in the normal
course of events, it goes into soft lock
out. This affects only the heating
mode. Cooling calls through the "Y"
and "G" terminals operate normally.
SOFT LOCK OUT CAUSES
1. Not detecting flame after four
ignition trials.
2. Failure of the pressure switch to
close after 60 seconds.
3. Four flame failures during one
heat call.
4. A software irregularity in the
microprocessor.
In a
hard lock out the control is
totally unresponsive and the "OK"
light is off. The power light remains
on. Resetting can only be accom-
plished by turning off main 120 volt
•
u
..
....
i
e..
~
;a
...
. ...
JI
.::,
%
power for 4 seconds and then
reapplying power.
HARD LOCK OUT CAUSES
1. Voltage to the gas valve out of
normal ignition sequence.
2. Low/no voltage to the gas valve
during normal operation.
3. Internal microprocessor or
external circuit failure
(hardware).
4. Abnormal power interruptions.
5. Transient voltage spikes on the
main power line.
►
NOTE: 1012-830/831/920/
920A/925/ 927/928 UTEC controls
normally do not go into hard lock out.
"SELF HEALING"
During development it was found that
the control could lock out with
downflow or horizontal units if the
heat assisted limit control (HALC)
trips during, or after, a furnace run
cycle. The HALC stops power to the
gas valve and the board retries for
ignition. With an open HALC, the gas
valve cannot open and the control
board would lock out.
62
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