290699-YIM-B-0607
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Unitary Products Group
NOTE:
While the above step will reset any lockouts,
the compressor may be held off for the ASCD.
See the next step.
10. If 24 volts is present at the UCB Y1 terminal and
none of the switches are open and the compressor
is not locked out, the UCB may have the compres-
sor in an ASCD. Check the LED for an indication of
an ASCD cycle. The ASCD should time out within
5 minutes. Press and release the TEST button to
reset all ASCDs.
11. If 24 volts is present at the UCB Y1 terminal and the
compressor is not out due to a protective switch trip,
repeat trip lock out, or ASCD, the economizer termi-
nals of the UCB may be improperly wired. Check for
24 volts at the Y1 “OUT” terminal of the UCB. If 24
volts is present, trace the wiring from Y1 “OUT” for
incorrect wiring. If 24 volts is not present at the Y1
“OUT” terminal, the UCB must be replaced.
12.
For units without economizers
: If 24 volts is
present at the Y1 OUT terminal, check for 24 volts
at the Y1 “ECON” terminal. If 24 volts is not
present, check for loose wiring from the Y1 “OUT”
terminal to the Mate-N-Lock plug, the jumper in the
Mate-N-Lock plug, and in the wiring from the Mate-
N-Lock plug to the Y1 “ECON” terminal.
13.
For units with economizers
: If 24 volts is present at
the Y1 “OUT” terminal, check for 24 volts at the Y1
“ECON” terminal. If 24 volts is not present, check
for loose wiring from the Y1 “OUT” terminal to the
Mate-N-Lock plug, a poor connection between the
UCB and economizer Mate-N-Lock plugs, loose
wiring from the Mate-N-Lock plug to the econo-
mizer, back to the Mate-N-Lock plug, and from the
Mate-N-Lock plug to the Y1 “ECON” terminal. If
nothing is found, the economizer actuator may
have faulted and is failing to return the 24-volt “call”
to the Y1 “ECON” terminal even though the econo-
mizer is not providing free cooling. To test, discon-
nect the Mate-N-Locks and jumper between the
WHITE and YELLOW wires of the UCB’s Mate-N-
Lock plug. If the compressor energizes, there is a
fault in the economizer wiring or actuator.
14. The UCB can be programmed to lock out compres-
sor operation during free cooling and in low ambi-
ent conditions. These options are not enabled by
default. Local
distributors can test the UCB for this
programming.
For units with factory installed economizers, the
UCB is programmed to lock out compressor opera-
tion when the LAS set point is reached.
For units without factory installed or with field
installed economizers, the UCB allows compressor
operation all the time. This programming can be
checked or changed by the local distributor.
15. If none of the above correct the error, replace the
UCB.
GAS HEAT TROUBLESHOOTING GUIDE
Before beginning symptomatic troubleshooting activi-
ties read the flash code LEDs on the unit control board
(UCB) and the ignition control board (ICB). Fault codes
have a quick sequence of flashes indicating the flash
code number followed by a pause with the LED off. The
ICB flash codes are repeated until the fault is cleared.
The ICB monitors itself, the centrifugal switch, lockout
Troubleshooting of components may require
opening the electrical control box with the power
connected to the unit.
Use extreme care when
working with live circuits!
Check the unit
nameplate for the correct line voltage and set the
voltmeter to the correct range before making any
connections with line terminals.
When not necessary, shut off all electric power to
the unit prior to any of the following maintenance
procedures so as to prevent personal injury.
Label all wires prior to disconnection when ser-
vicing controls. Wiring errors can cause improper
and dangerous operation, which could cause
injury to person and/or damage unit components.
Verify proper operation after servicing.
The furnace may shut down on a high tempera-
ture condition during the procedure. If this
occurs, the UCB energize the supply air blower
motor until the high temperature limit has reset.
Caution should be used at all times as the supply
air blower may energize regardless of the room
thermostat fan switch position.
