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Universal Air Conditioning Unit
Faults and Error Messages
11 .4 Fault Codes and Indicator
Codes
Refer to the table if the Q3 control is displaying a fault
code or an indicator code.
Code
Description
Result
LO / AC
Operating voltage remained below the acceptable time limit for three minutes
or more (90 volts for a 100V system, 100 volts for a 115 V system).
Shutdown
HI / PS
The head pressure is above the maximum preset limit. This indicates a
condenser fan failure.
Shutdown
HP / - -
The high-pressure switch failed open circuit wires open.
Shutdown
LO / PS
The suction pressure is below the minimum preset limit. This indicates a loss of
gas, ambient temperature that is too low, evaporator fan failure, dirty filter, or
dirty coil.
Shutdown
LP / - -
The suction pressure is below the minimum preset limit, failed low-pressure
switch, or circuit wires are open.
Shutdown
IS / - - or - -
An inside temperature sensor failure flashes “IS/- -” for three seconds if the
Mode button is pressed. After three seconds, the Q3 control shows a constant
“- -”. Cool or Heat Mode may be selected for emergency operation and the
display will show a constant “- -”.
Emergency Operation
Ar / FL
The Q3 control flashes “Ar / FL” for 15 seconds every 30 minutes indicating
the Return-Air Filter needs to be cleaned or replaced. Reset and stop the
flashing by pressing the Fan, Up, and Down buttons simultaneously.
Continue Operation
LC
“LC” flashes momentarily if a button is pressed indicating the Q3 control is
locked in the current mode of operation. Enter or exit lock mode by pressing
the Mode, Up, and Fan buttons simultaneously. “UL” flashes for three seconds
when exiting lock mode.
Continue Operation
OU / 1st digit / 2nd
2 digits or OU
The Q3 control displays the optional outside temperature as “OU” then the
first digit followed by second two digits. The Q3 control displays “OU” if the
optional outside temperature sensor is not installed or failed open or shorted.
See “Understanding Button Functions” on page 15.
Continue Operation
LO / SE
“LO/SE” will display if the optional thermal couple was plugged into the blue
port. Plug the optional thermal couple into the red port.
Shutdown or Switch to
Optional Electric Heat
