75
Alarm Code 60 (Return-Air Thermistor Failure)
— If the
temperature measured by this thermistor is outside the range of
–40 to 245 F (–40 to 118 C), the cooling capacity algorithm
will use a default of 8º F per stage drop. Heating and economiz-
er will be disabled. Reset of this alarm is automatic once the
problem is corrected. Start-up follows the normal sequence.
The cause of the alarm is usually a bad thermistor, a shorted or
open thermistor caused by a wiring error, or a loose connection.
Alarm Code 61 (Outdoor-Air Thermistor Failure)
— If the
temperature measured by this thermistor is outside the range of
–40 to 245 F (–40 to 118 C), the economizer routine will use
enthalpy input only. If the unit is equipped with humidity sen-
sors, then the enthalpy will also be considered bad and the
economizer will close the dampers. Nighttime free cooling will
also be disabled. Reset of this alarm is automatic once the prob-
lem is corrected. Start-up follows the normal sequence. The
cause of the alarm is usually a bad thermistor, a wiring error, or
a loose connection.
Alarm Codes 62 and 63 (Saturated Condensing Thermistor
Failure) — If the SCT fails (temperature is out of the range of
–40 F to 245 F), the alarm will trip and the appropriate circuit
will shut off. Reset of this alarm is automatic once the problem
is corrected. The unit performs a complete restart when the
SCT sensor resets. The cause of the alarm is usually a bad ther-
mistor, a wiring error, or a loose connection.
NOTE: This alarm is only valid when the unit has saturated
condensing thermistors.
Alarm Codes 64 and 65 (Suction Thermistor Failure)
— If
the temperature measured by this thermistor is outside the
range of –40 to 245 F (–40 to 118 C), the high and low super-
heat alarms will be disabled and the head pressure algorithm
will operate as if the unit did not have suction sensors. Reset of
this alarm is automatic once the problem is corrected. Start-up
follows the normal sequence. The cause of the alarm is usually
a bad thermistor, a wiring error, or a loose connection.
Alarm Code 66 (Space Thermistor Failure)
— This alarm
applies to all units. If the temperature measured by this ther-
mistor is outside the range of –10 to 245 F (–23 to 118 C), the
temperature reset, nighttime free cooling, and cooling and
heating (CV applications only) functions are disabled. Reset of
this alarm is automatic once the problem is corrected, and the
reset function will be enabled. The cause of the alarm is usu-
ally a bad thermistor, a wiring error, or a loose connection.
Alarm Codes 67 through 70 (Transducer Failure)
— If the
voltage ratio of a transducer is less than 2% or greater than
98% for 3 seconds, the transducer has failed and the affected
circuit shuts down.
Code 67 — Compressor A1 Discharge Pressure
Transducer Failure
Code 68 — Compressor B1 Discharge Pressure
Transducer Failure
Code 69 — Compressor A1 Suction Pressure
Transducer Failure
Code 70 — Compressor B1 Suction Pressure
Transducer Failure
The reset of this alarm is automatic if the voltage ratio re-
turns within range. Start-up of this circuit follows a normal se-
quence. The cause of this error is usually a bad transducer, a
bad 5-v power supply, or a wiring error. The failed transducer
should be recalibrated by the control using the service function
before the transducer is considered bad.
Alarm Code 71 (Loss of Communications With DSIO1)
—
If communication is lost with the DSIO1 module, all outputs
controlled by this module will be turned off. This alarm will re-
set automatically when the communication is restored. The
outputs will turn on normally after the alarm condition has
been reset. The probable cause for this condition is a faulty or
improperly connected plug, a wiring error, or a faulty module.
Alarm Code 72 (Loss of Communications With DSIO2)
—
If communication is lost with the DSIO2 module, all outputs
controlled by this module will be turned off. This alarm will re-
set automatically once the communication is restored. The out-
puts will turn on normally after the alarm condition has been
reset. The probable cause for this condition is a faulty or im-
properly connected plug, a wiring error, or a faulty module.
Alarm Code 73 (Loss of Communications With Control
Options Board [PSIO2]) — If communication is lost with the
PSIO2 module, all outputs controlled by this module will be
turned off. Reset of this alarm is automatic when the communi-
cation is restored.
Start-up after this alarm has been remedied follows a
normal sequence. The probable cause for this condition is a
faulty or improperly connected plug, a wiring error, or a faulty
module.
Alarm Codes 74 and 75 (Low Pressure Circuit A or B)
With low-pressure switches installed — If a circuit is on and
the low-pressure switch is open (opens at 27 psig ± 4 psig) for
15 seconds, the compressor in that circuit will stop and the
alarm will trip.
NOTE: During initial start-up of a circuit, the low pressure
input will be ignored for 2 minutes.
With a suction transducer installed — If a circuit is on and the
suction pressure drops below 28 psig for 15 seconds, the com-
pressor in that circuit will stop and the alarm will trip.
Alarm code 74 signals a circuit A failure, and code 75 sig-
nals a circuit B failure. The reset for this alarm can be automat-
ic if the pressure reaches 67 ± 7 psig (switch) or 65 psig (trans-
ducer) within 5 minutes after the alarm has tripped. The circuit
will not be reset if it trips again after 3 consecutive failures. The
possible causes for the alarm are low refrigerant charge, dirty
filters, evaporator fan turning backwards, inlet guide vanes not
opening properly, plugged filter drier, or faulty transducer.
Alarm Codes 76 and 77 (High Pressure Circuit A or B)
—
If a compressor trips on compressor fault alarm 51 or 55 and
the discharge pressure for that circuit is greater than 410 psig,
then the high pressure alarm will trip. If the discharge pressure
ever exceeds 440 psig, then the alarm will trip and the appro-
priate circuit will be shut off.
Alarm code 76 signals a circuit A failure, and alarm code 77
signals a circuit B failure.
Reset of this alarm is manual. The circuit will start normally
after the alarm condition has been corrected. Possible causes
for this alarm are an overcharged system, high outdoor ambient
temperature coupled with a dirty outdoor coil, plugged filter
drier, partially closed liquid line service valve, or a faulty
transducer.
NOTE: This alarm is only valid when the unit has refrigerant
pressure transducers.
Alarm Code 78 (Supply-Air Fan)
— If the commanded state
and status of the supply-air fan do not match for 60 seconds,
the alarm trips. (The control circuit does not detect circuit
breaker failures due to motor overcurrent, shorts or grounds be-
tween the evaporator-fan circuit breaker and motor, circuit
breaker trips, or broken belts.) Other possible causes are fan
status switch failure, tubing not properly connected, or switch
set improperly. All other unit outputs except the supply-air fan
are turned off when this alarm is generated. The supply-air fan
output remains energized.
Reset of this alarm is automatic once the problem is
corrected.
Alarm Codes 80 and 81 (Low Saturated Suction Tempera-
ture) — If the saturated suction temperature is less than 20 F
(–6.7 C) for 5 minutes, the alarm trips and the circuit shuts off.
If the unit is configured for 2-speed fan operation, the fan
must be on high speed for this alarm to be generated. If the fan
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