Carrier 40UV Installation, Start-Up And Service Instructions Manual page 71

PROBLEM
Indoor Air Quality (IAQ)
Features Malfunctioning
LLT Trips Frequently
IAQ Level Exceeds
Set Point Frequently
(Generated Alarms)
LEGEND
DX — Direct Expansion
IAQ — Indoor Air Quality
LED — Light Emitting Diode
LLT — Low-Limit Thermostat
MAT — Mixed-Air Temperature Sensor
MIX1 — Mixed Air 1Terminal
MIX2 — Mixed Air 2 Terminal
OA — Outdoor Air
OAT — Outdoor-Air Temperature Sensor
RH — Relative Humidity
RAT — Return-Air Temperature
SPT — Space Temperature Sensor
TB — Terminal Box
Table 30 — Unit Diagnostics and Troubleshooting (cont)
POSSIBLE CAUSE
IAQ not enabled
Set point too high/too low
Space or return air temperature too high/low
Space Relative Humidity too high
MAT sensor is shorted, open, or forced
LLT switch malfunctioning
MAT sensor failed or out of calibration
Maximum output value set too low
OAT sensor failed or open
CORRECTIVE ACTION
Enable IAQ control operation.
Adjust the set point to the correct value.
Control will resume when space/returns temperatures
recover.
Control will resume when relative humidity recovers.
Verify high humidity limit is configured properly. Reset to
100% if RH control is not used.
Normal operation will resume when MAT sensor is
operating properly. Remove Force; repair or replace MAT
sensor.
Replace LLT switch.
Verify MAT sensor is reading correctly. Trim or replace if
necessary.
Verify maximum output value has been correctly set.
Increase value in 10% increments.
Normal operation will resume when OAT sensor is
repaired.
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