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Humidi-MiZer® System Troubleshooting
Use the SystemVu™ control display or a CCN device to view
the cooling status display and the cooling diagnostic display. See
“Optional Humidi-MiZer Dehumidification System” on page 21
for information on the cooling operation and the related Humidi-
MiZer system operation. Check the current alarms and alarm
history for any cooling alarm codes and correct any causes (see
Table 16 on page 38). Verify any unique control configurations
per installed site requirements or accessories.
If alarm conditions are corrected and cleared, operation of the
compressors, fans, and Humidi-MiZer system valves may be
verified by using the Service Test mode (see Table 4 on
page 13). In addition to general cooling service analysis
(Table 18), see Table 19 on page 42 for general Humidi-MiZer
system service analysis.
NOTE: Wiring, operation, and charge are different on a Humidi-
MiZer system unit compared to a standard unit.
Table 17 — Communication Resistances
DEVICE
(LEN) RESISTANCE BETWEEN
PINS / CONNECTOR
(BAS) RESISTANCE BETWEEN
PINS / CONNECTOR
(RNET) RESISTANCE BETWEEN
PINS / CONNECTOR
Pins
1 to 3
Pins
1 to 2
Pins
2 to 3
Pins
1 to 3
Pins
1 to 2
Pins
2 to 3
Pins
GND to +
Pins
GND to -
Pins
+ to -
MBB 19.92 KΩ 10.63 KΩ 9.51 KΩ 19.92 KΩ 10.63 KΩ 9.51 KΩ 2.25 KΩ 1 KΩ 3.3 KΩ
Table 18 — Cooling Service Analysis
PROBLEM CAUSE REMEDY
Compressor and Fan
Will Not Start
Power failure. Call power company.
Fuse blown or circuit breaker tripped. Replace fuse or reset circuit breaker.
Disconnect off. Power disconnect.
Compressor time guard to prevent short cycling. Check using SystemVu Display.
Thermostat or occupancy schedule set point not
calling for cooling.
Check using SystemVu Display.
Outdoor temperature too low.
Check Compressor Lockout Temperature using SystemVu
Display.
Active alarm. Check active alarms using SystemVu Scrolling Marquee.
Compressor Cycles (other than
normally satisfying thermostat)
Insufficient line voltage. Determine cause and correct.
Active alarm. Check active alarms using SystemVu Scrolling Marquee.
Compressor Operates
Continuously
Unit undersized for load. Decrease load or increase size of unit.
Thermostat or occupancy schedule set point too
low.
Reset thermostat or schedule set point.
Dirty air filters. Replace filters.
Low refrigerant charge.
Check pressure, locate leak, repair, evacuate, and
recharge.
Condenser coil dirty or restricted. Clean coil or remove restriction.
Excessive Condenser
Pressures
Dirty condenser coil. Clean coil.
Refrigerant overcharge. Recover excess refrigerant.
Faulty TXV.
1. Check TXV bulb mounting and secure tightly to suction
line and insulate.
2. Replace TXV (and filter drier) if stuck open or closed.
Condenser air restricted or air short cycling. Determine cause and correct.
Restriction in liquid tube. Remove restriction.
Condenser Fans Not Operating No power to contactors. Fuse blown or plug at motor loose.
Excessive Suction Pressure
High heat load. Check for sources and eliminate.
Faulty TXV.
1. Check TXV bulb mounting and secure tightly to suction
line and insulate.
2. Replace TXV (and filter drier) if stuck open or closed.
Refrigerant overcharged. Recover excess refrigerant.
Suction Pressure Too Low
Dirty air filters. Replace air filters.
Low refrigerant charge.
Check pressure, locate leak, repair, evacuate, and
recharge.
Faulty TXV.
1. Check TXV bulb mounting and secure tightly to suction
line and insulate.
2. Replace TXV (and filter drier) if stuck open or closed.
Insufficient evaporator airflow. Check belt tension. Check for other restrictions.
Temperature too low in conditioned area (low
return-air temperature).
Reset thermostat or occupancy schedule.
LEGEND
TXV — Thermostatic Expansion Valve
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