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Table 19 — Humidi-MiZer System Service Analysis
PROBLEM CAUSE REMEDY
Subcooling Reheat Mode
Will Not Activate
General cooling mode problem. See Cooling Service Analysis (Table 18).
No dehumidification demand. See No Dehumidification Demand, below.
IOB operation. See IOB Operation, below.
Circuit LDV valve problem. See LDV Valve Operation, below.
Hot Gas Reheat Mode
Will Not Activate
General cooling mode problem. See Cooling Service Analysis (Table 18).
No dehumidification demand. See No Dehumidification Demand, below.
IOB operation. See IOB Operation, below.
Circuit LDV valve problem. See LDV (3-Way) Valve Operation, below.
Circuit RDV valve is not open. See RDV Valve Operation, below.
Outdoor temperature too low.
Check Reheat Circuit Limit Temperatures Unit
Configurations Cooling Humz Lockout OAT
No Dehumidification Demand
Relative humidity setpoint is too low —
Humidistat
Check/reduce setting on accessory humidistat.
Relative humidity setpoint is too low — RH
sensor.
Check Space RH Setpoints (Setpoints SPRH)
Software configuration error for accessory
humidistat.
Check Space Humidity Switch (SETTINGS UNIT
CONFIGURATIONS SWITCH INPUTS CONFIGS
HUMSTAT CHANNEL)
Software configuration error for accessory
humidity sensor.
Check RH Sensor (SETTINGS UNIT
CONFIGURATIONS ANALOG INPUTS CONFIGS
SPRH SENSOR CHANNEL)
No humidity signal. Check wiring. Check humidistat or humidity sensor.
IOB Operation
Communication loss to Input-Output Board.
Check wiring connections. Alert A099 - COMM LOSS
WITH SIOB.
No power to output terminals. Check wiring.
Relay outputs do not change state. Replace faulty IOB.
LDV (3-Way) Valve Operation
No 24v signal to input terminals.
Check using Service LIQ DIVERT A TEST
Check IOB relay output.
Check wiring.
Check transformer and circuit beaker or fuses.
Solenoid coil burnout.
Check continuous over-voltage is less than 10%.
Check under-voltage is less than 15%.
Check for missing coil assembly parts.
Check for damaged valve enclosing tube.
Stuck valve. Replace valve. Replace filter drier.
RDV Valve Operation.
(NOTE: Normally Closed
When De-energized)
No 24v signal to input terminals.
Check using Service RDV A TEST
Check IOB relay output.
Check wiring.
Check transformer and circuit breaker or fuses.
Solenoid coil burnout.
Check continuous over-voltage is less than 10%.
Check under-voltage is less than 15%.
Check for missing coil assembly parts.
Check for damaged valve enclosing tube.
Stuck valve. Replace valve. Replace filter drier.
Low Sensible Capacity in Normal Cool
or Subcooling Reheat Modes
RDV valve open or leaking. See RDV Valve Operation, above.
Low Suction Pressure and High
Superheat During Normal Cool Mode
General cooling mode problem. See Cooling Service Analysis (Table 18).
RDV valve open or leaking. See RDV Valve Operation, above.
RDV Valve Cycling On/Off Hot Gas Reheat mode low suction pressure limit.
Normal Operation During Mixed Circuit Subcooling
and Hot Gas Reheat Modes at Lower Outdoor
Temperatures.
LEGEND
IOB — Input-Output Board
LDV — Liquid Diverter Valve
RDV — Reheat Discharge Valve
RH — Relative Humidity
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