Carrier WeatherExpert 48N2 Controls, Start-Up, Operation, Service, And Troubleshooting page 106

PROBLEM
Unit Initiates a Humidi-MiZer
Dehumidification Mode, but
Supply Air Temperature is
Overheating/Overcooling the
Space
Low Sensible Capacity in Normal
Cooling Mode
Modulating Valves Not
Functioning Properly
Table 73 — Humidi-MiZer
CAUSE
Supply air set point for cooling is too
high/low
Evaporator discharge temperature
(CCT) or supply air temperature (SAT)
thermistor is reading incorrectly
Valve controlling gas bypass around
the condenser is not functioning
properly
Valve controlling refrigerant flow to the
condenser is not functioning properly
Modulating valves are not calibrated
properly
Unit control software indicates a
Humidi-MiZer Reheat Mode, but the 3-
way valve is not functioning properly.
Unit is not sized to meet the load at the
current entering air and outdoor
conditions.
Valve controlling gas bypass around
the condenser is stuck in an open
position or leaking.
Valve controlling refrigerant flow to the
condenser is stuck in a position less
than 100% open.
General cooling mode problem
Faulty wire connections
EXV board malfunction
Valve is stuck open/closed
Valve is not calibrated properly.
Service Analysis (cont)
®
Check the unit supply air set point for cooling operation. This is the
temperature that the valves will modulate to meet during a
dehumidification mode.
See "Thermistor Troubleshooting" on page 103.
Check if SAT thermistor is in a location that is measuring stratified air.
See "Modulating Valves Not Functioning Properly."
See "Modulating Valves Not Functioning Properly."
See "Modulating Valves Not Functioning Properly."
See "3-Way Valve Malfunction."
Check product data tables or ECAT for rated capacity at current
entering air and outdoor conditions.
See "Modulating Valves Not Functioning Properly."
See "Modulating Valves Not Functioning Properly."
See Table 72.
Check that the valve wiring is properly connected from the valve,
entering the control box and at the EXV board.
Check alarm history for A169 (Expansion Valve Control Board Comm
Failure.)
Use Service Test to manually manipulate the valve position and confirm
supply air temperature changes during operation.
Run valve calibration through Service Test.
Check valve motor for open or short circuited windings. Shut down
power to the unit and connect ohmmeter probes across the black and
white terminals. Resistance should measure 75 ohms ±10%. Next,
connect ohmmeter probes across the red and green terminals.
Resistance should measure 75 ohms ±10%. The meter should not
show an "open" or a "short" when a winding leg is measured. If either
occurs, replace the valve.
Run valve calibration through Service Test.
106
REMEDY