Digital Scroll Controller (Dsc) Troubleshooting - Carrier 50PD05 Operating And Service Instructions

Table 9 -- Cooling
Service Analysis
PROBLEM
Compressor and Fan Will Not Start
Compressor Cycles (other than
normally satisfying demand).
Compressor Operates
Continuously.
Excessive Condenser Pressures,
Condenser Fans Not Operating,
Excessive Suction Pressure,
Suction Pressure Too Low.
LEGEND
CB - Circuit Breaker
DSC - Digital Scroll Controller
TXV - Thermostatic Expansion 'Calve
VFD - X?ariable Frequency Drive
CAUSE
Power failure.
Fuse blown or circuit breaker tripped. Check CB1 and
CB2.
Disconnect off.
Compressor time guard to prevent short cycling.
Occupancy schedule set point or supply set point not
calling for Cooling.
Outdoor temperature too low.
Active alarm.
Insufficient line voltage.
Active alarm.
Unit undersized for load.
Occupancy schedule set point or supply set point too
low. Compressor running at lowest capacity
Compressor contactor stuck on
Dirty air filters.
Low refrigerant charge.
Condenser coil dirty or restricted.
Loose condenser thermistors.
Dirty condenser coil.
Refrigerant overcharge.
Faulty TXV.
Condenser air restricted or air short cycling.
Restriction in liquid tube.
No Power to contactors.
High heat load.
Faulty TXV.
Refrigerant overcharged.
Dirty air filters.
Low refrigerant charge.
Faulty TXV.
Insufficient evaporator airflow.
Indoor Fan Running to slow or off while compressor is
on
Temperature too low in conditioned area (low
return-air temperature).
REMEDY
Call power company.
Replace fuse or reset circuit breaker.
Power disconnect.
Check time guards using ComfortLink_' Scrolling
Marquee also the DSC has a 2 minute anti-short time
Check cooling demand using ComfortLink Scrolling
Marquee.
Check Compressor Lockout Temperature using
ComfortLink Scrolling Marquee.
Check active alarms using ComfortLink Scrolling
Marquee and DSC alert flash codes
Determine cause and correct.
Check active alarms using ComfortLink Scrolling
Marquee and DSC alert flash codes
Decrease load or increase size of unit.
Check and adjust set points if needed.
Check cooling demand using ComfortLink Scrolling
Marquee and DSC alert flash codes.
Replace filters.
Check pressure, locate leak, repair, evacuate, and
recharge.
Clean coil or remove restriction.
Tighten thermistors.
Clean coil.
Recover excess refrigerant.
1.Check TXV bulb mounting and secure tightly to suction
line and insulate.
2.Replace TXV (and filter drier) if stuck open or closed.
Determine cause and correct.
Remove restriction.
Fuse blown or plug at motor loose.
Check for sources and eliminate
1.Check TXV bulb mounting and secure tightly to suction
line and insulate.
2.Replace TXV (and filter drier) if stuck open or closed.
Recover excess refrigerant.
Replace air filters.
Check pressure, locate leak, repair, evacuate, and
recharge.
1.Check TXV bulb mounting and secure tightly to suction
line and insulate.
2.Replace TXV (and filter drier) if stuck open or closed.
Check belt tension. Check for other restrictions.
Check VFD display is illuminated and shows Auto
mode. Power supplied to VFD. Check O-lOvdc signal
present at AUXl board.
Reset thermostat or occupancy schedule.
Digital Scroll Controller (DSC) Troubleshooting
The 48/50PD units are equipped with a digital scroll compressor.
The compressor has a solenoid unloader that is controlled by the
digital scroll controller (DSC). This DSC turns the unloader on
and off within a 20 second window. The amount of time the
unloader is on verses off within that 20 seconds depends on the
desired capacity. This means that the ComfortLink control does
not have direct control of the compressor, but it does however
control the power to the DSC and the signal for commanded
capacity.
The DSC has three LED lights to help during troubleshooting;
green, yellow, and red The DSC will run the compressor
unloaded for a half a second on start up and one second on
shutdown to prevent reverse rotation. A two minute anti-short
time guard is applied by the DSC after shutting the compressor off.
The DSC has an alarm relay output that is connected to the MBB.
When this MBB input switch is closed, the MBB activates the
T051 alert. Check the LED status on the DSC for flash alarm
codes and correct any problems. Table 10 shows the DSC's Red
LED flash codes.
POWER LED (green) -- indicates voltage is present at the
24VAC power terminal. When the 2 minute anti-short cycle timer
is active, the green LED will flash.
UNLOADED LED (yellow) -- indicates the unloader solenoid
status. The LED is on when the unloader solenoid is energized.
ALERT LED (red) -- conmmnicates an abnormal system
condition through a unique flash code.
All LEDs Flashing at the Same Rate -- indicates 24VAC supply
is too low for operation.
All LEDs On Solid at the Same Time -- indicates Digital Scroll
Controller failure.
Flash Code 1 -- Reserved for future use
Flash Code 2 -- High Discharge Temperature
This occurs when the discharge temperature thermistor (DTT) has
31