Carrier 48/50PD05 manual Digital Scroll Controller DSC Troubleshooting, Cooling Service Analysis

Table 9 — Cooling Service Analysis

PROBLEM	CAUSE	REMEDY
Compressor and Fan Will Not Start	Power failure.	Call power company.
	Fuse blown or circuit breaker tripped. Check CB1 and	Replace fuse or reset circuit breaker.
	CB2.
	Disconnect off.	Power disconnect.
	Compressor time guard to prevent short cycling.	Check time guards using ComfortLinkt Scrolling
		Marquee also the DSC has a 2 minute anti---short time
	Occupancy schedule set point or supply set point not	Check cooling demand using ComfortLink Scrolling
	calling for Cooling.	Marquee.
	Outdoor temperature too low.	Check Compressor Lockout Temperature using
		ComfortLink Scrolling Marquee.
	Active alarm.	Check active alarms using ComfortLink Scrolling
		Marquee and DSC alert flash codes
Compressor Cycles (other than	Insufficient line voltage.	Determine cause and correct.
normally satisfying demand).
	Active alarm.	Check active alarms using ComfortLink Scrolling
		Marquee and DSC alert flash codes
Compressor Operates	Unit undersized for load.	Decrease load or increase size of unit.
Continuously.
	Occupancy schedule set point or supply set point too	Check and adjust set points if needed.
	low. Compressor running at lowest capacity
	Compressor contactor stuck on	Check cooling demand using ComfortLink Scrolling
		Marquee and DSC alert flash codes.
	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.	Loose condenser thermistors.	Tighten thermistors.
	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.
	Indoor Fan Running to slow or off while compressor is	Check VFD display is illuminated and shows Auto
	on	mode. Power supplied to VFD. Check 0---10vdc signal
		present at AUX1 board.
	Temperature too low in conditioned area (low	Reset thermostat or occupancy schedule.
	return---air temperature).
LEGEND
CB - Circuit Breaker
DSC - Digital Scroll Controller
TXV - Thermostatic Expansion Valve
VFD - Variable Frequency Drive

48/50PD

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) ⎯ communicates 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

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