Carrier 48HC 04-28 - Cooling Troubleshooting; Cooling Service Analysis and Problem Resolution

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Cooling Troubleshooting
Use the scrolling marquee display or a CCN device to view the
cooling status display and the cooling diagnostic display (see
Appendix A) for information on the cooling operation. Check
the current alarms and alarm history for any cooling alarm
codes and correct any causes. (See Table 14.) Verify any
unique control configurations per installed site requirements or
accessories.
If alarms conditions are corrected and cleared, operation of the
compressors and fans may be verified by using the Service Test
mode. (See Table 6.) See Table 16 for general cooling service
analysis.
Table 16 — 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 ComfortLink scrolling marquee.
Thermostat or occupancy schedule set point not
calling for Cooling.
Check using ComfortLink scrolling marquee.
Outdoor temperature too low. Check Compressor Lockout Temperature using
ComfortLink scrolling marquee.
Active alarm. Check active alarms using ComfortLink scrolling
marquee.
Compressor Cycles (other than normally
satisfying thermostat).
Insufficient line voltage. Determine cause and correct.
Active alarm. Check active alarms using ComfortLink 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. 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.
Temperature too low in conditioned area (low
return-air temperature).
Reset thermostat or occupancy schedule.
Compressor not running but ComfortLink
Status show it is on.
Condensate overflow switch, High pressure, or
Freeze protection thermostat has tripped.
Check Alarms. (T051 or T055), check switches
and conditions that can cause their trips.
LEGEND
TXV — Thermostatic Expansion Valve