86
determining the resistance with unit shut down and thermistor
disconnected from J8. Compare the values determined with the
value read by the control in the Temperatures mode using the
scrolling marquee display.
Transducer Troubleshooting — The electronic con-
trol uses 2 suction pressure transducers to measure the suction
pressure of circuits A and B. The pressure/voltage characteris-
tics of these transducers are in shown in Tables 76 and 77. The
accuracy of these transducers can be verified by connecting an
accurate pressure gage to the second refrigerant port in the
suction line.
Table 71 — Cooling Service Analysis
LEGEND
PROBLEM CAUSE REMEDY
Compressor and Fan Will Not
Start.
Power failure. Call power company.
Fuse blown or circuit breaker tripped. Check CB1,
CB2, and CB3.
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 call-
ing for Cooling.
Check using ComfortLink scrolling marquee.
Outdoor temperature too low. Check Compressor Lockout Temperature (MC.LO)
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.
Compressors Operates
Continuously.
Unit undersized for load. Decrease load or increase of 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 Head 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 for leaks, repair, 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.
CB — Circuit Breaker
TXV — Thermostatic Expansion Valve