11. Service
CAUTION
CAUTION: Servicing the UA-90H with its high pressure
refrigerant system and high voltage circuitry presents a health
hazard which could result in death, serious bodily injury, and/
or property damage. Call your HVAC contractor.
11.1 Technical Description
The UA-90H uses a refrigeration system similar to an air
conditioner’s to remove heat and moisture from incoming air, and
add heat to the air that is discharged. Hot, high-pressure refrigerant
gas is routed from the compressor to the condenser coil (See Figure
1). The refrigerant is cooled and condensed by giving up its heat to
the air that is about to be discharged from the unit. The refrigerant
liquid then passes through a strainer and capillary tubing which
causes the refrigerant pressure and temperature to drop. It next
enters the evaporator coil where it absorbs heat from the incoming
air and evaporates. The evaporator operates in a flooded condition,
which means that all the evaporator tubes contain liquid refrigerant
during normal operation. A flooded evaporator should maintain
nearly constant pressure and temperature across the entire coil,
from inlet to outlet.
The mixture of gas and liquid refrigerant enter the accumulator
after leaving the evaporator coil. The accumulator prevents any
liquid refrigerant from reaching the compressor. The compressor
evacuates the cool refrigerant gas from the accumulator and
compresses it to a high pressure and temperature
11.2 Troubleshooting
No dehumidification, neither fan nor compressor run with fan
switch and ventilation timer OFF.
1. Unit unplugged or no power to outlet.
2. Humidity control set too high or defective.
3. Loose connection in internal or control wiring.
4. Defective Compressor relay.
5. Defective control transformer.
6. Optional Condensate Pump Safety Switch open.
No dehumidification, compressor does not run but fan runs
with fan switch and ventilation timer OFF and humidity control
turned to ON.
1. Defective compressor run capacitor.
2. Bad connection in compressor circuit.
3. Defective compressor overload.
4. Defective compressor.
5. Defrost thermostat open.
6. Optional Condensate Pump Safety Switch open.
Fan runs with fan switch and ventilation timer OFF, but
compressor cycles on and off.
1. Low ambient temperature and/or humidity causing unit to
cycle through defrost mode.
2. Defective compressor overload.
3. Defective compressor.
4. Defrost thermostat defective.
5. Dirty air filter(s) or airflow restricted.
6. Low refrigerant charge, causing defrost control to cycle.
7. Bad connection in compressor circuit. Fan does not run with
fan switch in either position.
Fan does not run with ventilation timer activated. Compressor
runs briefly but cycles on & off with humidity control turned to
ON.
1. Loose connection in fan circuit.
2. Obstruction prevents fan rotation.
3. Defective fan.
4. Defective fan relay.
5. Defective fan capacitor.
Fan runs with fan switch ON. Fan does not run with ventilation
timer activated.
1. Defective ventilation timer.
2. Time not correct on ventilation timer.
3. Ventilation timer set to manual and switched OFF.
4. Defective fan switch.
Evaporator coil frosted continuously, low dehumidifying
capacity.
1. Defrost thermostat loose or defective.
2. Low refrigerant charge.
3. Dirty air filter(s) or airflow restricted.
4. Excessively restrictive ducting connected to unit.
FOR HVAC INSTALLER ONLY
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Ultra-Aire 90H Installer’s & Owner’s Manual
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Ultra-Aire 90H Installer’s & Owner’s Manual
Refrigeration System of UA-90H
