Munters HCUw, Operating & Maintenance

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incorrectly wired.
3.7 CONNECTING THE CONTROL SYSTEM
The unit is controlled by a
Novar IOM or Danfoss controller
with relay outputs. Digital inputs monitor
faults. With this method of control, the fan relay on the IOM turns the unit on. The relays on the BMS IO
card call for stages of cooling, dehumidification and heating as conditions require.
The HCU has eight (8) control inputs for the functions of fan, cooling stage 1, cooling stage 2, and
dehumidification. Heating stages 1 through 4 are controlled directly by the IOM. See Section 4 for details.
The HCU microprocessor is connected to the Novar IOM according to wiring diagram 5900-03 for a single
heater unit or 5900-00 for a two heater unit (Appendix B).
3.8 START-UP CHECKS
There are a couple of points that should be checked before the unit can be released for normal service:
1. A unit using three-phase AC may be wired so the compressor is operating backwards. A unit that is
wired this way may make an unusual sound, and will not produce any cooling. The microprocessor
will indicate “Compressor Low Diff Press” alarm after a 5 minute delay. To correct this problem, see
Section 3.5. If the compressors will not energize, check adjustment on the Airflow switch. The supply
fan must close the airflow switch for the compressors to operate.
2. Turn on power to the unit and allow it to operate normally for about 30 minutes. (This will allow time
for the temperatures inside the unit to stabilize.) You should run this test at a time of day when the
HCU needs to run dehumidification. Using a simple probe thermometer, check the temperatures
leaving (LAT) the cooling coil, desiccant wheel, and condenser coil. The cooling coil LAT should be
15 to 30 degrees F cooler than ambient. The wheel LAT should be 10 to 15 degrees F warmer than
the coil LAT. The condenser coil LAT should be at least 112 degrees F.