Reznor MAPS II Unit Installation Manual - Manual (Page 54)

Form I-MAPS II, Page 54
Sequence of Cooling Operation when ambient temperature is BELOW
68°F/20°C (all Models):
NOTE: Outdoor ambient lockouts may prevent mechanical cooling or reheat.
Temporarily override lockouts by lowering the oC1 programmable control set-
ting to 58°F. To enable unit reheat functions, temporarily lower the DP1 set-
ting to 50°F. If ambient conditions (below 58°F) still prevent mechanical cool-
ing operation, the outside air sensor can be warmed by hand or replaced with
a 14 watt, 1000 to 1200 Ohm resistor. When testing is complete, reset oC1 or
DP1 as required by the application. (For instructions on changing settings on
the programmable control, refer to the instruction sheet for the control system
shipped either in the Literature Bag or with the Wiring Diagram.)
1. Set control switch at Auto position (closed).
A) Energizing the blower motor, and if equipped, the damper motor.
B) Air proving switch closes, allowing for heating, cooling, or reheat
mode.
1) On temperature rise above outside air changeover setting,
a) Energizing the re-heat heat pump circuit after minimum time
delay (RDA, RDDA, REDA).
b) Cooling rate controlled by discharge air sensor.
c) On call for cooling, the corresponding compressors and con
denser motors are energized.
d) On low humidity or abnormal temperature, the re-heat heat
pump is de-energized (RDA, RDDA, REDA only).
e) On abnormal temperature, the corresponding cooling circuit is
de-energized.
2) On temperature drop below changeover setting, the cooling circuit
is de-energized.
2. For shutdown, set control switch at OFF position (open).
SPECIAL Startup Cooling Sequence when ambient temperature is
BELOW 68°F/20°C
 Verify that the blower and all condenser fans are rotating in the proper
direction. If blower rotation is incorrect, change phase at the field line volt-
age connection. Compressor rotation is phase sensitive.
 Check the superheat and subcooling.
Superheat is the verification that the evaporator coil is properly using the
refrigerant supplied. Too much superheat indicates that the coil is under-
charged. Too little superheat indicates that the coil is overcharged and
potentially flooding liquid refrigerant to the compressor.
Subcooling is the measurement of liquid refrigerant stored in the con-
denser coil. Too much subcooling indicates a system overcharge. Too little
indicates a system undercharge and may not provide the thermal expan-
sion valve with a full column of liquid refrigerant for proper operation.
Two important requirements before checking superheat and subcool-
ing:
1) This unit has fully intertwined refrigerant circuits and each circuit MUST
be isolated before measuring its temperature. Another active circuit will
influence the reading and make it impossible to determine accurate super-
heat and subcooling.
2) If the circuit is equipped with an optional hot gas bypass valve, the valve
must be disabled before measuring superheat and subcooling. Disable
the hot gas bypass valve by removing the cover and adjusting the spring
IMPORTANT:
All refrigeration
checks must be
made by a qualified
refrigeration
technician.
10. Commissioning
and Startup
(cont'd)
10.3 Checklist
Startup (cont'd)
10.3.1 Startup Checklist for ALL Systems (cont'd)