Reznor MAPS III, Cabinet D RECB Users Manual - Manual (Page 17)

Form O-MAPSIII Cabinet D, P/N 222918R9, Page 17
CAUTION: Be sure to connect pressure gauges to the suction
and discharge lines before system start-up so that compressor
rotation can be checked immediately. Scroll compressors will be
destroyed if allowed to operate in the wrong direction. See Hazard
Levels, page 2.
Record the ambient temperature. Adjust the system controller so that a call for
cooling exists.
NOTE: Outdoor ambient lockouts may prevent mechanical cooling. Temporarily
override lockouts by lowering the cooling setpoint. When testing is complete, reset
the controller.
Because it is possible to unknowingly connect 3-phase power in such a way
as to cause the scroll compressor or blower to rotate in reverse, it is very
important to check this on startup.
Check Compressors - Immediately at startup, observe the gauges. If the
suction pressure rises and discharge pressure drops, the compressor is
operating in reverse and must be shut down. Turn off the power and switch
the 3-phase line voltage wiring connections before restarting the unit.
(Important NOTE: If allowed to operate for several minutes in reverse, the
compressor’s internal protector will trip. If a compressor is repeatedly
allowed to restart and run in reverse, the compressor will be permanently
damaged.)
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Step 11. Check Subcooling and Superheat
Superheat is the verification that the evaporator coil is properly using the
refrigerant supplied. Too much superheat indicates that the coil is undercharged.
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 condenser
coil. Too much subcooling indicates a system overcharge. Too little subcooling
indicates a system undercharge and may not provide the thermal expansion valve
with a full column of liquid refrigerant for proper operation.
Two important requirements before checking superheat and subcooling:
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 superheat and subcooling.
2) If equipped with an optional hot gas bypass, disable the hot gas bypass valve
before charging. The method of disabling the bypass valve depends on whether or
not there is a shutoff valve in the line between the compressor discharge and the
hot gas bypass valve.
If there is a shutoff valve in the line between the compressor discharge and the
hot gas bypass valve, close the shutoff valve. When measurements are complete,
open the valve.
If there is not a shutoff valve in the line between the compressor discharge and
the hot gas bypass valve, disable the bypass by removing the cover from the
bypass valve and adjusting the spring tension. Count and record the number of
counterclockwise turns until the spring tension is relieved. (When ready to return
the bypass valve to its original setting, turn the spring the same number of turns
clockwise. To check setting, see instructions in Paragraph 3.9.5.)
IMPORTANT: Do not release refrigerant to the atmosphere! If
required service procedures include the adding or removing
of refrigerant, the qualified HVAC service technician must
comply with all federal, state or provincial, and local laws.