Reznor MASA Unit Installation Manual - Manual (Page 22)

Form I-COND, P/N 220746R6, Page 22
8.3 Other Compressor and Refrigerant Controls
Check the wiring diagram on the unit to determine if it has optional controls.
8.3.1 High Pressure Cutoff
The high pressure cutoff control is located in the discharge line as it exits the
compressor. If the discharge pressure exceeds the high pressure cutoff setting
(600±15psi), the control will stop compressor and condenser fan operation.
The high pressure cutoff control is a manual reset device. It can be reset when
the pressure drops below the differential setting (400 ±15psi). Correct the prob-
lem before resetting the device to restart operation of the system.
8.3.2 Low Pressure Cutoff
The low pressure cutoff control is located in the suction line as it enters the
compressor. If the suction pressure drops below the low pressure cutoff setting
(35±5psi), the control will stop compressor and condenser fan operation. The
low pressure cutoff control will automatically restart operation when the suction
pressure goes above 50±5psi.
8.3.3 Hot Gas Bypass Valve (Option CUG2 or CUG3)
If ordered with Option CUG 2 or 3, the bypass valve will provide expanded
compressor modulation at low outside air temperatures by allowing some of
the gas from the discharge line to be re-routed directly to the evaporator coil.
Option CUG2 has a hot gas bypass on one circuit. Option CUG3 has a hot gas
bypass on both circuits.
The hot gas bypass valve is factory set. However, the factory setting should
be checked at startup. To check the valve operation and/or make field adjust-
ments, it is necessary to simulate a light load condition as described below.
Check Hot Gas Bypass Valve Setting - Connect a pressure gauge to the suc-
tion line and block the entering air to the evaporator coil. Suction pressure will
drop, and the hot gas bypass valve should begin to open at approximately 115
psi and will be fully open at 95 psi. When the valve begins to open, it will be hot
to the touch (see caution below).
CAUTION
Touching the operating hot gas bypass valve can cause a
burn. Use caution when checking and adjusting the valve.
See Hazard Levels, page 3.
If pressure needs to be adjusted, remove the cap and turn the adjusting stem
clockwise to increase the pressure setting or counterclockwise to decrease the
pressure setting. Make adjustments in small increments. Allow five minutes
between adjustments for the system to stabilize. When finished, replace the
cap on the adjustment stem and remove the pressure gauge.
8.3.4 Compressor Protection (Option CUB1)
If ordered with Option CUB1, the condensing unit has a five-minute anti-short
cycle timer on compressor operation.
NOTE: Standard with Reznor PreevA
® with digital FX05 controls.
8.3.5 Crankcase Heaters
Each scroll compressor in the condensing unit has a band-type crankcase
heater. Crankcase heaters must always have been energized for at least 24
hours prior to operating the compressor.
8.0 Controls and
Operation
(cont’d)