McQuay IM 937 43
System Check, Test, and Start
R-407C leaks
R-407C is a zeotropic blend of three HFC refrigerants (R-32,
R-125, and R134a). Zeotropic blends do not behave as one
substance. Therefore, a change of phase does not occur at a
fixed temperature. R-407C has a “glide” of 8°F because it
boils and evaporates over a 8°F change in temperature.
If an R-407C unit leaks refrigerant, there is no way to
determine how much of each of the three component
refrigerants has leaked. However, experience in the field
shows that R-407C can be “topped” off after a leak and operate
normally. There is no need, except in the case of critically
charged systems, to replace the entire charge after a leak.
When recharging or topping off a system using R-407C, it is
important to remove the refrigerant from the charging cylinder
in the liquid phase. Many of the cylinders for the newer
refrigerants use a dip tube so that in the upright position, liquid
is drawn from the cylinder. DO NOT vapor charge out of a
cylinder unless the entire cylinder is to be charged into the
system. Refer to charging instructions provided by the
refrigerant manufacturer.
Figure 41: Water and Refrigerant Piping Schematic
Variable Air Volume (VAV) Start-Up
Enter the duct static pressure set point value and parameters
through the keypad:
SAF Spd Control
DuctSP Spt=
When the appropriate number of VAV terminal boxes are
opened by setting down their respective thermostats, the VFD
should go to the maximum airflow. Upon closing enough VAV
boxes by setting their respective thermostats up, the inlet VFD
should go to the minimum airflow position.
RPM Changes
All units are provided with fixed pitch sheaves selected for the
specified operating conditions. If a new fan rpm selection is
required, field install a new sheave selection. Adjust the belt
tension as described below.
CAUTION
Adding refrigerant to the suction must always be done by
trained service personnel that are experienced with the risks
associated with liquid-related damage to the compressor.
RELIEF
VALVE
ISOLATION
VALVE
FILTER
DRIER
SIGHT
GLASS
ISOLATION
VALVE
EXPANSION
VALVE
SUCTION
VALVE
DISCHARGE
VALVE
COMPRESSOR NO. 1
CONDENSER
RECEIVER
EQUALIZER
CAPILLARY
EVAPORATOR
A- A
RELIEF
VALVE
ISOLATION
VALVE
FILTER
DRIER
SIGHT
GLASS
ISOLATION
VALVE
EXPANSION
VALVE
SUCTION
VALVE
DISCHARGE
VALVE
COMPRESSOR NO. .2
CONDENSER
RECEIVER
EQUALIZER
CAPILLARY
EVAPORATOR
A- A
RELIEF
VALVE
ISOLATION
VALVE
FILTER
DRIER
SIGHT
GLASS
ISOLATION
VALVE
EXPANSION
VALVE
SUCTION
VALVE
DISCHARGE
VALVE
COMPRESSOR NO. 3
CONDENSER
RECEIVER
EQUALIZER
CAPILLARY
EVAPORATOR
A- A
RELIEF
VALVE
ISOLATION
VALVE
FILTER
DRIER
SIGHT
GLASS
ISOLATION
VALVE
EXPANSION
VALVE
SUCTION
VALVE
DISCHARGE
VALVE
COMPRESSOR NO. 4
CONDENSER
RECEIVER
EQUALIZER
CAPILLARY
EVAPORATOR
A- A
MODERATING
VALVE
WATER FLOW SWITCH
BYPASS
VALVE
WATER SENSORS
LOW
HIGH
E.S.
WATER
COIL
CONDENSER
WATER
OUT
CONDENSER
WATER
IN
SUCTION
LINE
EXPANSION
VALVE
BULB
CAPILLARY
12'
SECTION A - A
30°
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