Installation, Operation and Maintenance Manual
C13-Series
23
Subject to change without notice.
10.20-IM (0818)
Hot Water Coils
The hot water coil is located in the return air� The coil is
copper tube/aluminum fin. Connections exit the cabinet at
the coil location� Controls and valves for hot water coils are
supplied by others�
Flooded Condenser
When the outdoor ambient temperature falls, the condensing
pressure falls� This causes the discharge pressure to fall�
Since the pressure differential across the thermostatic
expansion valve port affects the rate of refrigerant flow, low
discharge pressure generally causes insufficient refrigerant
to be fed to the evaporator. Failure to have sufficient head
pressure will result in low suction pressure and/or iced
evaporator coils� The effective range for this option is down
to -30°F�
The purpose of a flooded condenser is to hold back enough
of the condensed liquid refrigerant so that some of the
condenser surface is rendered inactive� This reduction of
active condensing surface results in a rise in condensing
pressure and sufficient liquid line pressure for normal system
operation�
A three-way modulating valve and a receiver make up the
flooded condenser refrigerant components.
The valve is placed in the liquid line after the condenser�
The receiver is downstream of the valve� The valve limits
the flow of liquid refrigerant from the condenser while at the
same time regulating the flow of discharge gas around the
condenser to the receiver�
During periods of low ambient operation, the receiver
pressure falls until it approaches the setting of the control
point of the valve (typically 295 PSIG for R-410a)� The valve
then throttles to restrict the flow of liquid from the condenser.
This raises the condenser pressure� Since it is the receiver
pressure that is being maintained, the valve will then start
to throttle open the discharge port when the differential
between the condensing pressure and the receiver pressure
exceeds 20 psi� The hot discharge gas serves to heat up the
cold liquid being passed from the condenser to the receiver�
Thus the liquid reaches the receiver warm and with sufficient
pressure to assure proper expansion valve operation�
The receiver is required to hold all of the excess/ additional
liquid refrigerant in the system, since the refrigerant will be
returned to the receiver when high ambient conditions exist�
In the off-cycle the refrigerant can “migrate” to the condenser,
during periods of low outdoor ambient� On a call for start-
up, the evaporator pressure may not build up to the cut-in
point of the low pressure control� The result may be a failure
of the compressor to start or to short cycle� To eliminate
this potential problem, a time delay is added to bypass the
low pressure switch during start-up to allow the discharge
pressure to build in turn increasing the suction pressure�
Buck/Boost Transformer
Table 5: Buck/Boost Transformer Table
United CoolAir
Part Number
LOAD
Max. Size of
Fuse or Breaker
4CA1901
KVA
1.44
10A
Amps
6.25
4CA1902
KVA
2.88
15A
Amps
12.5
4CA1903
KVA
4.31
20A
Amps
18.75
4CA1904
KVA
5.75
30A
Amps
25.0
4CA1905
KVA
8.63
40A
Amps
37.5
4CA1906
KVA
11.5
60A
Amps
50.0
4CA1907
KVA
17.25
80A
Amps
75.0
Single-Phase
Figure 14: Transformer Wiring
Units being applied on a 277V-1PH-60Hz power supply
require the use of a buck/boost transformer� The transformer
will reduce the voltage from 277-1-60 to 230-1-60� The unit
is supplied with components for 230-1-60 application� Table
1 lists the buck/boost transformers available from United
CoolAir� Figure 16 illustrates the wiring for each transformer�
INPUT
OUTPUT
H4 H3
H2 H1
X4 X3 X2 X1
Summary of Contents for C13-Series
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