Table 5.
R-410A refrigerant pressure/temperature
settings
R-410A Refrigerant Pressure/Temperature Settings
Normal
Min.
Max.
Sub-cooling °F
10
5
20
Superheat °F
15
10
20
Design Condensing
Temp. @ 95°F Ambient
125
105
140
Suction Pressure
(psig)-
130
105
155
Installation
SS-SVX002B-EN
35
Saturated Refrigerant Pressure
The following refrigerant temperature/pressure table is
provided for reference for R-410A refrigerant.
Table 6.
R-410A refrigerant pressures
Temp. (°F)
Pressure
(psig)
Temp. (°F)
Pressure
(psig)
20
78.4
75
218
22
81.9
80
236
24
85.5
85
255
26
89.2
90
274
28
93.1
95
295
30
97
100
318
32
101
105
341
34
105
110
365
36
109
115
391
38
114
120
418
40
118
125
446
42
123
130
477
44
128
135
508
46
133
140
541
48
137
50
143
55
155
60
170
65
185
70
201
Settings and Adjustments
Low/High Pressure Limit Switch
Air conditioning systems utilizing DX refrigerant are
equipped with hermetically sealed high-pressure and low-
pressure switches. These switches are pre-set by the
manufacturer and cannot be adjusted. The high- pressure
switch opens at 630 psig and has a manual reset. The low-
pressure switch opens at 65 psig (± 10) and closes at 105
psig (± 10) and has an automatic reset.
Head Pressure Controls- Air Cooled
Systems
-20°F Condenser Fan Speed
Used for outdoor installations where ambient condenser
air inlet temperatures may fall to -20°F, variable speed
condenser motor control is used to maintain head
pressure. The variable speed motor is located closest to
the header end of the condenser.
The fan speed control is a continual modulation of the
motor’s speed. The condenser fan speed controller is
factory installed in the remote outdoor condenser electric
box. The fan speed controller requires no adjustment.
Wire the condenser in accordance with the electrical
schematic and appropriate codes. The fan speed controller
will automatically control the head pressure. On systems
with more than one fan on the condenser, the remaining
motors cycle on and off based on pressure.
Factory setting: Switch contacts are set to close on a
pressure rise to 440 psig and open at 330 psig. Set point
range is 200 to 610 psig. The differential is set at 110 psi and
is adjustable.
-30°F Flooded Head Pressure Control
Used for outdoor or indoor installations where ambient
condenser air inlet temperatures may fall to -30°F, flooded
head pressure control is designed to maintain head
pressure during low ambient conditions. A head pressure
control valve and a receiver is used in the refrigeration
circuit to back up liquid refrigerant into the condenser coil.
The head pressure control valve is a 3-way modulating
valve controlled by discharge pressure.
When the A/C unit begins to operate, the discharge
pressure rises to 320 psig and the condenser fan is cycled
on, as described in
“-20°F Condenser Fan Speed,” p. 35
When ambient temperature drops, the discharge pressure
drops also. When the discharge pressure drops, the head
pressure control valve diverts discharge gas away from
the condenser to the receiver. Liquid flow from the
condenser is restricted, causing liquid to back up in the
condenser.
Flooding the condenser reduces the area available for heat
transfer. The desired result is to increase the pressure into
the condenser, maintaining a minimum discharge
pressure during low ambient operation thus ensuring
proper condensing temperature. The head pressure
control valve requires no adjustment.
While the fan is running, the flooded head pressure control
valve modulates the amount of discharge gas entering the
receiver. As the pressure increases, the valve diverts more
discharge gas to the condenser, allowing more liquid to
flow from the condenser to the receiver.
When using this method of head pressure regulation there
must be enough refrigerant in the system to ensure
adequate charge at the lowest expected ambient
temperature in which the system will be operating. A
