40
FORM 145.32-IOM5
ISSUE DATE: 04/08/2019
SECTION 2 – STARTUP AND OPERATION
Superheat
Only check superheat after establishing the steady state
operation of the unit, pulling down the discharge air tem-
perature to within the control range, and running the unit
in a fully loaded condition.
The superheat is calculated as the difference between
the actual temperature of the refrigerant gas in the suc-
tion line and the temperature corresponding to the suc-
tion pressure as shown in
For example, when the suction pressure is 130 psig and
the suction line temperature is 57.0°F:
• Saturation Temperature for 130 psig = 45.0°F
• Evaporator Superheat = Suction Line Temperature
(57.0°F) minus Saturation Temperature (45.0°F)
= 12.0°F
When adjusting the expansion valve, do not turn the
adjusting screw more than one turn at a time This al-
lows sufficient time (approximately 15 minutes) be-
tween adjustments for the system and the thermal ex-
pansion valve to respond and stabilize.
The superheat setting should be adjusted to 8.0–11.0°F
at design conditions.
Leak Checking
Leak check compressors, fittings, and piping to ensure
there are no leaks. Verify the evaporator distributor
tubes do not have bare copper touching each other or
are against a sheet metal edge. If leak checking a unit
charged with R-410A, ensure the leak test device is ca-
pable of sensing refrigerant R-410A.
Startup (Cooling)
Prestart Checklist
After installation has been completed, make the fol-
lowing checks:
1. Check the electrical supply voltage. Ensure that it
is the same as listed on the unit nameplate.
2. Set the room thermostat to the OFF position.
3. Turn ON the unit electrical power.
4. Set the room thermostat fan switch to ON.
5. Check the indoor blower rotation.
6. Check the blower drive belt tension.
7. Check the unit's supply air (CFM).
• Liquid Line Subcooling = Saturation Temperature
(108.0°F) minus Liquid Line Temperature (95.0°)
= 13.0°F
Subcooling should be 10.0–14.0°F at design conditions.
TABLE 25 -
R-410A PRESSURE AND TEMPERA-
TURE CHART
PSIG
TEMP ˚F
PSIG
TEMP ˚F
0
-60
78
20
2
-58
80
21
4
-54
85
24
6
-50
90
26
8
-46
95
29
10
-42
100
32
12
-39
105
34
14
-36
110
36
16
-33
115
39
18
-30
120
41
20
-28
125
43
22
-26
130
45
24
-24
135
47
26
-20
140
49
28
-18
145
51
30
-16
150
53
32
-14
160
57
34
-12
170
60
36
-10
180
64
38
-8
190
67
40
-6
200
70
42
-4
210
73
44
-3
220
76
46
-2
225
78
48
0
235
80
50
1
245
83
52
3
255
85
54
4
265
88
56
6
275
90
58
7
285
92
60
8
295
95
62
10
305
97
64
11
325
101
66
13
355
108
68
14
375
112
70
15
405
118
72
16
500
134
74
17
600
149
76
19
700
159
