AAF HermanNelson IM 725 Installation Manual - page 25
IM 725 (1-02)
25
Table 18 —Saturated Temperature - Pressure Chart
(°F)
R22-PSIG
(°F)
R22-PSIG
(°F)
R22-PSIG
32
57.5
44
74.5
80
143.6
33
58.8
45
76.0
85
155.7
34
60.1
46
77.6
90
168.4
35
61.5
47
79.2
95
181.8
36
62.8
48
80.8
100
195.8
37
64.2
49
82.4
105
210.8
38
65.6
50
84.0
110
226.4
39
67.1
55
92.6
115
242.7
40
68.5
60
101.6
120
259.9
41
70.0
65
111.2
125
277.9
42
71.4
70
121.4
130
296.8
43
73.0
75
132.2
140
337.3
Determining System Superheat
After the subcooling has been determined, check system superheat.
1. Determine required superheat from superheat range, table 18.
2. Measure suction line temperature 6 inches from service valve.
3. Measure suction line pressure at service valve and determine
saturated suction temperature from table 18.
4. Subtract saturated suction temperature from measured temperature
to obtain superheat.
5. Refer to table 19 and adjust charge as required for correct superheat
at ambient conditons.
Note:
Each time that charge is added or removed from the system, allow the system to
run approximately 20 - 30 minutes before pressure and temperature readings are
taken and superheat calculations made.
Note:
If system hunting occurs or subcooling is reduced, it may be necessary to adjust
TXV to obtain correct superheat.
Filter(s)
With AAF-HermanNelson’s single-filter design, filter changeout
takes only seconds.
Turn off the unit, (fan speed switch or unit on/off switch is located
behind the right front end compartment panel). Remove the center
front panel, pull out the filter and replace with a clean filter. Replace
the center panel and restart the unit.
Filters should be replaced during the first week of placing into service
to prevent dirt carry-over into the internals of the unit and back into the
classroom, (see figure 81). A periodic filter changeout program should
be established. Filters are included in all units. AAF
®
-HermanNelson
®
single-use filters are standard on all but electric heat units, which come
with permanent wire mesh filters. Permanent wire mesh and renewable
media filters are available for non-electric heat units, in lieu of
single-use filters.
•
Single-use filters feature Amerglas media. They are designed to
be used once and discarded.
•
Permanent filters are metal filters that may be removed for
cleaning and reused numerous times.
•
Renewable media filters (figure 81) consist of a heavy painted
metal structural frame and renewable Amerglas media
12" Left Front
Access Panel
Filter
Motor
12" Right Front Access Panel
Renewable Media (Single-use And
Permanent Wire Mesh Filters Also Available.)
Structural
Frame
Top Access
Doors
Figure 81 - Filter installation
Superheat Adjustment
1. Remove the seal cap from thermal expansion valve (see figure 80).
2. Turn the adjustment screw clockwise to increase superheat and
counterclockwise to decrease superheat (see figure 80). One
complete 360° turn changes the superheat approximately 3-4°F,
regardless of the refrigerant type. As much as 30 minutes may be
required for the system to stabilize after the adjustment is made.
3. Replace and hand-tighten seal cap.
Figure 80- Superheat Adjustment of TXV
Superheat
Adjustment Screw
Counterclockwise To
Decrese Superheat
Clockwise To Increse
Superheat
CAUTION
!
Remove Seal Cap
Do not force adjustment stem of TXV. When adjusting superheat
setting, there are a maximum of 10 turns on the stem. Turning
adjustment stem after reaching stop will damage valve.
Outdoor
Indoor Coil Air Inlet Temp.
Ambient
DB/WB (50% RH)
75/63
80/67
85/71
105
*
*
8-10
100
*
3-5
9-11
95
*
5-7
11-13
90
*
9-11
13-15
85
5-7
10-12
15-17
80
8-10
12-14
18-20
75
10-12
15-17
21-23
70
13-15
19-21
24-26
65
15-17
21-23
26-28
Table 19 —Superheat Range
CAUTION
!
TURN OFF UNIT BEFORE SERVICING
CAUTION
!
Units must have a filter installed when operating.