Table 11 — Sensor Resistance Values
TEMP
(F)
RESISTANCE
(Ohms)
TEMP
(F)
RESISTANCE
(Ohms)
TEMP
(F)
RESISTANCE
(Ohms)
−60
362,640
45
11,396
150
1,020
−55
297,140
50
9,950
155
929
−50
245,245
55
8,709
160
844
−45
202,841
60
7,642
165
768
−40
168,250
65
6,749
170
699
−35
139,960
70
5,944
175
640
−30
116,820
75
5,249
180
585
−25
98,420
80
4,644
185
535
−20
82,665
85
4,134
190
490
−15
69,685
90
3,671
195
449
−10
58,915
95
3,265
200
414
−5
50,284
100
2,913
205
380
0
42,765
105
2,600
210
350
5
36,475
110
2,336
215
323
10
31,216
115
2,092
220
299
15
26,786
120
1,879
225
276
20
23,164
125
1,689
230
255
25
19,978
130
1,527
235
236
30
17,276
135
1,377
240
219
35
14,980
140
1,244
40
13,085
145
1,126
3. Quick Test Steps 2.4.-3.3. — Output Relays
These quick test steps allow microprocessor to check
output signals from relay boards in unit control system. In ad-
dition, operation of all the condenser fans, compres-
sors, and economizer (if equipped) are checked at each step.
Normal display for Steps 2.4. through 2.8. is 1. In Steps
2.9. through 3.2., each compressor and unloader is started
and allowed to run for approximately 10 seconds. At start-
up, a 0 will appear on the display followed by a 1 (Steps
2.9. and 3.2.) in a few seconds. Steps 3.0. and 3.1. will
always be 0 since there are unloaders, and Step 3.3. will
always be zero since it is not used.
At end of the 10-second time period, a 0 will return to the
display board indicating that test step has been success-
fully completed (Steps 2.9. and 3.2.). The 1 indicates that
was tested.
Fan and compressor operating sequence for quick test
Steps 2.4. through 3.3. are shown in Table 10.
If the quick test steps do not operate as described above,a
defect exists in one or more of the following: relay being
tested, electronic control, or unit wiring. Determine problem
and correct.
SERVICE AND TROUBLESHOOTING
NOTE: The service and troubleshooting instructions in this
section apply specifically to VAV rooftop units. For infor-
mation regarding service and troubleshooting which is com-
mon to all 20 to 75 ton rooftop units, refer to base unit in-
stallation instruction literature.
Inlet Guide Vane Motor (Units with Inlet Guide
Vanes and Static Pressure Control Option) —
The inlet guide vane motor is located next to the evaporator
fan. Access is through the 2 doors labeled FAN SECTION
on the left side of the unit (024-030) or on both sides of the
unit (034-074). See Fig. 26-29 for location of the inlet guide
vane damper motor.
Modulating Power Exhaust Differential Pres-
sure Switch
SIZE 024-030 UNITS — The modulating power exhaust dif-
ferential pressure switch is located in the small control box
mounted on the corner post next to the access door labeled
FILTER SECTION. See Fig. 30. To gain access to this box,
remove the small control box cover. When replacing cover,
be sure to properly secure it in order to prevent water from
being drawn into the unit.
This box also contains a pressure gage and a 24-v trans-
former for powering the modulating power exhaust damper
motor.
SIZE 034,044 UNITS — The modulating power exhaust dif-
ferential pressure switch is located in the auxiliary control
box mounted in the corner next to the power exhaust motor
door. To gain access to this control box, remove the auxil-
iary control box cover. When replacing cover, be sure to prop-
erly secure it in order to prevent water from being drawn
into the unit. See Fig. 28 and 29.
SIZE 054-074 UNITS — The modulating power exhaust dif-
ferential pressure switch is mounted below the auxiliary con-
trol box next to the access door labeled FILTER SECTION.
See Fig. 28 and 29.
Inlet Guide Vane Differential Pressure Switch
(Units with Inlet Guide Vane and Static Pres-
sure Control Option)
SIZE 024-030 UNITS — On the 50DK units, the inlet guide
vane motor differential pressure switch is located on the post
on the right-hand side of the blower assembly (when facing
the blower assembly). Access is through the access door la-
beled FAN SECTION. This access door is right next to the
access door to the main unit control box. See Fig. 26.
Fig. 26 — Location of Differential Pressure Switch
and Inlet Guide Vane Motor (50DK024-030 Units)
Fig. 27 — Location of Differential Pressure Switch
and Inlet Guide Vane Motor (48DK/50DY024-030 Units)
21
