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
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