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Electromechanical Economizer Testing
Electromechanical Mixed Air Sensor
When the outdoor air thermostat is in the cold position (closed), the unit will attempt to economize
if a fan (G) and cooling (Y1) call exists at the ECA module. This is readily apparent at the ECA, as
the "OK to economize" LED will be on. During this time, the ECA is measuring the Mixed Air
temperature via the Mixed Air Sensor (MAS).
Service Tips
The MAS sensor is not energized unless the LED is on (G signal present, OK to economize), and the
Y1 signal is present.
If the MAS is open, approximately 4.3 VDC will be seen.
Outdoor Air Thermostat opens at 70°F and closes at 60°F .
Read the voltage with the sensor connected, read the resistance with the sensor disconnected.
Table 42. Temperature Input
Temp F
33.8
35.6
37.4
39.2
41.0
42.8
44.6
46.4
48.2
50.0
51.8
53.6
55.4
57.2
59.0
60.8
62.6
64.4
66.2
68.0
69.8
71.6
73.4
75.2
77.0
78.8
80.6
82.4
84.2
86.0
87.8
114
Temp C
R(K OHMS)
DC Volts Temp F
1
9.576
3.910
2
9.092
3.882
3
8.636
3.894
4
8.204
3.863
5
7.796
3.829
6
7.412
3.790
7
7.048
3.749
8
6.705
3.713
9
6.380
3.674
10
6.073
3.634
11
5.782
3.590
12
5.507
3.550
13
5.247
3.507
14
5.000
3.420
15
4.767
3.373
16
4.545
3.328
17
4.335
3.283
18
4.136
3.239
19
3.948
3.180
20
3.769
3.157
21
3.599
3.118
22
3.437
3.080
23
3.284
3.034
24
3.138
3.007
25
3.000
2.971
26
2.869
2.932
27
2.744
2.896
28
2.625
2.860
29
2.512
2.824
30
2.404
2.787
31
2.301
2.750
Temp C
R(K OHMS)
89.6
32
2.204
91.4
33
2.111
93.2
34
2.023
95.0
35
1.938
96.8
36
1.858
98.6
37
1.781
100.4
38
1.708
DC Volts
2.714
2.676
2.639
2.600
2.561
2.526
2.484
RT-SVD03G-EN
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Troubleshooting
