Application, Operation, & Maintenance Manual | DXM2 UNIT CONTROLS | Heat Controller, Inc. |
DXM2 Service & Application Notes
Pressure Switches
All pressure switches are designed to be normally closed during normal operating conditions, and to open upon fault.
Condensate Sensor – The Condensate Sensor input will fault upon sensing impedance less than 100,000 Ohms for 30 continuous seconds. The recommended design uses a single wire terminated with a male 1/4” quick connect located in the drain pan at desired trip level. Upon a high condensate level the water will short between the air coil and the quick connect producing a resistance less than 100,000 Ohms. Since condensate is free of impurities,
it has no conductivity. Only the impurities from the drain pan and coil dust or dirt create the conductance. A second ground wire with appropriate terminal to the drain pan can be used with the control to replace the air coil ground path. The Condensate Sensor can also essentially be any open contact that closes upon a fault condition.
Thermistor Temperature Sensors – The thermistors used with the DXM2 are NTC (negative temperature coefficient) type. Table 7 shows the replacement part numbers for the LT1 and LT2 thermistors. The sensors have a 1% tolerance and follow the characteristics shown in Table 8. Table 9 shows the nominal resistance at any given temperature and can be used for field service reference. The sensor will use a minimum of 24 awg wire.
Table 8: 1% Sensor Calibration Points
| Minimum | Maximum | Nominal |
Temp (°F) | Resistance | Resistance | Resistance |
| (Ohm) | (Ohm) | (Ohm) |
|
|
|
|
78.5 | 9523 | 9715 | 9619 |
|
|
|
|
77.5 | 9650 | 9843 | 9746 |
|
|
|
|
76.5 | 10035 | 10236 | 10135 |
|
|
|
|
75.5 | 10282 | 10489 | 10385 |
|
|
|
|
33.5 | 30975 | 31598 | 31285 |
|
|
|
|
32.5 | 31871 | 32512 | 32190 |
|
|
|
|
31.5 | 32653 | 33310 | 32980 |
|
|
|
|
30.5 | 33728 | 34406 | 34065 |
|
|
|
|
1.5 | 80624 | 82244 | 81430 |
|
|
|
|
0.5 | 83327 | 85002 | 84160 |
|
|
|
|
0.0 | 84564 | 86264 | 85410 |
|
|
|
|
Table 9: Nominal resistance at various temperatures
Temp (ºC) | Temp (ºF) | Resistance | Temp (ºC) | Temp (ºF) | Resistance | |
(kOhm) | (kOhm) | |||||
|
|
|
| |||
0.0 | 85.34 | 55 | 131.0 | 2.99 | ||
0.5 | 84.00 | 56 | 132.8 | 2.88 | ||
1.5 | 81.38 | 57 | 134.6 | 2.77 | ||
10.4 | 61.70 | 58 | 136.4 | 2.67 | ||
12.2 | 58.40 | 59 | 138.2 | 2.58 | ||
14.0 | 55.30 | 60 | 140.0 | 2.49 | ||
15.8 | 52.38 | 61 | 141.8 | 2.40 | ||
17.6 | 49.64 | 62 | 143.6 | 2.32 | ||
19.4 | 47.05 | 63 | 145.4 | 2.23 | ||
21.2 | 44.61 | 64 | 147.2 | 2.16 | ||
23.0 | 42.32 | 65 | 149.0 | 2.08 | ||
24.8 | 40.15 | 66 | 150.8 | 2.01 | ||
26.6 | 38.11 | 67 | 152.6 | 1.94 | ||
28.4 | 36.18 | 68 | 154.4 | 1.88 | ||
30.2 | 34.37 | 69 | 156.2 | 1.81 | ||
0 | 32.0 | 32.65 | 70 | 158.0 | 1.75 | |
1 | 33.8 | 31.03 | 71 | 159.8 | 1.69 | |
2 | 35.6 | 29.50 | 72 | 161.6 | 1.64 | |
3 | 37.4 | 28.05 | 73 | 163.4 | 1.58 | |
4 | 39.2 | 26.69 | 74 | 165.2 | 1.53 | |
5 | 41.0 | 25.39 | 75 | 167.0 | 1.48 | |
6 | 42.8 | 24.17 | 76 | 168.8 | 1.43 | |
7 | 44.6 | 23.02 | 77 | 170.6 | 1.39 | |
8 | 46.4 | 21.92 | 78 | 172.4 | 1.34 | |
9 | 48.2 | 20.88 | 79 | 174.2 | 1.30 | |
10 | 50.0 | 19.90 | 80 | 176.0 | 1.26 | |
11 | 51.8 | 18.97 | 81 | 177.8 | 1.22 | |
12 | 53.6 | 18.09 | 82 | 179.6 | 1.18 | |
13 | 55.4 | 17.26 | 83 | 181.4 | 1.14 | |
14 | 57.2 | 16.46 | 84 | 183.2 | 1.10 | |
15 | 59.0 | 15.71 | 85 | 185.0 | 1.07 | |
16 | 60.8 | 15.00 | 86 | 186.8 | 1.04 | |
17 | 62.6 | 14.32 | 87 | 188.6 | 1.01 | |
18 | 64.4 | 13.68 | 88 | 190.4 | 0.97 | |
19 | 66.2 | 13.07 | 89 | 192.2 | 0.94 | |
20 | 68.0 | 12.49 | 90 | 194.0 | 0.92 | |
21 | 69.8 | 11.94 | 91 | 195.8 | 0.89 | |
22 | 71.6 | 11.42 | 92 | 197.6 | 0.86 | |
23 | 73.4 | 10.92 | 93 | 199.4 | 0.84 | |
24 | 75.2 | 10.45 | 94 | 201.2 | 0.81 | |
25 | 77.0 | 10.00 | 95 | 203.0 | 0.79 | |
26 | 78.8 | 9.57 | 96 | 204.8 | 0.76 | |
27 | 80.6 | 9.16 | 97 | 206.6 | 0.74 | |
28 | 82.4 | 8.78 | 98 | 208.4 | 0.72 | |
29 | 84.2 | 8.41 | 99 | 210.2 | 0.70 | |
30 | 86.0 | 8.06 | 100 | 212.0 | 0.68 | |
31 | 87.8 | 7.72 | 101 | 213.8 | 0.66 | |
32 | 89.6 | 7.40 | 102 | 215.6 | 0.64 | |
33 | 91.4 | 7.10 | 103 | 217.4 | 0.62 | |
34 | 93.2 | 6.81 | 104 | 219.2 | 0.60 | |
35 | 95.0 | 6.53 | 105 | 221.0 | 0.59 | |
36 | 96.8 | 6.27 | 106 | 222.8 | 0.57 | |
37 | 98.6 | 6.01 | 107 | 224.6 | 0.55 | |
38 | 100.4 | 5.77 | 108 | 226.4 | 0.54 | |
39 | 102.2 | 5.54 | 109 | 228.2 | 0.52 | |
40 | 104.0 | 5.33 | 110 | 230.0 | 0.51 | |
41 | 105.8 | 5.12 | 111 | 231.8 | 0.50 | |
42 | 107.6 | 4.92 | 112 | 233.6 | 0.48 | |
43 | 109.4 | 4.72 | 113 | 235.4 | 0.47 | |
44 | 111.2 | 4.54 | 114 | 237.2 | 0.46 | |
45 | 113.0 | 4.37 | 115 | 239.0 | 0.44 | |
46 | 114.8 | 4.20 | 116 | 240.8 | 0.43 | |
47 | 116.6 | 4.04 | 117 | 242.6 | 0.42 | |
48 | 118.4 | 3.89 | 118 | 244.4 | 0.41 | |
49 | 120.2 | 3.74 | 119 | 246.2 | 0.40 | |
50 | 122.0 | 3.60 | 120 | 248.0 | 0.39 | |
51 | 123.8 | 3.47 | 121 | 249.8 | 0.38 | |
52 | 125.6 | 3.34 | 122 | 251.6 | 0.37 | |
53 | 127.4 | 3.22 | 123 | 253.4 | 0.36 | |
54 | 129.2 | 3.10 |
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