Lochinvar 502 - 2072 Checking temperature sensors, Resistance Temperature, Temperature Resistance

Copper-fin II/IIE Boiler, Water Heater and Pool Service Manual

3 Troubleshooting (continued)

Checking temperature sensors

The appliance temperature sensors (inlet water, outlet water, system water, tank water, flue, and outdoor air) are all resistance type devices. The following tables show the correct values for the sensors at various temperatures. Use an ohmmeter to read the resistance of the sensor at a known temperature. If the resistance of the sensor does not closely match its corresponding table, replace the sensor.

Table 3B Inlet/Outlet/System/Tank Sensor Resistance vs. Temperature

	S1a				S1b
	(Wire Color - W and Y)				(Wire Color - W/Y and Y)
Temperature	Resistance	Temperature	Resistance	Temperature	Resistance	Temperature	Resistance
50	19,553	158	2,004	50	40,030	158	3,478
68	12,690	176	1,464	68	25,030	176	2,492
86	8,406	194	1,084	86	16,090	194	1,816
104	5,715	212	816	104	10,610	212	1,344
122	3,958			122	7,166
140	2,786			140	4,943

Table 3C Outdoor Air Sensor Resistance vs. Temperature

Temperature	Resistance	Temperature	Resistance
-50	490,813	20	46,218
-40	336,606	30	34,558
-30	234,196	40	26,099
-20	165,180	50	19,900
-10	118,018	60	15,311
0	85,362	70	11,883
10	62,465	80	9,299

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