Fuel Oil News

Fuel Oil News - January 2017

The home heating oil industry has a long and proud history, and Fuel Oil News has been there supporting it since 1935. It is an industry that has faced many challenges during that time. In its 77th year, Fuel Oil News is doing more than just holding

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Page 43 of 51

44 JANUARY 2017 | FUEL OIL NEWS | www.fueloilnews.com BY GEORGE LANTHIER HVAC/ HYDRONICS THIS IS TAKEN FROM OUR BOOKS "WIRING Fuel Burning Equipment, Book Two, Meters and Testers" and "Book Five, Hot Water Systems". It applies to both gas and oil systems. On oil 24 volts is mostly used for control, on gas 24 volts may be the life voltage of the system. We're going to review 24 volt trans- formers and a few other things too! Let's start by checking the voltages and that the transformer is "in phase". Check that the transformer is properly "phased". With your voltmeter verify that 120 volts (Vac) is present on the primary side of the transformer, Figure 1. Then, measure that the 24 Vac is present, Figure 2. Recheck the primary terminals. LINE VOLTAGE (120 VAC): 1. Between L1-HOT (black) and ground you should read 120 volts (Vac). 2. Between L1 and L2-NEUTRAL (white) you should read 120 volts (Vac). 3. Next check between L2 and ground (green) you should get zero volts (0 Vac). If you read 120 Vac between neutral and ground the polarity of the transformer is incorrect. If you mea- sure any voltage between neutral and ground that indicates a bad ground. It is essential for proper operation that a good ground is present. Most check this with furnaces, but assume that the ground will be present with boilers and water heaters and in many cases are wrong. LOW VOLTAGE (24VAC): Measure between L1 (black) and the power output of the second- ary (typically R). If you read 96 volts (Vac) then the transformer is properly in phase. If you read 144 volts (Vac) then the transformer is not properly phased. Swap the two secondary leads to put the transformer in phase. Never check the voltage by shorting the two output (secondary) windings with a screwdriver! Many newer transformers are now made with internal fuses and by shorting them that spark you see may be the death of the transformer since the fuse is not replace- able. Let's check a gas ignition module next. POWER CHECK. 1. Perform normal system checks of main power, 120 Vac and transformer, 24 Vac. With power on and the thermostat calling for heat, check the voltage at the "24 V" or "TH" to the 24 Vac ground at the module or integrated control, Figure 3. If 24 Vac is not pres- ent at the transformer, check other controls in the circuit from the transformer to the module or integrated control. 2. Check for 120 Vac across L1 (hot) and L2 (neutral). Check for 120 Vac from 'IGN' to 'IGN'. On some ignition modules also check the Hot Surface Ignitor (HSI) terminals for 120 Vac or 24 Vac depending on the control type. If you have 24 Vac or 120 Vac to the module or integrated control, and no 120 Vac or 24 Vac out of the module or integrated control, the module or control is faulty. 3. Check the ground. Test and re-verify that you have 120 Vac between your HOT (L1) and Neutral (L2). Then test L1 to ground, you should read 120 volts (Vac). Then test L2 to ground, you should read zero volts (Vac). If any voltage can be measured between L2 and ground, you have a bad ground. A green ground wire may need to be wired back to the main electrical board. This BRN/GND 24 GND MV 24 V METER TEST JACKETS IGNITION TRIAL SELECTOR DIP SWITCH HOT SURFACE IGNITER MV SENSE JUMPER WIRE SENSE LOW VOLTAGE Figure 1 Figure 2 Figure 3

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