BY GEORGE LANTHIER
Figure 12
proper meter lead terminals , 20A and COM for amps or mA and COM for the measurement of milliamps or microamps and that DC appears in the display . If not , push on the RANGE button .
Do not touch the metal tips while testing and remember that in amperage testing , we must be in series with the circuit . By using the mA function of the meter , you can check the battery charge measurement of most batteries found on HVAC equipment .
This test should not be used for anything other than 1.5 Vdc and 9 Vdc batteries . Make
Figure 13
sure the leads are connected properly and set the meter for the mA scale . Connect the red probe to the positive (+) side of the battery and the black lead to the negative ( - ) side of the battery . The normal amperage for 1.5 volt ‘ AA ’ ( LR6 ) batteries should be 4 mA and 9-volt ( 6LR61 ) batteries should be 25 mA .
The measurement of DC microamps is important on many of today ’ s modern gas systems that use an ignition control module , Figure 8 . In Figure 9 we show the use of a multimeter equipped with a µ Adc scale to measure the current flow between ground and the ‘ Burner Ground ’ connection on a Honeywell S8610U ignition control module . The DM3218 , Figure 2 , can also be used in a test lead configuration to measure this amperage .
DC microamps µ Adc testing may also be required to evaluate flame signal on many gasburners . OEM directions should always be consulted . Here is a test procedure for a Honeywell S87 module , Figure 10 , with a Q354 flame detector , Figure 11 . Note that not all necessary components and wiring are shown for clarity in Figure 12 . This is a tworod system , the procedure for a single Hot Surface Ignition ( HSI ) system follows .
TWO-ROD SYSTEM - FLAME SENSOR CIRCUIT
The S87 provides ac power to the igniter / sensor ( on S87A , B and J ) or the flame sensor ( on S87C , D and K ) which the burner flame rectifies to direct current . If the flame signal back to the S87 is less than 1.5 µ Adc , the system will lock out .
The output of the flame sensing circuit cannot be checked directly on the S87 . Check the flame sensing circuit directly by checking the flame sensing current from the sensor to
Figure 14
the S87 as follows .
Connect a meter ( DC microammeter scale ) in series with the flame signal ground wire as shown in Figure 13 . Use the 81B or equivalent . Disconnect the ground wire at the S87 . Connect the red ( positive ) meter lead to the free end of the ground wire .
Connect the black ( negative ) meter lead to the quick-connect ground terminal on the S87 .
Figure 15
Restart the system and read the meter . The flame sensor current must be at least 1.5 µ Adc and steady . If the reading is less than 1.5 µ Adc or unsteady , see LOW OR UNSTEADY FLAME CURRENT .
40 JULY 2023 | FUEL OIL NEWS | www . fueloilnews . com