6.8.2 Troubleshooting the 24 VAC Circuit in FBR18 Units
UNIT IS CONNECTED TO
POWER SUPPLY, DRAIN VALVE IS FULLY CLOSED, CONTROLLER IS ON AND IS CALLING FOR HEAT (decimal appears between first
two digits in controller display).
Is 24VAC present on
interface board J3 pin 9 Yes (LED 5 (GV) lit)?
No
NOTE: All voltage measurements must be made within 4 seconds of unit calling for heat. If unit does not fire within 4 seconds, ignition modules will lock out and controller must be turned off then back on to reset.
Is 24VAC |
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present across the gas | Yes | 24V circuit is |
valve main coil (PV |
| OK. |
terminal)? |
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No |
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Probable cause is |
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failed wire between |
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interface board and gas |
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valve. |
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Is LED 3 (24V) lit |
| Probable causes are failed |
|
No | 24V transformer or failed |
| |
continuously? |
| wiring between transformer | |
|
| and interface board. |
|
Yes |
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Is LED 4 | Yes | Is LED 2 | Yes |
(PWR) lit? |
| (PWR) lit? |
|
No |
| No |
|
Check for 12VDC across interface |
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| |
board J2 pins 4 & 5 when controller is calling |
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| |
for heat. If 12VDC is not present, probable | Is 24VAC |
| |
causes are failed controller or failed relay on | present on 25V terminal | Yes | |
interface board. On later design boards, relay K3 | of RIGHT ignition |
| |
may be replaced. On earlier design boards, | module? |
| |
the entire interface board must be |
|
| |
replaced..
No
Probable causes are failed
wiring between blower centrifugal switch and module, failed centrifugal switch, or failed wiring harness.
Is 24VAC |
|
| |
present on 25V terminal | No |
| |
of LEFT ignition |
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| |
module? |
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Yes |
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Is 24VAC |
| Probable cause is | |
present on VALVE | Yes | ||
failed wiring harness. | |||
terminal of ignition |
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module? |
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No |
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If fuse is not blown, module has failed.
