7.4.6 Technician Troubleshooting Guides
TROUBLESHOOTING THE 24VAC POWER SUPPLY SYSTEM
Verify that the power cord is properly connected to the electrical service and that the circuit breaker is not tripped.
On units with manual
controls, place the
POWER switch in the
ON position.
On units with computer
controls, place the
ON/OFF switch in the
ON position.
Was there an
audible snap from the contactor indicating the coil energized?
No
Is 24VAC present
across Pins 4, 5, and 6 of the
No
Is line voltage
present on the line side of the transformer?
No
Cause is loose or broken wiring, or the electrical service circuit is dead.
The primary indicator of a problem with the 24VAC Power Supply System is a failure of the power light to i l l u m i n a t e w h e n t h e POWER switch is placed in the ON position or the failure of the computer to a c t i v a t e w h e n t h e computer ON/OFF switch is pressed.
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| 24VAC Power Supply |
Yes |
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| System is OK. | |
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Causes are broken or loose wiring
Yes or a failed contactor. If wiring and connections are verified to be intact,
replace contactor.
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| In units with manual controls, verify the |
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| Is 24VAC |
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| continuity of the POWER switch in the ON |
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| position. Replace switch as required. | |
Yes |
| present on the load side of |
| Yes | |
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| If the switch is OK, causes are broken | |||
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| the transformer? |
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| or loose wiring. Check connections and | |
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| replace wiring as required. |
No
Transformer has failed. Replace.