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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 15-pin connector
on the front of the
contactor box?
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.
24VAC Power Supply
Yes
System is OK.
Causes are broken or loose wiring
or a failed contactor. If wiring and
Yes
connections are verified to be intact,
replace contactor.
Is 24VAC
Yes
present on the load side of
the transformer?
No
Transformer has
failed. Replace.
7-15
In units with manual controls, verify the
continuity of the POWER switch in the ON
position. Replace switch as required.
Yes
If the switch is OK, causes are broken
or loose wiring. Check connections and
replace wiring as required.
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Table of Contents
Troubleshooting
