IM 1093-1 • SINGLE DUCT VAV TERMINALS 8
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T
roubleshooTIng
Specific Electric Heat Troubleshooting Procedures:
WARNING
On all troubleshooting that requires you to work inside the
heater wiring casing, disconnect power first! Jumpers are
used for diagnostic purposes only – remove all jumpers prior
to returning unit to operation.
Possible Cause
Solution
Power not properly connected to the heater.
With a voltmeter, check the power wiring terminals to insure the proper voltage is available to the
element side of the power terminal block or to the field side of the disconnect switch, power fusing,
or circuit breakers. If proper voltage is not present, check the terminal studs for proper wiring and
check the power source for power.
Disconnect switch, toggle switch, or circuit breaker set to OFF
Set switch circuit breakers to the ON position.
Power fuses are blown or circuit breakers have tripped.
Replace fuses with the same type and amperage as those provided with the heater, or reset circuit
breaker by first setting the breaker to the OFF position, and then resetting it to the ON position.
With an ammeter, check amperage draw on the power lines. For heaters with fusing, amperage
draw should not exceed the fuse. For heaters with circuit breakers, amperage should not exceed
the rated value. If the amperage draw is excessive, check the power supply as described above
for proper voltage. If the fuse/circuit breaker trips upon application of power, check for a short. If
no short is present and the power supply wiring/voltage is correct, contact the factory for further
assistance.
Manual reset switch has been tripped.
Push manual reset button. Manual reset is usually located in the control cabinet near the bottom of
the been tripped. element header.
Air static switch is not engaging.
Jumper out the air static switch by connecting the lead attached to the normally open stud, to the
normally closed stud. If heater operates, the problem may be the air static switch. Disconnect the
pneumatic tubing from the pitot tube located in the control cabinet. Attach a magnehelic gauge to
the pitot tube. Available static pressure at the pitot tube should be <= -0.03" S.P. or >= +0.03" S.P.
If the available static pressure is in the dead band between these two ranges, the switch will not
engage and some method must be devised to increase the available static pressure. If sufficient
static pressure is available, check to insure the pneumatic tube is connected to the correct port of
the switch. For negative pressure, connect to the low port. For positive pressure, connect to the
high port. If the air static switch still fails to operate, contact the factory for a replacement switch.
Automatic reset switch bad.
Allow the duct temperature to cool below 90°F. If the heater does not operate, jumper out the
automatic reset switch. If the heater now operates, contact the factory for a replacement switch.
Manual reset switch Allow the duct temperature to cool below 90°F. If the heater does not operate,
do the following:
• On heaters with the manual reset installed in the power wiring, jumper out the manual reset
switch. If the heater now operates, contact the factory for a replacement switch.
• On heaters with the manual reset located in the backup contactor circuit, jumper out the manual
reset switch. If the backup contactor now engages, contact the factory for a replacement switch.
If the backup contactor fails to operate, the problem is in the backup contactor holding coils. Use
an ohmmeter to check the continuity of the holding coils. Contact the factory for a replacement of
any contactor with faulty holding coils.
Step controller malfunction.
Jumper out each step of the step controller. If contactor engages, the trouble is in the step
controller. Refer to the literature provided with the step controller for proper power and wiring. If
wiring appears to be correct, contact the factory for assistance.
SCR controller malfunction.
Refer to the literature provided with the SCR controller for proper power and wiring. If wiring
appears to be correct, contact the factory for assistance. Possible: Nuisance Tripping of Reset
Switchs
Insufficient air flow across the heating elements
The minimum allowable air flow across the heating coils is 70 CFM/kW. Unless this minimum air
flow is met, the leaving air temperature will be greater than the set point of the high temperature
limit switches. This will cause nuisance tripping of the reset switches. Reset the minimum air flow
across the coils to the minimum listed value. If further assistance is needed, contact the factory
