System Fault Low Air Pressure Or Purge - Aerco Benchmark Series User Manual

11. Reconnect the 1 ¾" connector to the control
panel.
12. Reconnect AC power to the unit and start
the unit.
13. If the blower proof fault still persists, replace
the combustion safeguard.
8.6.5 MOTOR CONTACTOR
1. Open the controls box and locate the motor
contactor.
2. Locate wire #36. Measure the AC voltage on
its terminal when the unit is attempting to
start. There should be 120VAC at this point.
3. If 120VAC is measured on this terminal and
the blower still does not start, replace the
motor contactor.
4. If 120VAC is not measured, remove the
cover from the combustion safeguard
connect a voltmeter to terminal # 8 and the
unit frame.
5. Start the unit. The voltmeter should measure
120VAC. If 120VAC is not measured
replace the combustion safeguard chassis.
8.7 SYSTEM FAULT LOW AIR PRESSURE OR
PURGE INTERLOCKS
A system fault indicates when the unit faults
during the starting sequence, but prior to
ignition. An internal 30-second fault timer starts
timing when the unit start sequence is initiated. If
ignition is not reached within the specified time,
the Annunciator displays the message SYSTEM
FAULT LOW AIR PRESSURE or PURGE
INTERLOCKS depending on the cause. A
system fault usually occurs when the system
does not acknowledge either the safety shut-off
valve proof of closure switch, the blower proof
switch, or the air/fuel valve open switch.
8.6.1 Determining the
8.6.2 Blower
8.6.3 Combustion Air Supply and Blower
Proof Switch
8.6.4 Purge Interlocks
8.6.5 SSOV Proof of Closure Switch
8.6.6 Air/fuel Valve Open Proving Switch
8.6.7 Air/Fuel Valve not Rotating
8.6.8 Air/Fuel Valve Ignition Position Switch
Recommended Troubleshooting
DVM
8.7.1 DETERMINING THE CAUSE
1. Clear the Annunciator and start the unit.
,
C
ause
Equipment
TROUBLESHOOTING
2. If the blower does starts and the message
SYSTEM FAULT PURGE INTERLOCKS is
displayed proceed to section 8.6.4
3. If the blower does not start, and the
message SYSTEM FAULT LOW AIR
PRESSURE is displayed, proceed to section
8.6.2.
4. If the blower starts and the message
SYSTEM FAULT LOW AIR PRESSURE is
displayed, proceed to section 8.6.3.
5. If the unit does not fire, and the message
SYS FLT is displayed on the temperature
controller and the Annunciator, proceed to
section 8.6.8.
8.7.2. BLOWER
1. Locate wire #81 & #83 on the motor
contactor located inside the control panel.
2. Connect an AC voltmeter between wire #81
and wire #83 and the unit frame.
3. Start the unit.
4. The AC voltmeter should measure between
200 and 230VAC.
5. If 200 to 230VAC is not measured, proceed
to section 8.5.5
6. If 200 to 230VAC is measured, check for
voltage between wire #131 and #132 at the
blower motor.
7. If 200 to 230 VAC is present between wire
#131 and #132 and the blower still does not
start replace the blower assembly.
8.7.3 COMBUSTION AIR SUPPLY AND
BLOWER PROOF SWITCH
1. If the unit has sealed combustion, check the
ducting for any signs of blockage.
2. If combustion air is brought in through an
opening in a wall, be sure that the size of the
opening is adequate and that louvers are
open while the unit is firing.
3. If the combustion air supply is okay, remove
wires #154 and #155 from the blower proof
switch.
4. Connect an ohmmeter across the blower
proof switch and start the unit.
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