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3.2.3. Combustion Air Inducer (CAI) Proof Switches (S18 and S45)
3.2.3.1. Open Proof Sequence of Operations
A The M3 Unit Controller will set alarm 166 and/or 167 if either S18 or S45 are not proved open while the combustion air
blower is not energized. If gas heat demand is still present, the M3 Unit Controller will attempt to prove either S18 or S45
are in a open condition every 60 seconds.
B If either S18 or S45 are proven as open, the M3 Unit Controller will proceed with the gas heat demand (i.e energize the
the combustion air blower).
C Even while lockout alarm(s) 168 and or 169 are active, the M3 Unit Controller will continue attempting if either S18 or
S45 are open. Parameter 72 - Max CAI No Open Proof Occurrences default setting is 5 and it adjustable from 1 to 15
occurrences.
D The M3 Unit Controller will set alarm(s) 168 and/or 169 (instead of 166/167) if either S18 or S45 are not proved open
while the combustion air blower is not energized, for 5 consecutive times during a single cycle. Even while alarm(s) 168
and/or 169 are active, the M3 Unit Controller will continue attempting to prove that either S18 and/or S45 are open.
Parameter 72 Max CAI No Open Proof Occurrences default setting is 5 and it adjustable from 1 to 15 occurrences.
To view or change the number of occurrences setting, go to SETTINGS > RTU OPTION > EDIT PARAMETER = 72
(MAX CAI NO PRF OCC)
ALARM
CODES
TYPE
TABLE 8. OPEN PROOF ALARMS
DISPLAY MESSAGE Event Action
166 ALARM
CAI PRESSURE SWITCH STUCK CLOSED
GV1
This alarm will occur when the combustion air pressure switch (S18) is
detected as closed immediately after the furnace demand relay is ener
gized and before the combustion air blower is energized. Gas valve 1.
167 ALARM
CAI PRESSURE SWITCH STUCK CLOSED
GV2
This alarm will occur when the combustion air pressure switch (S45) is
detected as closed immediately after the furnace demand relay is ener
gized and before the combustion air blower is energized. Gas valve 2.
168 ALARM
COMBUSTION AIR SW NOT OPEN LOCKOUT
GV1
System locked out due to S45 switch closed and a specific number
occurrences detected based on Parameter 72 (MAX CAI NO PRF OCC)
setting during a single cycle.
169 ALARM
COMBUSTION AIR SW NOT OPEN LOCKOUT
GV2
3.2.3.2. Closed Proof Sequence of Operations
A The M3 Unit Controller will set an alarm(s) (Alarm 56 or 66) if:
If either S18 or S45 switches are not sensed as closed within 30 seconds of energizing the Combustion Air Blower.
If either S18 or S45 switches are sensed as open for three seconds while gas heat demand is active.
B The M3 Unit Controller will set an alarm(s) 57 and/or 67 when three-strikes occur during a single-demand. Parameter 71
default setting is 3 and it adjustable from 1 to 5 occurrences.
To view or change the number of occurrences setting, go to SETTINGS > RTU OPTION > EDIT PARAMETER = 71
(MAX CAI NO SW OCC)
ALARM
CODES
TYPE
TABLE 9. CLOSED PROOF ALARMS
DISPLAY MESSAGE Event Action
56 ALARM HEAT 1 CAI SWITCH S18 Check heat section 1 combustion air motor and proof switch.
57 ALARM STRIKE 3 HEAT 1 CAI SWITCH S18
Check heat section 1 combustion air motor and proof switch. Number of
occurrences is reached.
66 ALARM HEAT 2 CAI SWITCH S45 Check heat section 2 combustion air motor and proof switch.
67 ALARM STRIKE 3 HEAT 2 CAI SWITCH S45
Check heat section 2 combustion air motor and proof switch. Number of
occurrences is reached.
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