Rheem 97MDV060 Series Installation Instructions Manual page 63

START-UP AND SEQUENCE OF OPERATIONS
7. Low pressure switch fails to open after dropping
speed to the minimum RPM value during the calibra-
tion post-purge sequence.
8. The next heat cycle after the furnace has sensed and
shut down a heat cycle due to a Water Sensed condi-
tion.
9. A fault inhibiting gas heat call is detected in post-
purge during inducer ramp down operation during a
calibration sequence.
Note: If a calibration attempt fails, the furnace control will
enter five minute lockout and will NOT proceed into pre-
purge for a new heat cycle.
SHOULD OVERHEATING OCCUR OR THE GAS
SUPPLY FAIL TO SHUT OFF, CLOSE THE MANUAL
GAS VALVE FOR THE APPLIANCE BEFORE
SHUTTING OFF THE ELECTRICAL SUPPLY.
FAILURE TO DO SO CAN CAUSE AN EXPLOSION
OR FIRE RESULTING IN PROPERTY DAMAGE,
PERSONAL INJURY OR DEATH.
Calibration Cycle
The seven-segment display will display "CL" (for Calibra-
tion) at the start of cold calibration and through the warm
calibration sequence until the mid pressure switch is fully
calibrated (or fails to calibrate). After this, "H" or "h" will be
displayed as appropriate until the heat call has ended or a
fault has been declared. The text "CL" will then be dis-
played again during the warm low pressure switch calibra-
tion at the end of the heat call.
Cold Calibration
Upon entering calibration cycle, if all three pressure
switches are not open, the fault code "44" and/or "55"
and/or "65" (as appropriate) will be set and displayed im-
mediately on the dual Seven-Segment Displays (S.S.D.'s)
The IFC will wait indefinitely and will not proceed with the
heat call until both the high and low pressure switch cir-
cuits are determined to be open. This fault will continue to
flash both the high and low pressure switches finally open
even if the heat call is removed.
If the mid pressure switch is not open prior to calibration
operation, calibration will still proceed but without testing
the mid pressure switch and the proving and pre-purge se-
quences will continue as long as all other requirements
are met. Heating operation requirements between 50%
and 65% will fix the firing rate at 70% until a successful
calibration of the mid pressure switch is completed. Also, a
new calibration sequence will be executed on the next
heat cycle. The closed middle pressure switch fault will re-
main present until the switch is proven to be open – even
if the heat call is removed.
Calibration shall take place at intervals noted above when
a gas heat call is also present. When the inducer becomes
powered during calibration (high and low pressure
switches are open at the beginning), the IFC will finish the
cold calibration even if the gas heat call is removed during
the calibration process. If a fault inhibiting the gas heat call
becomes active during the calibration process, the calibra-
tion is interrupted immediately to allow proper response to
the fault. If a gas heat call is removed during a five minute
wait period after unsuccessful calibration, the calibration
cycle is interrupted immediately.
Low Pressure Switch Cold Calibration
Upon proving pressure switches open as noted above, the
furnace control will energize the inducer at a low starting
RPM. The furnace control will first verify that the inducer
drive is operating at the correct speed. After that,if the low
pressure switch does not close in within a few seconds,
the inducer speed will be increased slightly and the control
will again first verify that the inducer drive is operating at
the new speed and then wait for the low pressure switch
to close. This cycle repeats until the low pressure switch is
closed. If the RPM demand is at the maximum value for
the low pressure switch and the pressure switch still is not
closed, a fault code "46" will be set at level 1 and dis-
played at the seven-segment displays. The control will
shut off the inducer and enter a five minute wait period be-
fore attempting a new calibration sequence. The fault will
be elevated to level 2 after the second consecutive cali-
bration attempt has failed. The fault will remain at level 2
until the end of the lockout period even if the heat call is
removed. The "46" fault will be continuously displayed
until the heat call is removed or the pressure switch closes
in a subsequent attempt.
Immediately upon sensing the low pressure switch closed,
the RPM (demand) at which the inducer was running
when the switch closed will be added to a predetermined
value and the result will be stored in the furnace control
memory as the cold low pressure switch RPM.
If the mid pressure switch closes before the low pressure
switch, cold calibration of the low and mid pressure
switches is ended and operation will shut down while fur-
nace enters a five-minute wait period. The furnace control
will set and display fault code "46" at level 2 and a new
calibration attempt will be made after the five-minute wait
period. The fault will continue to be set and displayed until
the low pressure switch closes in the proper sequence
(before the mid pressure switch) during a calibration se-
quence.
Mid Pressure Switch Cold Calibration
Note: If the mid pressure switch is not open prior to cali-
bration, mid pressure switch calibration will not take place
and operation will proceed to the High pressure switch cal-
ibration.
Once the 40% heat inducer RPM is determined, the mid
pressure switch should be open. If the mid pressure
switch is closed, calibration will still proceed but without
verifying the mid pressure switch and the proving and pre-
purge sequences will continue as long as all other require-
ments are met. Heating demands between 50% and 65%
will fix the firing rate at 70% until a successful calibration
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