Rheem 96P series Installation Instructions Manual page 94

TABLE 20 (continued)
90P 2 STAGE FAULT CODES WITH DESCRIPTIONS AND SOLUTIONS
STATUS: This is a critical fault. The furnace will not operate in gas heat modes but all other modes (e.g. cooling) should
function if present simultaneously with a heating call (e.g. defrost call in dual-fuel mode).
DESCRIPTION: The low pressure control (or switch) should not be closed when the inducer is not running. If it is, this is a sign
of a serious condition. The switch may be welded closed or purposely bypassed in the field. Before any heat cycle can begin,
the pressure switch is tested to make sure that it is opened. The switch is ignored except in gas heating modes.
EXPECTED OPERATION: There will be no other operation than displaying of the fault code and diagnostic messages to the
homeowner and technician. The fault code is only present during a heat call before pre-purge begins. And will wait indefinitely
for the switch to open before clearing.
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CAUSE:
(1) Faulty switch.
(2) Pressure switch physically bypassed in the field.
(3) Loose or faulty wiring.
(4) Abnormally high negative pressure present on vent system without inducer running.
SOLUTION:
(1) Replace high pressure control (switch).
(2) Remove bypass and restore correct operation. Determine reason for bypass (e.g. vent length too long) and correct issue.
Notify homeowner and proper authorities of illegal tampering if necessary.
(3) Check wiring and connections. Replace and/or repair as necessary.
(4) Check for proper venting and terminations as defined in the furnace installation instructions.
STATUS: This is a critical fault. The furnace will not operate in gas heat modes but all other modes (e.g. cooling) should
function if present simultaneously with a heating call (e.g. defrost call in dual-fuel mode).
DESCRIPTION: This fault indicates that the low pressure switch is open when the inducer is energized at high speed. The
switch is ignored except in heating modes.
EXPECTED OPERATION: (1) DISPLAYED BEFORE HEAT IS ESTABLISHED: The IBM (Indoor Blower Motor) will not be
energized. The fault code will not be displayed until the IDM (Induced Draft Motor) has been energized for a minimum of ten
seconds. The IDM will remain energized at the high speed (high speed is default pre-purge speed) If the low switch is not
closed within 60 seconds the IFC will de-energize the IDM and enter a 5 minute soft lockout at which time it will begin pressure
switch proving attempts. If the pressure switch doesn't close within 60 seconds the cycle is repeated until either the pressure
switch closes or the heat call is lost. (2) DISPLAYED AFTER HEAT IS ESTABLISHED - If this fault is displayed after heat is
established, the gas valve will be de-energized, the IBM will be energized(if not already energized) at the correct heat speed
(determined by the firing rate required by the thermostat) and the IDM will remain energized at high speed. The IBM will
complete a 90 second blower off-delay and the IDM will complete a 20 second post-purge(at high speed). After these delays a
new attempt at ignition will be made provided the call for heat is still present.
CAUSE:
(1) Blockage or improper termination in either the inlet or exhaust vents.
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(2) The flue vent length and/or number of elbows exceeds the maximum number specified.
(3) Faulty or disconnected inducer.
(4) Faulty control board (inducer relay).
(5) Loose or faulty wiring
(6) Disconnected, blocked, split or cut pressure switch hoses.
(7) Wind gusts (sporadic).
(8) Faulty pressure switch.
SOLUTION:
(1) Check the vent system for blockage and proper termination and repair as necessary.
(2) Check the specification sheets and/or installation instructions. Remove excess venting.
(3) Repair or replace inducer and/or inducer wiring and/or electrical connections.
(4) Replace control board.
(5) Check wiring and connections. Replace and/or repair as necessary.
(6) Replace hoses as necessary.
(7) Insure proper termination and determine if high altitude kit may be necessary
(8) Replace the pressure switch.
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LOW PRESSURE SWITCH CLOSED, INDUCER OFF
LOW PRESSURE SWITCH OPEN, INDUCER ON HIGH SPEED