Rheem 96P series Installation Instructions Manual page 96

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). If this fault is experienced during high
heat operation and the low pressure switch remains engaged, the furnace will switch to low fire heat and continue to run (if
possible) to try to satisfy the thermostat.
DESCRIPTION: This fault indicates that the high pressure switch is open when the inducer is energized at high speed. This
fault can be displayed any time during the heat call except during low heat call and only after the pre-purge and blower on delays
are complete.
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) for a period of five minutes
after the beginning of the pre-purge attempt. After five minutes, the IDM is de-energized and second attempt at pre-purge is
made (as long as the heat call is still present). This cycle is repeated indefinitely 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 IDM will
remain energized at high speed and the firing rate will drop to low stage provided the low pressure switch remains closed. The
IBM will energize at, or switch to, the low-fire rate (also provided the low pressure switch remains closed). Low heat is provided
until the heat call ends or the high pressure switch closes. If the high pressure switch closes, the heat rate and blower speed will
be adjusted to the correct (higher) rate required by the thermostat and the IDM will remain energized at high speed. If the low
pressure switch also will not remain closed, operation will be as described under fault code "46" (LPC OPEN) above. When the
high pressure switch is open and demand from the thermostat is set to 100% heat in this case the operation code "h" (for low
heat ) and the code "57" (open high pressure switch) will be displayed alternately.
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) High altitude kit not installed in areas of high elevation.
(6) Loose or faulty wiring.
(7) Disconnected, blocked, split or cut pressure switch hoses.
(8) Wind gusts (sporadic).
(9) 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 elevation of the installation and consult the specifications for the furnace to determine if a high altitude kit is needed.
Install proper kit as necessary.
(6) Check wiring and connections. Replace and/or repair as necessary.
(7) Replace hoses as necessary.
(8) Insure proper termination and determine if high altitude kit may be necessary.
(9) Replace the pressure switch.
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HIGH PRESSURE SWITCH OPEN, INDUCER ON HIGH SPEED