Rheem 96P series Installation Instructions Manual page 95

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: This fault indicates that the low pressure switch is open when the inducer is energized at low speed. Since the
furnace only ignites at high fire, this condition should never be seen except after the blower on delay period of the ignition cycle
and only after the furnace attempt to switch to low stage heating. The switch is ignored except in heating modes.
EXPECTED OPERATION: This fault is displayed only after heat is established and switched to low fire with the IBM (Indoor
Blower Motor) energized at low speed. When this fault is displayed the gas valve will be de-energized, the IBM will remain
energized at the low heat speed and the IDM (Induced Draft Motor) will remain energized at the low speed. The IBM will
complete the user-selected blower off-delay (at low speed) and the IDM will complete a 20 second post-purge (at low 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.
(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.
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(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.
(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.C350:K376C408C358:K376
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 high 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.
CAUSE:
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(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.
LOW PRESSURE SWITCH OPEN, INDUCER ON LOW SPEED
HIGH PRESSURE SWITCH CLOSED, INDUCER OFF
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