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NO
YES
UNIT RUNS BUT SHUTS OFF BEFORE THERMOSTAT IS SATISFIED−INSUFFICIENT HEAT
CHECK FOR RECIRCULATION OF EXHAUST GASES TO AIR
INTAKE AT THE OUTSIDE TERMINATIONS OF PVC PIPING.
MODIFY OR CORRECT
SEPARATION TO A
MAXIMUM OF 3".
ARE INTAKE AND EXHAUST PVC LINES TERMINATED
INTO A WINDOW WELL, ALCOVE OR CORNER WHERE
VARYING CONDITIONS CAUSE RECIRCULATION?
IF OUTSIDE TEMPERATURE IS LOW ENOUGH,
OBSERVE EXHAUST OUTLET VAPOR WHEN
UNIT IS RUNNING. RECIRCULATION WILL
EASILY BE SEEN.
MODIFY OR CORRECT
TERMINATIONS TO
ELIMINATE RECIRCULATION.
NO
YES
ARE INTAKE AND EXHAUST PVC LINES SEPARATED AT
OUTSIDE TERMINATION? DOES EXHAUST TERMINATION EXTEND
AT LEAST 8" PAST INTAKE TERMINATION?
MODIFY OR CORRECT
TERMINATIONS TO
ELIMINATE RECIRCULATION.
NOTE: RECIRCULATION IS ALSO POSSIBLE
WHEN EXHAUST C02 CONTENT IS ABOVE
10%. THIS IS DIFFICULT TO MEASURE AS
AN INDICATION IN THIS CASE IF UNIT WILL
ONLY RUN FOR 10 SECONDS OR LESS.
RECIRCULATION
CHECKS
ARE LIMITS CUTTING OUT UNIT? CHECK FOR OPEN LIMIT
IMMEDIATELY FOLLOWING UNIT CUTOUT. SHUT OFF POWER
AND MAKE OHM METER CHECK.
NO
IS GAS PRESSURE LOW?
CHECK FOR INTERMITTENT LOW GAS PRESSURE.
(MONITOR LOW GAS PRESSURE)
NO
YES
CORRECT GAS PRESSURE.
IS EXHAUST, INTAKE OR CONDENSATE PVC PIP
ING
PARTIALLY BLOCKED OR RESTRICTED?
NO
YES
ELIMINATE BLOCKAGE AND RETEST.
YES
IS FILTER CLEAN AND PROPERLY INSTALLED?
ARE SUPPLY AND RETURN AIR DUCTS UNRESTRICTED?
CORRECT IF NECESSARY AND RETEST.
MAKE OHM METER CHECK ACROSS
TERMINALS IMMEDIATELY AFTER
UNIT SHUTS OFF. METER READS
OHMS WHEN SWITCH
CUTS UNIT OUT.
CHECK GAS BTUH INPUT.
IS INPUT HIGH? OUT OF ACCEPTABLE RANGE?
NO
YES
IS MANIFOLD PRESSURE TOO HIGH?
IS TEMPERATURE RISE AND
STATIC PRESSURE
WITHIN PROPER RANGE.
NO
YES
ADJUST GAS VALVE
REGULATOR.
NO
YES
REPLACE LIMIT.
ADJUST
BLOWER
SPEED.
5
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