York ZF076 Installation Manual page 48

5725848-XIM-A-0319
per the wiring diagram. Place the gas valve in the on
position and verify proper furnace operation.
2. If the flash code indicates the switch is closed with the draft
(inducer) motor off (flash code 3), then disconnect the 9 pin
connector from the ICB and measure the continuity of the
centrifugal switch with a battery powered test light or an
ohm meter between terminals 3 and 8 of the harness
connector. If a closed circuit is indicated, then check the
wiring between the ICB and the draft motor. If the wiring is
not shorted together, then replace the draft motor. If an
open circuit is indicated, then reconnect the 9 pin wiring
harness to the ICB and remove power to the unit for at
least 20 seconds. Restore power to the unit. If the ICB
continues to flash a code 3, then replace the ICB.
Pilot flame lockout
The ICB counts the number of flame losses during the same
call for heat. If more than 16 flame losses occur within the same
call for heat, then the control temporarily locks out furnace
operation for 5 minutes (flash code 5). If the call for heat
remains after the 5 minutes, then the ICB will retry the ignition
sequence. The flame losses can be due to low inlet pressure,
debris around flame sensor, plugged pilot burner, soot on the
surface of the flame sensor or misadjusted pilot pressure.
Remove the power to the unit for 20 seconds and then restore
power to the unit. Induce a call for heat and observe the pilot
flame in the flame sensor area to determine the best course of
action.
1. If the flame is strong and stable in the flame sensor area,
then verify the position of the flame sensor per the start up
procedures. If ok, then remove the flame sensor and check
the cleanliness of the electrode. If clean, then replace the
flame sensor and adjust pilot per the start up procedures. If
not clean, then clean, reinstall and adjust pilot per the start
up procedures.
2. If the flame is weak or unstable in the flame sensor area,
then verify the gas inlet pressure. If gas inlet pressure is
above the minimum inlet pressure stated on unit data label,
then adjust the pilot pressure per the start up procedures. If
the pilot cannot be adjusted to obtain a strong and stable
flame in the flame sensor area, then remove the burner
assembly and verify the pilot burner assembly is open
internally and the holes in the burner are clean. Check the
pilot orifice size to the unit data plate and the cleanliness of
the pilot orifice. Verify that the flame sensor electrode is
clean and is adjusted properly. After cleaning or
replacement of the pilot assembly components, reinstall
the burner assembly and adjust pilot per the start up
procedure.
Primary or aux temperature limit
The temperature limits limit the temperature in the furnace to a
safe level. If a temperature higher than the preset limit is
achieved due to low or no air flow through the furnace, then the
temperature limits opens and the ICB closes the gas valve and
flashes code 6. The primary limit is automatic reset type while
the auxiliary limit is manual reset type. If either one opens, then
the ICB removes power to the gas valve and the UCB
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energizes the indoor blower until the primary limit automatically
resets or the auxiliary limit is manually reset. Verify adequate air
flow through the furnace. If air flow is nonexistent or weak, then
troubleshoot and repair the conditioned space air circulation
system as necessary. Reset the auxiliary limit and verify proper
operation of the furnace. If airflow is normal, then verify the gas
input rate to the furnace following the start up procedures
(auxiliary limit must be reset before the furnace will operate). If
after verifying the circulating air system, the input rate to the
furnace and that the air temperature rise through the furnace is
within the rise range on the unit data plate the flash code still
exists, then set the gas valve to the off position and temporarily
apply control voltage (~24 volts) to pin 9 of the 9 pin ICB
connector. With power applied to the unit, if the ICB LED
continues to flash a code 6, then replace the ICB and return unit
to operation (you must remove the temporary voltage to pin 9
before the gas valve is turned on). If the ICB LED flashes a
heartbeat, then replace the limit that is opening, remove the
temporary voltage applied to pin 9, turn on the gas valve, restart
the furnace and verify proper operation of the furnace.
Rollout switch
The rollout switch is installed to protect the furnace from
damage due to excessive heat in the burner area. There are 4
main reasons the rollout switch will open (flash code 7) due to
excessive heat in the burner area. You must remove power to
the unit for 20 seconds to reset the ICB.
1. A blocked flue outlet is the most common cause for the
rollout switch to open. Check the flue outlet for debris and
clear if necessary.
2. Loose blower wheel on draft motor. Verify that the blower
wheel is securely fastened to the draft motor shaft.
3. Unit operating outside the air temperature rise range stated
on the unit data plate. Either the air flow through the
furnace is not sufficient or the gas input rate to the furnace
exceeds the recommended rate. Verify both conditions are
within the published ranges.
4. Cracked heat exchanger tube(s). If a heat exchanger tube
or tubes is cracked, then the flow through the heat
exchanger is restricted and the flame will either roll out of
the tube inlet or heat will build to an abnormal level in the
burner area. This can usually be determined by observing
burner flame with and without indoor blower operation. If
the flame changes when the blower is running compared to
when it is not, then visually inspect the heat exchanger
tubes.
If all of the above are found to be in good condition or within the
operating ranges, then set the gas valve to the off position and
temporarily apply control voltage (~24 volts) to pin 6 of the 9 pin
ICB connector. With power applied to the unit, if the ICB LED
continues to flash a code 7, then replace the ICB and return unit
to operation (you must remove the temporary voltage to pin 6
before the gas valve is turned on). If the ICB LED flashes a
heartbeat, then replace the rollout switch, remove the
temporary voltage applied to pin 6, turn on the gas valve, restart
the furnace and verify proper operation of the furnace.
Johnson Controls Ducted Systems