Gas Heating Sequence Of Operations; Gas Heat Operation Errors - York International ZQ Series Installation Manual

correct setpoint will give shorter "ON" cycles and
may result in the lowering of the temperature within
the conditioned space.
Gas Heating Sequence of
Operations
When there is a W1 call for heat, the heat relay
(RW1) is energized by the unit control board (UCB).
The RW1-1 contacts immediately close energizing
the ignition control board (ICB). The ICB checks
the state of the flame sense circuit, the roll out
switch, the centrifugal switch and the primary /
auxiliary temperature limit switch circuit. If they
are in the expected state, then the ICB energizes
the draft motor and verifies that the centrifugal
switch located on the end of the draft motor closes.
After the centrifugal switch closes, a 15 second heat
exchanger purging period is completed. After this
purging period, the ICB will simultaneously energize
the pilot gas valve and the ignition coil. Once the
flame sensor senses a pilot flame is present, the
ignition coil is de-energized. The ICB checks for
pilot flame stability and once the ICB is satisfied
that the pilot flame is stable, the main gas valve
is energized by the ICB. The UCB will energize the
indoor blower after a 45 second delay from the call
for heat. The ICB and UCB both monitor the furnace
safety devices during the furnace operation. When
the call for heat is satisfied, the ICB closes the pilot
and main gas valves and performs a 30 second
purging of the heat exchanger by continuing the
operation of the draft motor. The UCB continues the
operation of the indoor blower for a configurable
amount of time after the call for heat is satisfied.
Two Stage Furnace Only
If a W1 only call for heat from a two stage
thermostat is present, then a two stage furnace
will start on high fire for 1 minute and then reduce
to low fire until the call for heat is satisfied or a
W2 call for heat is received. If a W2 call for heat is
received while in low fire operation, then the ICB
will immediately move to high fire operation. If a W1
and W2 call for heat is present, then the furnace will
remain on high fire operation until the W2 call for
heat is satisfied.
Automatic staging of a two stage furnace using
a single stage thermostat is possible. To achieve
automatic staging of a two stage furnace using a
single stage thermostat, cut the 440/GY wire that
runs from pin 2 of the S3 connector on the (UCB)
unit control board to P2-4 on the ignition control
board. Cut the wire 1/2 in. from the S3 mate-n-lock
66 INSTALLATION MANUAL ZQ SERIES 3 - 5 ton 60 Hertz R-410A
connector. Wire nut or tape off the 1/2 in. wire.
Attach the other end of the 440/GY wire to the R
terminal on the UCB, or to the TB1 power strip.
The unit will operate the same as a W1 only call
for heat for 10 minutes. If the call for heat is not
satisfied in the 10 minutes, then the ICB will move
to high fire operation until the W1 call for heat has
been satisfied.

Gas Heat Operation Errors

Temperature Limits
The primary limit is located such that the
temperature sensitive switch can sense the
temperature of the heat exchanger tubes. On single
or two stage models, the limit is mounted just above
the inlet of the heat exchanger tubes on the right
side. If a primary limit (LS) fault occurs (the primary
limit opens due to excessive heat exchanger
temperature), then the ICB will flash the appropriate
code (see Table 57) and monitor the primary limit.
The UCB will energize the indoor blower and the
ICB will energize the draft motor while the primary
limit is open. When the primary limit closes and the
call for heat still exists, the ICB will start the ignition
sequence over and the UCB will de-energize the
blower for 45 seconds. However, the auxiliary limit
is in series with the primary limit and it takes first
control. If the excessive heat has been high enough
to cause the auxiliary limit (AUX) to open, then the
ICB will flash the primary limit code but the furnace
will not retry ignition during the same call for heat.
The auxiliary limit is of the manual reset type and
is mounted in the upper right hand corner of the
panel between the burner manifold and the flue
gas collector box just behind the draft motor. If the
auxiliary switch has opened, then special attention
should be paid to the primary limit as it may be
faulty as well. However, the auxiliary switch is sized
such that multiple trips of the primary limit due to
complete blower failure will cause enough heat to
build up and trip the auxiliary.
If the primary limit opens three times within one
hour, the UCB will lock-out the indoor blower motor
and will initiate a flash code on the ETC, or send
an error message to the LCD Display on Smart
Equipment™.
Johnson Controls Ducted Systems