Gas Heating Sequence Of Operations; Gas Heat Operation Errors; Gas Valve Piping - Johnson Controls TempMaster ZD Series Installation Manual

5742640-TIM-A-0419
Table 22: Electric Heat Anticipator Setpoints
Heater
Voltage
Kw
10
15
575-3-60
20
30

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.
Redundant valve
Gas main
Gas Valve
Figure 22: Gas Valve Piping
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" from the S3 mate-n-lock connector. Wire nut or tape off the
52
Setting, Amps
TH1 TH2
0.35 -
0.35 -
0.37 0.29
0.37 0.29
Main valve
To main burner
To pilot burner
1/2" 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

During furnace operation, the ICB monitors the flame sense
circuit, the centrifugal switch, the primary limit switch and the
roll out switch. If a signal from any of the inputs moves to a fault
state, then the ICB immediately closes the pilot and main gas
valves. The ICB will determine the device that is signaling a
fault and flash a code for that device. A primary limit trip,
centrifugal switch trip or flame sense fault triggers a temporary
lock out. An auxiliary limit or a roll out switch trip requires
intervention to reset the ICB. The UCB also monitors the
primary limit and gas valve.
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 (Table 29) 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, then the
UCB will lock on the indoor blower and send an error code on
the LCD Smart Equipment™ Control.
Gas Valve
The UCB monitors the gas valve (GV). Any time the UCB senses
voltage at the GV without a call for heat for a continuous five-
minute period, the UCB will lock on the indoor blower and send a
error message to the LCD Smart Equipment™ Control. When
the UCB no longer senses voltage at the GV the UCB will de-
energize the indoor blower after the expiration of the indoor
blower heating off delay.
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