Reznor PDH Operation Manual PreevA - Manual (Page 12)

Form O-PreevA, Page 12
3.4 Gas-Fired Heat
Section -
PDH, SDH, RDH,
RHH, & SHH
3.4.1 Heat Exchanger Maintenance
The gas furnace section includes a patented
T
CORE
2
® burner and primary heat
exchanger. High efficiency Models RHH & SHH also have a secondary heat exchanger.
Remove any external dirt or dust accumulation. Visually check the heat exchanger for
cracks and holes. If a crack or hole is observed, replace the heat exchanger.
NOTE: Inspection of the lower portion of the heat exchanger is done with the burner
removed. See the Burner Maintenance section below for information on inspecting the
lower portion of the heat exchanger.
This heater is equipped with a
T
CORE2 ® burner.
Inspect the burner/control compartment annually to determine if cleaning is necessary.
If there is an accumulation of dirt, dust, and/or lint, clean the compartment and follow
the instructions below to remove and the burner for inspection and/or cleaning.
CAUTION: Use of eye protection is recommended.
1. Outside the cabinet, shut the gas supply off at the manual valve ahead of the
union.
2. Turn off electric supply.
3. Open the burner cabinet door.
4. Loosen the screw holding the burner shield end and remove the burner shield end.
(See FIGURE 2.)
5. At the union closest to the burner, disconnect the gas supply. Do not allow the
portion of the gas train attached to the venturi tube to rotate.
6. Remove Burner Assembly - The burner assembly is designed to slide out of the
heater for inspection and/or service. Carefully pull the burner assembly end (with
pipe nipple attached) out of the heater. To completely remove the burner assembly,
disconnect the sensor and ignitor wires. Slide the burner out of the cabinet.
With the burner assembly accessible, shine a flashlight on the burner ribbons. Look
for carbon buildup, scale, dust, lint, and/or anything that might restrict flow through the
spaces between the burner ribbons.
If it is determined that the burner needs to be cleaned, hold the burner assembly so
that any foreign material will fall away from the burner, use a stiff bristle brush to loosen
and remove any foreign material(s). If the burner is excessively dirty, remove one of the
burner end caps. Remove the four screws that hold the end cap to the burner housing.
Lightly tap the end cap to remove it.
Burner Removal
Instructions
3.4.2 Burner
Maintenance
Inspect and Clean the
Burner
3.3.7 Ignition Control
Module - Gas Heat
Section with Control
Option AG58 or D12G
(cont’d)
3.0 Maintenance
Procedures
(cont’d)
3.3 Electrical
Compartment
(cont’d)
time while in prepurge, the prepurge time is restarted. If flame is present long enough
to cause lockout, refer to the Troubleshooting Guide in Paragraph 4.2. The ignition sys-
tem circuit board runs the venter motor for a 30-second prepurge time, then proceeds
to the ignition trial period.
3) Ignition Trial Period - The ignition system circuit board energizes the spark and
main gas valve. The venter remains energized. If flame is sensed during the first 6
seconds, the spark is de-energized. If flame has not been sensed during the first 6 sec-
onds, the control de-energizes the spark output and keeps the gas valve energized for
an additional one second flame proving period. If flame is not present after the flame
proving period, the control de-energizes the gas valve and proceeds with three ignition
re-tries as specified in “Abnormal Heat Cycle, Ignition Retry”. If flame is present, the
circuit board proceeds to steady heat. After three re-tries, the board will lockout for one
hour. It will require a cycling of power to reset before the one-hour limit.
4) Modulating Heat - As long as the call for heat exists, the circuit board not only
modulates the gas to precisely meet varying load conditions, but also modulates the
combustion air to maintain stable performance and optimize thermal efficiency across
the entire modulating range. Circuit board inputs are continuously monitored to ensure
limit switch is closed and flame is established. When the call for heat is removed, the
ignition system circuit board de-energizes the gas valve and begins postpurge timing.
5) Post Purge - The venter motor output remains on for a 45 second postpurge period
after the system controller is satisfied.
Modulating Gas Control Sequence of Operation - applies to Gas
Control Option AG58 or D12G (cont’d)