Operating and Safety Instructions
1. See Figure K10 for component locations.
2. This furnace module does not have a pilot. It is
equipped with a direct spark ignition device that au-
tomatically lights the gas burner. Do not try to light
burners by hand.
3. Before operating, leak test all gas piping up to heater
gas valve. Smell around the unit area for gas. Do not
attempt to place heater in operation until source of
gas leak is identified and corrected.
4. Use only hand force to push and turn the gas control
knob to the ‘On’ position. Never use tools. If knob
does not operate by hand, replace gas valve prior to
starting the unit. Forcing or attempting to repair the
gas valve may result in fire or explosion.
5. Do not attempt to operate unit if there is indication
that any part or control has been under water. Any
control or component that has been under water
must be replaced prior to trying to start the unit.
Start-up
1. Turn thermostat or temperature controller to its low-
est setting.
2. Turn off gas supply at the manual shut-off valve.
3. Turn off power to the appliance at the disconnect
switch.
4. Remove access panel or open door to appliance
vestibule housing the gas furnace.
5. Move gas control knob to ‘Off’ position. The furnace
module is provided with a supply air proving interlock
switch to ensure minimum supply airflow prior to
burner operation. Set the switch after ductwork has
been completed to open just below the minimum
supply airflow on the furnace rating plate.
6. Install a tapped fitting for attachment to a manometer
(or other gauge suitable for 14” w.c.) in the inlet pres-
sure tap and for 10” w.c. in the manifold pressure
tap.
7. Wait five minutes for any gas to clear out. If you smell
gas, see Step 2 above and correct leak. If you do not
smell gas or have corrected any leaks, go to the next
step.
8. Turn gas control knob to ‘On’ position.
9. Open all manual gas valves.
10. Turn power on at disconnect switch.
11. For start-up, temporarily set the DDC Control Sys-
tem for heating and to its highest position to initiate
call for heat and maintain operation of furnace. Con-
tinue start-up following the Sequence of Operation,
LED Flash Code Key and Troubleshooting Guide for
Fenwal 35-61 Series Direct Ignition Control based on
the burner firing rate control (on/off, two-stage or full
modulation) and Troubleshooting Guide provided on
the furnace at the end of this appendix.
12. Check and adjust manifold pressure (see Figure
a. The correct heat capacity of the furnace is con-
trolled by the burner orifices and the gas mani-
fold pressure. The manifold pressure is factory
set but should be checked at the time of start-up
as described below. For modulation control the
analog input signal could also be limited by the
control system depending on the airflow rate.
See
Airflow Considerations, Condensation and
Full Modulation Firing Rate Control
b. For two-stage and full modulation control sys-
tems manifold pressure should be 1.2” w.c. for
natural gas and 3.5” w.c. for propane during the
90 second warm-up period. Adjust low regula-
tor on two-stage gas valve, if necessary. After
90 seconds, manifold pressure should increase
to 3.5” w.c. for natural gas and 10.5” w.c. for
propane within 30 to 45 seconds for two-stage
units. For modulating units, after 90 seconds, the
manifold pressure will vary depending on the an-
alog input signal. At 10 VDC, pressure should be
3.5” w.c. for natural gas and 10.5” w.c. for pro-
pane; at 0V the manifold pressure should be 0.3”
w.c. for natural gas and 1.1” w.c. for propane.
c. For on/off units, the manifold pressure should
be 3.5” w.c. for natural gas and 10.5” w.c. for
propane.
Figure K11: Gas valve
WARNING – FOR YOUR SAFETY
The use and storage of gasoline or other flammable va-
pors and liquids in open containers in the vicinity of this
appliance is hazardous.
VCES-VHC-IOM-1F – VHC-36, -42 & -50
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