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20
Vl & Vm Sheaves Adjustment
1. Loosen set screw “B” using a 5/32” Allen key.
2. Making half or full turns from closed position, adjust
sheave pitch diameter for desired speed. DO NOT
OPEN MORE THAN SIX FULL TURNS.
3.
Tighten set screw “B” securely over flat.
4. Carefully put on belts and adjust belt tension. DO
NOT FORCE BELTS OVER GROOVES.
5. Ensure all keys are in place and the set screws tight
before starting drive. Recheck set screws and belt
tension after 24 hours service.
NOTE: Future adjustments should be made by
loosening the belt tension and increasing or
decreasing the pitch diameter of the sheave by
half or full turns as required. Readjust belt
tension before starting drive.
C
B
VL & VM
NOTE: Do not operate sheave with flange
projecting beyond the hub end.
Electrical Input Check
Make preliminary check of evaporator fan ampere draw
and verify that motor nameplate amps are not exceeded. A
final check of amp draw should be made upon completion
of air balancing of the duct system (see Appendix B).
GAS SYSTEM CHECK
Pre-Operation Checks
1. Close the manual gas valve external to the unit.
2.
Turn off the electrical power supply to the unit.
3. Change heating setpoint to its lowest possible setting.
4. Remove the heat exchanger door on the side of the
unit by removing screws.
5. This unit is equipped with an ignition device which
automatically lights the main burner. DO NOT try to
light burner by any other method.
6. Move the gas control valve switch to the OFF position.
7.
Wait five minutes to clear out any gas.
8. Smell for gas, including near the ground. This is
important because some types of gas are heavier
than air. If you have waited five minutes and you do
smell gas, immediately follow the warning WHAT TO
DO IF YOU SMELL GAS on page 2 of this manual.
If having waited for five minutes and no gas smell is
noted, move the gas control valve switch to the ON
position.
9. Replace the heat exchanger door on the side of the
unit.
10. Open the manual gas valve external to the unit.
11. Turn on the electrical power supply to the unit.
12. Change heating setpoint to desired setting.
Gas Supply Pressures & Regulator Adjustments
WARNING
Should overheating occur or the gas supply fail
to shut off, turn off the manual gas shutoff
valve external to the unit before turning off the
electrical supply.
WARNING
To avoid property damage, personal injury or
death, do not fire gas unit with flue box cover
removed.
NOTE: Except during brief periods when gas
pressures are being measured by qualified
service personnel, the furnace access panel must
always be secured in place when the furnace is in
operation. An inspection port in the access panel is
provided to monitor the flame.
The first step in checking out the gas-fired furnace is to test
the gas supply piping to the unit for tightness and purge the
system of air using methods outlined in the latest edition of
the National Fuel Gas Code ANSI Z223.1 / NFPA 54. Verify
that the disconnect switch is in the “OFF" position. A soapy
water solution should be used to check for gas leaks.
Since the unit is subject to considerable jarring during
shipment, it is extremely important that all gas connections
and joints be tested for tightness. Gas piping downstream
from the unit inlet should be checked for leaks during the
subsequent sequence check.
The supply gas pressure should be adjusted to 7.0” w.c.
on natural gas and 11.0” on LP gas with the gas burners
operating. If there is more than one unit on a common gas
line, the pressures should be checked with all units under
full fire. A supply pressure tap is provided on the upstream
side of the gas valve. A manifold pressure tap is provided
on the manifold. The normal manifold pressure for full input
is 3.5” w.c. on natural gas and 10.0” w.c. for propane gas.
Minimum gas supply pressure is 5.5” w.c. for natural gas
and 11.0” for propane gas. In order to obtain rating, gas
supply pressure must be 11.0” w.c. for propane gas.
Summary of Contents for DBG Series
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