York ZS Series Installation Manual page 69

3. With the draft motor running, check for 24 volts at the
pressure switch terminal on the ICB. If not present, check
for 24 volts on the terminal from the pressure switch. If
present, go to step 4. If 24 volts is not present, the either
pressure or rollout switch is not closed. Or the draft motor
is not sufficiently evacuating the heat exchanger tubes or
the pressure switch has failed. Check the operation of the
pressure switch. Check the line voltage to the unit; if line
voltage is low, call the local power company. If the problem
persists, the draft motor may need replacement.
4. If the furnace is hot, it may be out on a high temperature
limit open; wait for limit reset.
5. If all are intact replace the ICB.
The draft motor runs and the spark ignitor sparks at the burner,
but the burner does not ignite and a gas odor is not detected at
the draft motor outlet.
Subject to change without notice. Printed in U.S.A.
Copyright © 2010 by Johnson Controls, Inc. All rights reserved.
1. Check to ensure gas is being supplied to the unit. Confirm
that the gas pressure to the unit is within the proper limits
as described in the "POST START CHECKLIST".
2. Check the voltage at the gas valve and at the gas valve
terminals on the ICB. Check all wiring between the ICB and
the gas valve. Check to make sure the ground connections
are intact.
3. If 24 volts is present, remove the pilot burner and the
orifice. The removal procedure is described in "BURNER/
ORIFICE INSPECTION/SERVICING." Inspect the orifice
for obstruction. If it is clear, replace the gas valve.
Main burners light but exhibit erratic flame characteristics.
1. Check the main burner orifices for obstruction and
alignment. The removal procedure is described in
"BURNER/ORIFICE INSPECTION/SERVICING". Clean or
replace burner orifices and burners as needed.
Johnson Controls Unitary Products
5005 York Drive
Norman, OK 73069
518676-BIM-C-0610
Supersedes: 518676-BIM-B-1109