Honeywell S8910U User Manual

WARNING
FIRE OR EXPLOSION HAZARD. CAN CAUSE PROPERTY DAMAGE, SEVERE INJURY, OR DEATH.
Do not attempt to take apart the module or to clean it. Improper assembly and cleaning can cause unreliable
operation.
Regular preventive maintenance is important in applications that place a heavy load on system controls such as
those used in the commercial cooking and agricultural and industrial industries because:
In many such applications, particularly commercial cooking, the equipment operates 100,000 to 200,000 cycles
per year. This heavy cycling can wear out the gas control in one to two years.
Exposure to water, dirt, chemicals and heat can damage the gas control and shut down the control system. A
NEMA 4 enclosure can reduce exposure to environmental contaminants. See Electronic Ignition Service
manual, form 70-6604.
The maintenance program should include regular checkout of the system as outlined in the Startup and Checkout
section, and checkout of the control system as described in the appliance manufacturer literature.
Determine the maintenance frequency individually for each application:
Cycling frequency. Appliances that may cycle 20,000 times annually should be checked monthly.
Intermittent use. Appliances that are used seasonally should be checked before shutdown and again before the
next use.
Consequence of unexpected shutdown. Where the cost of an unexpected shutdown would be high, the system
should be checked more often.
Dusty, wet, or corrosive environment. Because these environments can cause the gas control to deteriorate
more rapidly, the system should be checked more often.
Replace any control if it does not perform properly on checkout or troubleshooting. In addition, replace any module if
it is wet or looks like it has ever been wet. Use protective enclosures, as described in Planning the Installation
section, regardless of checkout frequency.
OPERATION
The S8910U is a direct ignition control used with 120 Vac timed warmup hot surface igniter. The control provides
operating control and shuts off all gas flow on ignition failure or loss of main burner flame in central heat furnaces
and other heating appliances.
Module operation is in three phases—prepurge/igniter warmup, trial for ignition and burner operation. The S8910U
provides one or three trials for ignition, depending on which selection tab is installed. Fig. 8 shows the normal
operating sequence.
Purge/Prepurge
When the S8910U is used in a fan-assisted combustion system, the combustion air blower starts on a call for heat
from the thermostat. On proof of airflow, the air proving switch closes
and energizes the S8910U. When the S8910U is used in an atmospheric system, the call for heat energizes the
module. In either case, the S8910U first initiates a 32-second delay to allow system prepurge.
Igniter Warmup
After prepurge, the S8910U energizes the igniter to start the igniter warmup. The module energizes the hot surface
igniter for a 34-second warmup period; the gas control is closed during this period.
Trial for Ignition
At the end of the warmup period, the gas control opens for the ignition trial time determined by the selection tab. The
hot surface igniter stays powered for an ignition activation period of one second if the four-second trial time is used or
four seconds if the seven-second trial time is used. The igniter turns off after the ignition activation period. Near the
end of the ignition trial time, the flame rectification sensing circuit determines if the main burner flame is present. If so,
the gas control remains open and the burner operation phase begins.

Honeywell S8910U Specifications

General

Brand	Honeywell
Model	S8910U
Category	Control Unit
Language	English