SERVICING & TROUBLESHOOTING HSI SYSTEMS SEQUENCE OF OPERATION

Upon a call for heat, the 50E47 or 50F47 ignition module is energized. If the module is a pre-purge model, pre-purge fan or relay will also be energized by the call for heat. When pre-purge time has elapsed, module will power the igniter within one second. Mod- ules without pre-purge will power igniter within one second of call for heat. When powered, igniter heats up to ignition temperature in either 17 or 45 seconds, depending upon module type. At the end of the igniter warm-up period, both valves in the 36E gas con- trol are opened. Igniter remains energized through a 7 second trial for ignition. If flame is detected by flame sensor within the igni- tion trial period, burner remains in operation until call for heat is satisfied. If flame is not detected, both valves are closed, igniter is de-energized and control module goes into lockout mode. Likewise, if flame is established and then lost, the control module will re-attempt the ignition sequence 4 times, and then lock out.

CHECKOUT PROCEDURE

1. Most 50E47 and 50F47 control modules are equipped with a diagnostic indicator light. Upon start-up the light will flash once, indicating the control is functioning. If system lockout occurs, diagnostic light will either flash on and off, or remain on. A steady “on” light indicates the fault is within the control module. Interrupt 25 volt power to the module momentarily, then reconnect. If light remains “on” constantly, module should be replaced.

2. If diagnostic light flashes after system lockout, it is an indica- tion that the problem is external from the control module --- either in one of the other components or in the system wiring. Disconnect system power at fuse or breaker. Check wiring for visual damage or loose grounds.

3. HSI systems are polarity sensitive and will lock out if polar- ity of 120 volt supply is reversed. To check polarity, disconnect the igniter socket from the wiring harness. Connect an AC volt- meter between the white igniter lead and ground; restore power to the system. There should not be voltage present between the igniter lead and ground. If voltage is present, polarity of supply power is reversed. Disconnect system power and switch 120 volt supply leads. Reconnect igniter to wiring harness, restore line voltage to system and check for proper operation.

4. If system does not operate, produce a call for heat and visu- ally check igniter for operation. Igniter should glow bright red within 7 seconds of call for heat or within 7 seconds after pre-purge period. If igniter does not heat up, check for 25 volts

across module terminals “TH” and “TR”. If 25 volts is pres- ent but system still does not operate, disconnect system power. Unplug igniter from wiring harness and check with ohmmeter for proper resistance -- 20 to 50 ohms. If resistance is not within 20 to 50 ohm range, replace igniter. If 25 volts was present be- tween “TH” and “TR” terminals, check for continuity between “IGN” and “L” terminals of module during call for heat (after pre-purge). If no continuity is detected, replace module.

5. If main burner does not ignite, check gas supply for proper pressure. Disconnect leads at gas valve and produce call for heat. Check for 25 volts across leads after igniter warm-up pe- riod. If 25 volts is measured, replace gas valve. If 25 volts is not present, check for 25 volts across “MV” and “MV” terminals of module. Replace leads if proper voltage is measured at module, replace module if 25 volts is not present.

6. If main burner ignites, but shuts off after ignition trial period, check flame sensor for carbon or dust buildup. With system power disconnected, check for resistance of at least 50 mego- hms between sensor lead (disconnected at module) and ground; replace sensor if 50 megohms is not present. If resistance is 50 megohms or more, check for continuity between sensor lead ter- minal and sensor probe. If no continuity exists, replace sensor. Check connection between module “GRD” terminal and burner for proper ground. Reconnect supply power and produce a call for heat. Check for proper position of sensor probe in flame; check sensor for output of 1.0 milliamp or greater. If adjustment of sensor position does not produce 1.0 milliamp output, replace sensor. If proper output current is measured but main burner will not stay on, replace control module.

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