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service instructions <br /> BLOCKED VENT <br /> SAFETY SWITCH <br /> t <br /> ALUMINIZED - <br /> STEEL DRAFT <br /> DIVERTER "' ADJUSTABLE <br /> AIR DEFLECTOR <br /> BLADES <br /> VENT PIPE <br /> CONNECTION <br /> ALUMINIZED <br /> STEEL HEAT <br /> EXCHANGER <br /> FAN & <br /> FAN GUARD <br /> i <br /> LIMIT CONTROL i "j 3` <br /> MAIN -. <br /> BURNER <br /> COMBUSTION <br /> AIR INLETS <br /> Figure 13 <br /> Cross-section of propeller type unit <br /> LIMIT CONTROL(OVERHEAT SWITCH) IMPORTANT NOTE: <br /> The limit control, mounted on the left inner side panel (when The limit control(overheat switch)on this unit heater will <br /> facing front of unit), will shut off the gas supply to the main shut off the gas should excessive discharge temperatures <br /> burner in the event of overheating. It is a single pole single- occur.Do not attempt to control the fan with the limit control. <br /> throw switch.This limit control should operate only when something Any change in wiring to attempt to control the fan with <br /> is seriously wrong with the unit.Anytime this control operates, the limit control will result in hazardous conditions and <br /> correct the difficulty immediately or serious damage may result. void the warranty. <br /> If the limit control cuts off the gas supply during normal operation: <br /> BLOCKED VENT SAFETY SWITCH <br /> 1.See that front louvers are open and that there are not any A blocked vent safety switch is supplied on all gravity-vented <br /> obstructions in the air inlet or discharge outlet. unit heaters and is designed to prevent operation of the main <br /> 2.Check actual input to unit against rated input. gas burner if the venting system is blocked. <br /> 3.Check to be sure motor is operating If the blocked vent switch has tripped, turn off the gas and <br /> 4.Check that fan is not loose on motor shaft.On blower units electric supply to the unit heater.Check the entire vent system <br /> check belts and pulleys for tightness or damage. connected to the unit heater for blockage or damage. <br /> 5.Check fan speed(on propeller units)against speed on mo- After the vent system has been cleared, or if no blockage or <br /> for nameplate.On blower units check blower speed against damage is found in the vent system,the blocked vent switch <br /> Tables 9 or 10; check for restrictions in ducts and for dirty may be reset. To reset the blocked vent switch, remove the <br /> filters. access cover in the top panel of the unit heater and depress <br /> 6.Check to make sure the venting system is not damaged or <br /> the reset button located on the switch. <br /> blocked.Also check to be sure unit is venting normally and With the switch reset, turn on the electric and gas supply to <br /> that there is not negative pressure in the building adversely the unit heater and restart the unit.Carefully observe the op- <br /> affecting draft. eration of the unit to assure that it is operating correctly. If the <br /> 7.Clean heat exchanger tubes inside and out if necessary. block vent switch does not allow the unit to function, or trips <br /> after the unit has operated for a period of time,call a qualified <br /> 8.If items 1-7 do not solve the problem, check limit control service agency to service the equipment. Do not attempt to <br /> and replace if necessary.The control is accessible by removing bypass the blocked vent safety switch.Do not attempt to <br /> the left outer side panel,held in place by screws at the rear replace a defective blocked vent switch with any switch <br /> of the unit. other than that supplied by the unit heater manufacture. <br /> Page 20 <br />