TM 1-1520-240-102-10-1SECTION X. HEATING, VENTILATION, COOLING, AND ENVIRONMENTALCONTROL SYSTEMS2-10-1. Heating and Ventilating System.A 200,000 btu/hr capacity internal combustion heatingsystem is provided. it consists of a heater unit, a fuelcontrol unit, an ignition assembly, a blower, control re-lays, and air pressure and temperature control circuits.Ducting carries heated air or ventilating air to the cockpitand the cabin. The heater consumes approximately 15pounds of fuel per hour from the right main fuel tank.The heater and blower are mounted vertically on the rightside of the helicopter, immediately aft of the forward cab-in section bulkhead. Air for the system is provided by theblower which draws air from an inlet on the forward upperside of the fuselage. If sufficient air is not available forproper heater operation, an automatic differential pres-sure switch in the heater circuit will stop the heater.Both ventilating and combustion air enters the heaterinlet. The heating air passes over the heated metal wallsof the combustion chamber and is directed to a networkof ducting. The air entering the combustion chamber iscombined with atomized fuel and, after combustion thatheats the metal walls, the exhaust is discharged throughan outlet on the forward upper side of the fuselage. Pow-er to operate the blower is supplied by the No. 2 AC busthrough the CABIN HEATER BLOWER circuit breaker onthe No. 2 PDP. Power to the rest of the system is suppliedby the No. 2 DC bus through the CABIN HEATER CONTcircuit breaker on the No. 2 PDP.2-10-2. HTG Panel.The HTG (heating) panel (fig. 2-10-1) is located on theoverhead switch panel (fig. 2-1-10). It consists of a rheo-stat-type CABIN TEMP SEL rotary switch, a three-posi-tion heater function switch, and a spring-loaded push-buttton HTR START switch.a.CABIN TEMP SEL Rotary Switch. The CABINTEMP SEL rotary switch is labeled COOL and WARM.This switch operates in conjunction with the temperaturecontroller relay in the heater circuit and with a cabin ther-mostat. One set contacts on the temperature controllerrelay closes to complete a circuit to the fuel control sole-noid valve. This allows fuel to be delivered to the heater.The second set of contacts on the temperature controllerrelay closes to complete the circuit to the heater windingsin the cabin thermostat. The heater windings heat a col-umn of mercury in the thermostat, causing it to rise.When the mercury column reaches a 34_C contact, thetemperature control relay is shunted, causing its contactsto open and interrupt the circuit to the fuel control sole-noid valve. This stops heater operation by shutting off thefuel supply to the heater.Figure 2-10-1. HTG PanelThe circuit to the thermostat heater winding is also inter-rupted, allowing the winding to cool and the mercurycolumn to contract, thus reenergizing the temperaturecontroller relay. this creates a cycling effect, the rate ofwhich can be varied by increasing or decreasing theresistance between the temperature selector and hethermostat heating winding. Resistance is varied by turn-ing the CABIN TEMP SEL rotary switch. this increase ordecrease in resistance directly varies the time the heateris allowed to operate before being automatically cycled.b.Heater Function Switch. The heater functionswitch is labeled BLWR ONLY , OFF, and HTR ON. Theswitch selects the desired feature of the heating andventilating system. When the switch is set to BLWRONLY, the blower forces unheated air into both the cock-pit and cabin. Further movement of the heater controls isnot required. Selecting HTR ON energizes the variousunits of the heater once the HTR START switch is pres-sed. The heating and ventilating system is shut downwhen the switch is set to OFF.c.HTR START Switch. When HTR ON is selectedon the heater function switch and the HTR START switchis pressed, the heater control circuits are energized. The
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business
