Overtemperature Warning System

CHAPTER TWENTY

T-34C AIRCRAFT SYSTEMS FAMILIARIZATION

WORKBOOK

System Component Function

The function of each system component in each of the three control lever positions is illustrated

in the table below.

Control Lever Position

Firewall Gate Valve

Butterfly Valve

Bleed Air Regulator

OFF

Closed

Full open

Closed

FRESH AIR

Progressively opens

Full open

Closed

INCREASE

TEMPERATURE

Full open

*Progressively

INCREASE

closes

opens

*With the cockpit environmental control lever in the full forward position in the

TEMPERATURE INCREASE range, the butterfly valve is fully closed and the bleed air

regulator is full open. The cockpit will be receiving only bleed air with no outside air mixed.

Overtemperature Warning System

An overtemperature sensor located in the air duct aft of the firewall provides a warning of

overtemperature in the duct area. If the air duct temperature reaches 250 F, an electrical signal

from the sensor will cause the MASTER CAUTION and BLEED AIR annunciator fault light in

each cockpit to illuminate. Placing the environmental control lever in FRESH AIR INCREASE

should extinguish the lights.

Aft Cockpit Ventilation

In addition to the ventilation provided by the cockpit environmental control system, the aft

cockpit can receive additional outside fresh air via a ram air inlet on the underside of the fuselage

(beneath the front cockpit) which directs ram air to the air outlets on the center console in the aft

cockpit. Control of the system is provided through a push-pull knob on the aft cockpit center

console labeled OUTSIDE AIR, PULL ON. With the knob pushed in, no air flows from the air

outlets. Pulling the knob to ON opens a valve and air flows from the air outlets. Air flow and

direction is controlled by the louvers on the air outlets. The center console also houses the

evaporator for the air conditioning system. If the air conditioning system is on, the outside air

entering this system is also cooled.

Windshield Defogging System

A WINDSHIELD DEFOGGER control lever located above the cockpit environmental control

lever provides the pilot in the front cockpit with control of air flow to remove condensation from

the inside surface of the windshield. The lever controls the defogger valve located aft of the

firewall in the cockpit air ducting. In the OFF position the valve is closed and no air flows.

Forward movement of the lever progressively toward MAX opens the valve to permit increasing

air flow to the windshield. The most effective windshield defogging is achieved with the

defogger control at MAX and the cockpit environmental control in the TEMPERATURE

INCREASE range.

20-4 COCKPIT HEATING, VENTILATING, AND WINDSHIELD DEFOGGING SYSTEM