VCCS Controls and Indicators

STUDENT GUIDE FOR T-1A AIRCRAFT SYSTEMS

CHAPTER SEVEN

Pressurization control subsystem

Electric Heat Subsystem (EHS)

VCCS

The VCCS provides preflight, in-flight, and postflight air conditioning for the flight deck and

avionics rack exhaust.

The VCCS is the only source of cooling when the aircraft's engines are not operating. It is also

the backup cooling source when the ACU is not operational. The VCCS operates on 28 VDC

external ground power when the engines are not operating and the right nonessential bus when

the engines are operating.

VCCS Controls and Indicators

The AUX TEMP CONTROL switch group on the environmental control panel controls VCCS

operation.

AUX COOL - Supplies electrical power to the VCCS compressor.

GND AIR - Supplies electrical power to the fresh air blower motor when the landing gear

ground safety relay is engaged. Power is also supplied to the pressurization control vacuum

pump and solenoid valve to open the outflow safety valves.

AV STBY BLO - Supplies electrical power to the avionics rack refrigerant shutoff

solenoid valve when the AUX TEMP CONTROL switch is in the AUX COOL position. The

valve deenergizes, stopping refrigerant flow to the avionics rack evaporator. In this condition

flight deck cooling is maximized.

ACU Subsystem

The ACU provides heating, cooling, and pressurization when the engines are operating. The

ACU is capable of maintaining the cabin temperature between 60-90 degrees Fahrenheit (F) at

all ambient temperatures up to and including the service ceiling.

ACU Controls and Indicators

Reference the ACU diagram in the T.O. 1T-1A-1.

Bleed Air Selector

OFF - Ram air is supplied to the cabin in flight. VCCS cooling air is available, bleed air is

unavailable.

ENVIRONMENTAL CONTROL SYSTEMS 7-3