VACUUM SYSTEM

TTP	B1-L3	ATA37
Cessna 172	B2-L2

 Vacuum system has a filter, vacuum gage, vacuum instruments, regulator valve, vacuum manifold, low vacuum annunciator switches, engine-driven vacuum pumps and related plumbing.
 With Garmin G1000, the source of vacuum air is in the cabin and is pulled through the system by the engine-driven vacuum pumps. This air goes through the gyro filter at the cabin inlet source before it goes through the vacuum gage and gyro instruments. The vacuum is controlled by the regulator valve. The regulator valve is on the aft side of the firewall. The vacuum air is then pulled through the vacuum manifold and past the low vacuum annunciator switches and then into the vacuum pumps.
Without Garmin G1000, vacuum pressure is measured by the low vacuum annunciator  switches in the engine compartment. The vacuum gage in the instrument panel shows the vacuum pressure.
Vacuum gage gives a direct indication of the system vacuum in inches of mercury (in.hg.).
Low vacuum annunciator switches are part of the panel annunciator warning system.
(a) If the left vacuum switch (SN012) senses a vacuum below 3.0 in.hg., the VAC annunciator will show L VAC.
(b) If the right vacuum switch (SN011) senses a vacuum below 3.0 in.hg., the VAC annunciator will show VAC R.
(c) If both switches sense a vacuum below 3.0 in.hg., the VAC annunciators will show L VAC R.
(3) For more information on the maintenance practices for the panel-mounted annunciator (UI005), 
D. On airplanes with Garmin G1000, the source of vacuum air is in the cabin and is pulled through the system by the engine-driven vacuum pump. The vacuum pressure is measured by a vacuum transducer. The air goes through the gyro filter at the cabin inlet source before it is goes through the horizon gyro indicator. The vacuum is controlled by the regulator valve. The regulator valve and the vacuum transducer are on the aft side of the firewall.

PTP Cessna 172	B1	LOC	FOT		R/I	MEL	TS
	B2		FOT		R/I	MEL	TS

371001 Vacuum System - Inspect for condition and security. B 05-12-02 120
371002 Vacuum Pumps - Check for condition and security. Check vacuum system breather

line for obstructions, condition, and security
371003 Vacuum System Hoses - Inspect for hardness, deterioration, looseness, or collapsed hoses. B 05-12-02 120
371004 Gyro Filter - Inspect for damage, deterioration and contamination. 
371006 Vacuum Manifold Check Valve - Complete a check for proper operation. (Only airplanes with dual vacuum pumps and Airborne manifolds.
371007 Do an inspection of the wear indicator ports on the vacuum pump described in the Tempest Service Letter 004.