Table 6-1. TROUBLESHOOTING (cont) - TM-55-4920-416-130037

TM 55-4920-416-13

Section VI

NAVAER 17-15C-539

Paragraph 6-12

TABLE 6-1 (Cont)

TROUBLESHOOTING

TROUBLE

CAUSE

REMEDY

14. Unable to maintain adequate pressure

Loose connections.

Tighten connections properly.

when test set is connected to aircraft

pitot line or instrument line.

Leak in test line.

Fine and repair open line.

Opened or cracked instrument cases.

Replace defective instrument.

15. Unable to obtain proper pressure with

Defective pump.

Remove and replace entire pump motor

no external connections to test set.

assembly.

Loosened selector valve knob.

Tighten nut on valve shaft.

Defective selector valve.

Remove and replace valve. (Note that this

is highly unlikely. Do not replace until all

other possibilities have been carefully

checked.)

16. Unable to reach or maintain maximum

Leaky instrument.

Perform case leak tests in accordance with

reading

altimeter,

airspeed

procedures given in Section IV.

indicator, or manifold pressure gauge.

instrument leaks, replace it.

Improperly adjusted relief valves.

Reset

relief

valves.

(Refer

paragraph 6 -12.)

NOTE

If instruments do not reach designated upper limit of test setting on VPT-7A tester, this may

be due to relief valve setting adjusted too low for present barometric pressure. (Original

setting may have been made when barometric pressure was high at factory.)

6-12. RESETTING THE RELIEF VALVES. The spring

particular instrument in Section IV.

settings in the relief valve may have to be reset. Access to

c. Turn the stems of the appropriate relief valve so that it

these valves is through the front door.

Resetting is

relieves somewhat below the point desired.

accomplished by a screwdriver when resetting the vacuum

relief valves and a socket head wrench when resetting the

NOTE

pressure relief valves.

a. Set the appropriate SELECTOR VALVE to the

The pressure relief valve stems are

position for checking the instrument which needs resetting of

secured in position with a lock nut. The

the relief valve.

vacuum pressure relief valve stems are

b. Slowly manipulate the VACUUM and PRESSURE

secured internally at the set positions.

control valves as required and outlined under Operation of the