JOHNSON CONTROLS
78
FORM 102.20-OM2
ISSUE DATE: 6/01/2015
SECTION 4 - SERVICE AND REPAIR
SERVICE INFORMATION
All necessary tags and decals to aid in service or to
indicate caution areas are provided. Electrical wiring
diagrams are attached to the control panel access door.
Installation, operation, and maintenance manuals are
supplied with each AHU.
This AHU offers unlimited unit access with complete-
ly removable panels. All of the AHU panels, including
the top panels, can be completely removed. Removing
the top panels allows the use of overhead cranes and
gantries to remove and service the components. Fan
and filter segments come equipped with doors.
TROUBLESHOOTING
An HVAC air system includes the AHU and the entire
air circuitry through which airflows. Included are the
following parts/assemblies:
•
Ductwork, Fittings, and Branch Ducts
•
Dampers
•
Heat Exchangers
•
Air Filters and Sound Traps
•
Coils
•
Elbows and Diffusers
•
Grilles, VAVs, and MITs
• Other items through which airflows or which of
-
fer obstruction to airflow.
While differences in temperature and humidity may
cause air movement, it may be considered very slight
compared to the positive circulation required in an air
conditioning system. To accomplish this air move-
ment, a fan performs two functions:
• Produce sufficient pressure or head to accelerate
the mass of air from a state of rest to the required
velocity.
• Produce sufficient pressure to overcome any re
-
sistances to the flow of air.
Determining these pressures is important when trou-
bleshooting an air conditioning system. The gener-
ally accepted standard instrument for measuring these
unit pressures is the pitot tube as shown in
and
. The pitot tube is used in
conjunction with an inclined manometer, magnehelic
gauge, or a tube manometer.
8 in. x D
SOLDER
D
0.02 in. DIAMETER HOLES
DRILLED THROUGH
OUTSIDE TUBE
STATIC TUBE
IMPACT
TUBE
8 in. x D
LD06362
FIGURE 80 -
CONSTRUCTION OF PITOT TUBE
When the pitot tube is used in conjunction with these
instruments, one is able to read velocity pressure (VP),
static pressure (SP), and total pressure (TP) within the
system.
LD06363
FIGURE 81 -
PITOT TUBE
PITOT TUBE
The pitot tube consists of an impact tube within a larg-
er static tube. When the impact tube is pointed directly
into the air stream, the small static pressure holes are
perpendicular to the air stream and are not affected by
air velocity as shown in
.
