PROBLEM PROBABLE CAUSE
SOLUTION
TROUBLE SHOOTING GUIDES
FANS
Coils a. Dirty or clogged
Obstructed Fan Inlets a. Elbows, cabinet walls or other obstructions restrict
air flow. Inlet obstructions cause more restrictive
systems but do not cause increased negative
pressure readings near the fan inlet(s). Fan speed
may be increased to counteract the effect of
restricted fan inlet(s)
No Straight Duct at Fan Outlet a. Fans which are normally used in duct system are
tested with a length of straight duct at fan outlet. If
there is no straight duct at the fan outlet, decreased
performance will result. If it is not practical to
install a straight section of duct at the fan outlet,
the fan speed may be increased to overcome
this pressure loss.
Obstructions in High Velocity a. Obstruction near fan outlet
Air Stream b. Sharp elbows near fan outlet
c. Improperly designed turning vanes
d. Projections, dampers or other obstructions in part
of system where air velocity is high
CFM High - Too Much System a. Oversized duct work
Air Flow b. Access door open
c. Registers or grilles not installed
d. Damper set to by-pass coils
e. Filter(s) none in place
f. System resistance much lower than anticipated
Fan a. Fan speed too fast
Incorrect Static Pressure System, Fan or Interpretation General Discussion:
of Measurements The velocity pressure at any point of measurement
is function of the velocity of the air or gas and its density
The static pressure measured in a "loose" or oversized
system will be less than the static pressure in a
"tight" or undersized system for the same air flow rate
Incorrect Static Pressure In most systems, pressure measurements are indicators
- Continue - of how the installation is operating. These
measurements are the result of air flow and as such are
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