Service Manual

SERVICING
120
S-202 DUCT STATIC PRESSURES AND/OR STATIC PRES-
SURE DROP ACROSS COILS
This minimum and maximum allowable duct static pressure for
the indoor sections are found in the specifications section.
Tables are also provided for each coil, listing quantity of air
(CFM) versus static pressure drop across the coil.
Too great an external static pressure will result in insufficient air
that can cause icing of the coil. Too much air can cause poor
humidity control and condensate to be pulled off the evaporator
coil causing condensate leakage. Too much air can also cause
motor overloading and in many cases this constitutes a poorly
designed system.
S-203 SINGLE PIECE AIR HANDLER EXTERNAL STATIC
To determine proper airflow, proceed as follows:
1. Using a Inclined Manometer or Magnehelic gauge , measure
the static pressure of the return duct at the inlet of the air
handler, this will be a negative pressure (for example-.30"wc)
2. Measure the static pressure of the supply duct at the outlet
of the air handler, this should be a positive pressure (for
example .20"wc).
3. Add the two readings together (for example -.30"wc + .20"wc
= .50"wc total external static pressure.
NOTE: Both readings may be taken simultaneously and read
directly on the manometer if so desired.
4. Consult proper air handler airflow chart for quantity of air
(CFM) at the measured external static pressure.
+ .20” wc
- .30” wc
S-203A TWO PIECE AIR HANDLER EXTERNAL STATIC
PRESSURE
To determine proper airflow, proceed as follows:
1. Using a Inclined Manometer or Magnehelic gauge, measure
the static pressure between the outlet of the evaporator coil
and the inlet of the air handler, this will be a negative pressure
( for example -.30"wc)
2. Measure the static pressure of the supply duct at the outlet
of the unit, this should be a positive pressure (for example
.20"wc).
3. Add the two readings together (for example -.30"wc + .20"wc
= .50"wc total static pressure.
NOTE: Both readings may be taken simultaneously and read
directly on the manometer if so desired.
4. Consult proper air handler airflow chart for quantity of air
(CFM) at the measured external static pressure.
Supply Static
+ .20” wc
Return Static
- .30” wc
S-204 COIL STATIC PRESSURE DROP
1. Using a draft gauge (inclined manometer), connect the posi-
tive probe underneath the coil and the negative probe above
the coil.
2. A direct reading can be taken of the static pressure drop
across the coil.
3. Consult proper table for quantity of air.
STATIC PRESSURE DROP
If the total external static pressure and/or static pressure drop
exceeds the maximum or minimum allowable statics, check for
closed dampers, dirty filters, undersized or poorly laid out duct
work.