GVZC20 Service Manual

SERVICING
30
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This minimum and maximum allowable duct static pres-
sure for the indoor sections are found in the specications
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 insu󰀩-
cient air that can cause icing of the coil. Too much air can
cause poor humidity control and condensate to be pulled o󰀨
the indoor coil causing condensate leakage. Too much air
can also cause motor overloading and in many cases this
constitutes a poorly designed system.
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To determine proper air movement, proceed as follows:
1. Using a draft gauge (inclined manometer), measure the
static pressure of the return duct at the inlet of the unit,
(Negative Pressure).
2. Measure the static pressure of the supply duct, (Positive
Pressure).
3. Add the two (2) readings together for total absolute value
of external static pressure (for example,
-0.30”wc +0.20”wc= 0.50”wc total static pressure).
CHECKING STATIC PRESSURE SINGLE PIECE AIR
HANDLER
• Measure the static pressure of the supply duct at the
outlet of the air handler
• Measure the static pressure of the return duct at the
inlet of the air handler
• Single piece air handler evaporator coil is already con
sidered in airow calculation
•  Both readings may be taken simultaneously
and read if so desired
4. Consult proper table for quantity of air.
If external static pressure is being measured on a furnace
to determine airow, supply static must be taken between
the “A” coil and the furnace.
CHECKING STATIC PRESSURE ON TWO PIECE AIR
HANDLER
• Measure the static pressure of the supply duct at the
outlet of the unit
• Measure the static pressure between the outlet of the
evaporator coil and the inlet of the air handler
• Since the evaporator coil is not part of the blower unit
or furnace, it must be not considered in calculating the
static pressure of the blower unit or furnace
•  Both readings may be taken simultaneously if
so desired
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1. Using a draft gauge (inclined manometer), connect the
positive 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.
CHECKING STATIC PRESSURE FURNACE