GeneralAire G-99 User Manual

Model G-99 Air Filter Gage

Installation Manual

General Filters, Inc. 43800 Grand River Ave., Novi, Michigan 48375 •

Phone: [phone] • Fax [phone] • www.generalaire.com

ApplicAtion

The G-99 Air Filter Gage provides a visual indication of the need to replace the air filters in forced
air heating and cooling systems. The gage is installed between the blower and the filter where
a slight vacuum exists due to the air flow resistance of the air filter. Air flowing into the gage,
around the calibration screw, lifts a vane in proportion to the negative pressure in the blower
compartment. As the air filter loads, the vacuum increases, raising the vane to indicate a filter
change is necessary.

The gage may be calibrated in a negative pressure range from 0.1 to 0.4 inch w.c. When
properly calibrated in this range a vacuum increase of 0.10 to 0.15 inch w.c. will indicate a filter
change is necessary.

precAutions

The installer should be an experienced service technician. When drilling the hole in the blower
compartment extreme care should be taken not to damage components within the heating or
cooling system.

Toll Free [phone]

instAllAtion

The gage must be located where it can sense pressure conditions
in the blower compartment between the filter and the blower.
Select a location on a vertical surface enclosing the blower
compartment and drill a 3/8" hole. Remove the protective paper
from the foam adhesive strip on the back of the gage. Mount the
gage in a level position with the pressure sensing tube projecting
into the blower compartment.

The gage may be remote mounted with a maximum length
of 10 feet of 5/16 inch inside diameter vinyl tubing. Order
remote Kit part No. G99-14

RETURN

AIR

AIR

FILTER

GAGE

BLOWER

General Filters, Inc. 43800 Grand River Ave., Novi, Michigan 48375 •

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G99-1 GAGE HOUSING

G99-2 GAGE COVER

G99-3 FILTER SCREEN

G99-4 VANE

G99-7 PIN

G99-12 DIAL PLATE

G99-8
RETAINER CLIP

G99-9
CALIBRATION SCREW

G99-11 FOAM ADHESIVE STRIP - NOT SHOWN

U.S. PAT. 6190442

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Phone: [phone] • Fax [phone] • www.generalaire.com

cAlibrAtion

Install a clean filter and run blower on highest speed.
With a small screwdriver adjust the calibration screw, on
the face of the gage, to put the pointer in the clear area
in the center of the blue "FILTER IS CLEAN" range.

operAtion

As the air filter begins to clog the pointer will move up
in the gage. When the pointer moves into the black
"CHANGE FILTER" range a clean filter should be
installed.

Model G-99 Air Filter Gage

Installation Manual

Toll Free [phone]

service

The gage may be disassembled for service although this should rarely be required since it
contains a small filter screen to stop dust from entering the area of the vane. Remove gage
and, from the back, push white plastic clips out with a blunt tool. Remove calibration screw,
lift off clear cover and dust all parts with a clean brush. Reassemble and test that the vane
moves freely in the gage. A fresh adhesive strip may be required to reinstall.

pArts list

WHEN ORDERING PARTS, REFER TO THE ABOVE LIST OF PARTS NAMES AND PARTS NUMBERS

General Filters, Inc. 43800 Grand River Ave., Novi, Michigan 48375 •

Phone: [phone] • Fax [phone] • www.generalaire.com

Toll Free [phone]