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Model MHX3C Humidistat Installation Manual
MHX3C Locations
Specifications
RANGE: 10% to 75% RH ELECTRICAL RATING: 30 VAC, 60 VA
The MHX3C can be configured for operation as a standard humidistat, high limit humidistat, or dehumidistat. When
using this product as a standard humidistat terminals "NO" and "C" must be used. When using this product as a high
limit humidistat terminals "NO" and "C" and must be used. When using this product as a dehumidistat terminals "NC"
and "C" must be used. Use DHD3 Dial (GFI #7061) for the dehumidistat version.
WALL MOUNTING INSTRUCTIONS - Humidistat/Dehumidistat Versions
1. Chose a location for the MHX3C about five feet above the floor on an inside wall with average room
temperature and relative humidity conditions. Drill a small hole in the wall and run low voltage wiring to the
location chosen. Pull about 6” of wire through the hole.
2. Gaskets: Use the entire thin mounting gasket (both inside and outside portions) to seal the wall opening or
use foam tape to prevent drafts from affecting the humidistat operation. Do NOT install the thick gasket.
(see FIG. 1)
3. Squeeze the top and bottom of the base to release the face of the humidistat.
4. Mount the base horizontally over the wires. Attach directly to the wall, using the two screws provided in the
slotted holes.
5. Connect wires to screw terminals on the control assembly as shown in DIAGRAMS 1-5. Replace the face.
DUCT MOUNTING ON THE RETURN AIR - WALL BASE
Humidistat/Dehumidistat versions (optional)
Do not install the humidistat on the warm air duct or within 48” of UV light.
1. Locate the humidistat at least 24" upstream of the humidifier or bypass on the return air duct. Avoid areas of
direct radiation like secondary heat exchangers in the fan compartment. Cut a square hole in the duct 2-1/4”
wide and 1-3/4” tall.
2. Gaskets: Remove the inner portion of the mounting gasket and discard. Use the outer portion to seal between
the plastic base and the duct. Place the thick gasket inside the wall mount base to seal off air entering through
the vents. Line up the base with the cut out and accurately mark the holes thru the plastic duct mount plate.
(see FIG. 1)
3. Remove the humidistat and drill four 3/32” mounting holes.
4. Place the outer portion of the mounting gasket on the plastic base and mount the base with four screws. Low
voltage wire may enter the humidistat under the gasket.
5. Connect wires to screw terminals on the control assembly as shown in DIAGRAMS 1-5. Replace the face.
Wall or Duct Mount
Thin Gasket
Face
FIG. 1
WALL
MOUNT: Use
Outer & Inner Portions
DUCT
MOUNT: Use
ONLY Outer Portion
Mounting
Base
Thick Gasket
DUCT
MOUNT ONLY
