GeneralAire MHX3 User Manual
R
MHX3
Manual humidistat/dehumidistat
control
FIG. 1
WALL MOUNT VERSION
I. SAFETY
WARNING! Improper electrical wiring can result in fire,
failure or loss of humidity control. Disconnect electrical
power before installing and servicing. Failure to disconnect
electrical power may result in injury or death. All local
building and electrical codes must be followed.
The MHX3 humidistat must be installed by a qualified technician.
Failure to properly install the MHX3C may result in property
damage or personal injury.
Homeowners must read instructions and understand the operation
of the MHX3 and the humidifier(s) it controls.
Improper operation can result in over or under humidification.
Over humidification can result in condensation, structural damage
and mold. Condensation within a building's structure can cause
loss of structural strength. Condensation can also enable mold
and mildew growth resulting in personal injury and damage to
building structure and contents.
Safety questions regarding the MHX3 may be directed to General
Filters, Inc. Toll free (866) 476-5101
II. APPLICATION
The MHX3 control provides low voltage control of most
humidifiers. The humidistat uses a SPDT switch and is designed
for wall mounting in the living area or mounting on the return air
duct.
RANGE: 10% to 85% RH ELECTRICAL RATING: 30 VAC, 60 VA
OPERATING MODES
The MHX3 can be configured for operation as a standard
humidistat or dehumidistat. When using this product as a
standard humidstat terminals C and NO must be used. Use MHX3
face plate for the humidistat version. When using this product as a
dehumidistat terminals C and NC must be used. Use DHX3 face
plate for the dehumidistat version.
III. INSTALLATION INSTRUCTIONS - PRECAUTIONS
The installer must be a qualified technician. Disconnect electrical
power before begining installation. Do not install the humidistat
on the warm air duct. Conduct a thorough checkout before leaving
the installation.
WALL MOUNT INSTRUCTIONS - Humidistat/Dehumidistat
versions
1. Choose a location for the MXH3 about five feet above the floor
on an inside wall with average room temperature and relative
humidity conditions.
2. Drill a small hole in the wall and run low voltage wiring to the
location chosen. Pull about 6” of wire through the hole.
Use the entire mounting gasket (both inside and outside
portions) to seal the wall opening or use foam tape to prevent
drafts from affecting the humidistat operation. (see fig 3.)
3. Remove the knob on the humidistat. 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 the wires to the screw terminals on the control assembly
as shown in wiring DIAGRAMS 1-5 Replace face and Knob.
RESIDENTIAL AIR TREATMENT PRODUCTS
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 exchanger in the fan compartment.
2. Cut a square in the duct 2-1/4” wide and 1-3/4” tall. Remove the
inner portion of the mounting gasket and discard. Use the outer
portion to seal between the plastic base and the duct. Line up the
base with the cut out and accurately mark the holes thru the plastic
duct mount
plate. (see fig 3.)
3. Revove the humidistat and drill four 3/32” mounting holes.
4. Place the outer portion of the mounting gaskets 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 wiring DIAGRAMS 1-5. Replace the face and knob.
DUCT MOUNTING ON THE RETURN AIR - DUCT BASE
Humidistat/Dehumidistat versions (recommended)
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 exchanger in the fan compartment.
2. Remove face by inserting screwdriver into the pry slot and
twisting (see fig. 2)
3. Use the plastic duct mount plate as a template. Accurately mark
and drill the (4) 3/32” mounting holes and cut away the 4-1/4” x 2-1/2”
section of the duct mount plate.
4. Place duct mount base gasket on the humidistat base and mount
the base with four screws. Low voltage wire may enter the humidistat
under the gasket (see fig. 2)
5. Connect wires to screw terminals on the control assembly as shown in
wiring DIAGRAMS 1-5. Replace face and knob.
MHX3 CALIBRATION INSTRUCTIONS
(Accurate humidity gauge required)
1. Use an accurate humidity gauge to determine the current relative
humidity in the room where the humidstat is located. This relative
humidity will be used in step 5.
2. Remove the face plate from the housing.
3. Turn the knob on the MHX3 faceplate to the “on” position
4. Very slowly, turn the knob clockwise until you hear a “click” from
the humidistat control and leave the knob in this position.
5. Turn the ring (not the knob) so that the knob is pointed directly
at the current relative humidity number determined in STEP 1.
6. The humidistat in now calibrated to match you humidity gauge.
WARNING! Do not set relative humidity too high during cold
weather. Over humidification can result in condensation,
structural damage and mold. Condensation within a building's
structure can cause loss of structural strength. Condensation
can also enable mold and mildew growth resulting in personal
injury and damage to building structure and contents.
TROUBLESHOOTING -- Humidistat Version
SYMPTOM
Humidifier turns
on and off
repeatedly
Humidifier
operates
continuously
No humidifier
operation in “ON”
mode
Ideal humidity is
not achieved
1. If mounted on wall, verify wire clearance hole in wall is sufficiently
insulated to preven drafts from affecting the humidistat.
2. If mounted on return air duct, verify humidistat is at least 24”
upstream of humidifiers air discharge.
1. When the humidity in the home is less than the knob setting on
the humidistat the stat will operate the humidfier until the humidity
is higher. Reduce knob setting.
2. Verify function of solenoid valve.
1. Set the thermostat to operate both furnace burner and blower.
Operation may be necessary for system power.
2. Verify terminals 2 and 3 are used on the humidistat. These are the
contacts for humidification.
3. Check voltage at at terminals 2 and 3. There should be no voltage
for an Elite Steam or 1137/1000 power humidifier. Voltage should
be 20-30 VAC from most others.
4. Verify humidifier operation by bypassing the humidistat.
1. Technical fault with humidifier. Check water supply, electrical
connnections and condition of the evaporator pad. Verify metering
orifice at the solenoid valve is not obstructed.
2. Humidifier run time is too short. Switch water supply to hot water if
appropriate (use copper tubing).
3. Excess air infiltration. Seal sources of air loss.
4. Humidifier is undersized. Switch water supply to hot water if
appropriate (use copper tubing). Add additional unit(s) or
replace existing unit with a larger unit.
DIAGNOSTIC STEPS
WIRING DIAGRAMS
DIAGRAM 1 WIRING 24V. BYPASS HUMIDIFIER
NC
C
NO
HMX3
Humidistat
24 V. TRANSFORMER
(OMIT IF POWER SUPPLY
IS 20-30 VAC)
120V. POWER SUPPLY
SWITCHED WITH FURNACE OPERATION
DIAGRAM 2
HUMIDIFIER CONTROL LEADS
110V SWITCHED WITH
FURNACE HEATING CYCLE
WIRING HIGH LIMIT HUMIDISTAT WITH ELITE STEAM HUMIDIFIER
N2
GND
N1
AB
AB
GND
IN
NO
C
NC
C
NO
CONTROL MODULE
STEAM HUMIDIFIER
GND
24V
DIAGRAM 3 WIRING 120V. 1137/1000 POWER HUMIDIFIER
(YELLOW WIRES)
HUMIDISTAT
NC
C
NO
USE TERMINALS C AND NO
FOR HUMDISTAT
110V SWITCHED WITH FURNACE HEATING CYCLE
DIAGRAM 4
HUMIDIFIER CONTROL LEADS
L1 N
DIAGRAM 5
USE TERMINALS C AND NC FOR DEHUMDISTAT
WIRING 120V. 1137/1000 POWER HUMIDIFIER
(YELLOW WIRES)
HUMIDISTAT
NC
C
NO
FIELD SUPPLIED RELAY
24V COIL, N.O. 5A MIN.
727-58
24 V. TRANSFORMER
(OMIT IF POWER
SUPPLY IS 20-30 VAC)
NC
USE TERMINALS C AND NO FOR HUMDISTAT
727-58
NO
USE TERMINALS C AND NO FOR HUMDISTAT
HUMIDIFIER
POWER CORD
L1 N
110V CONSTANT VOLTAGE
1300 DEHUMIDIFIER
HUMIDISTAT
NO
HUMIDIFIER 24V AUX POWER
(RED WIRES)
G
HUMIDIFIER
POWER CORD
G
USE TERMINALS C AND NO FOR HUMDISTAT
N
L1
C
HUMIDISTAT
HUMIDIFIER 24V.
SOLENOID VALVE
OR 24V. DRUM MOTOR
NC
C
(NOT USED, ATTACH WIRE
NUTS TO EACH LEAD)
DO NOT TOUCH TOGETHER!
HUMIDIFIER 24V AUX POWER
(RED WIRES)
(NOT USED, ATTACH WIRE
NUTS TO EACH LEAD)
DO NOT TOUCH TOGETHER!
GENERALAIRE 1300
DEHUMIDIFIER
DH
D
Y
W
C
G1
G2
S1
S2
FORM NO MHX3-06 REV C
Product Information:
Serial Number: _____________________________________________________________
Model: ____________________________________________________________________
Install Date: Month _______________ Day ______________ Year _____________
Owner Information:
Name: _____________________________________________________________________
Address: ___________________________________________________________________
Address 2: __________________________________________________________________
City: _______________________ State: ___________ Zip Code: ____________________
Phone: _____________________________________________________________________
Email: ______________________________________________________________________
WARRANTY REGISTRATION
Contractor Information:
Contractor Name: _____________________________________________________________
Address: ____________________________________________________________________
Address 2: ___________________________________________________________________
City: _____________________ State: ___________ Zip Code: _______________________
Contractor Phone: ____________________________________________________________
Contractor Email: _____________________________________________________________
You may register online at www.GeneralAire.com or mail form below
Mail Form To:
General Filters, Inc
Attn: Warranty Dept.
43800 Grand River Ave.
Novi, MI 48375
Fresh Indoor Air Quality
R
cut along dashed line
cut along dashed line
USA CUSTOMERS
General Filters, Inc.
43800 Grand River Ave.
Novi, MI 48375
www.GeneralAire.com
Engineering@generalfilters.com
Toll Free (866) 476-5101
CANADIAN CUSTOMERS
Canadian General Filters, Ltd.
400 Midwest Rd.
Toronto, ON M1P3A9 Canada
www.CGFProducts.com
Sales@cgfproducts.com
Tel. (416) 757-3691
TECHNICAL SUPPORT
FORM NO MHX3-06 REV C
USE BOTH WITH
WALL MOUNTING
USE WITH DUCT
MOUNTING ONLY
USE OUTSIDE
PORTION ONLY
WITH DUCT
MOUNTING
GASKET PLACEMENT
FIG. 3
DUCT MOUNT
VERSION
FIG. 2
DUCT MOUNT BASE
MHX3-11
DUCT MOUNT BASE
GASKET
SCREWDRIVER PRY SLOT
WALL MOUNT BASE
(CAN MOUNT ON DUCT
WITH GASKETS SHOWN)
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