McQuay MT 155 Maintenance Manual
Installation and Maintenance Manual IM 1014
MT 155 Thermostat
Installation
DANGER
READ THESE INSTRUCTIONS CAREFULLY BEFORE
ATTEMPTING TO INSTALL, OPERATE OR SERVICE THIS
THERMOSTAT.
Failure to observe safety information and comply with
instructions could result in PERSONAL INJURY, DEATH AND/
OR PROPERTY DAMAGE.
To avoid electrical shock or damage to equipment, disconnect
power before installing or servicing. Use only wiring with
insulation rated for full thermostat operating voltage. Use
copper wire only. Insulate or wirenut all un-used leads. Any
wiring, including the remote probe,may carry the full operating
voltage of the thermostat.
To avoid potential fire and/ or explosion do not use in
potentially flammable or explosive atmospheres.
Retain these instructions for future reference. You must review
your application and national and local codes to ensure that
your installation will be functional and safe.
1 Install the thermostat with the two furnished mounting
screws to a standard 2" x 4" electrical box, 4-11/16" x 21/8" square device box with a 2" x 4" adapter ring or to a
4" x 4" box with accessory adapter plate.
2 For wall installations, mount the thermostat on an inside
wall approximately 5 feet above the floor. The location
should provide circulation at average room temperature.
Avoid direct sunlight or sources of hot or cold air in the
room or wall.
3 Remove the knob and then the cover. Mount thermostat
base assembly to the outlet box using the screws
provided, tighten the screws evenly but do not over
tighten. Make wiring connections as noted.
4 To use a remote sensor, remove jumper JP-1 to disable
local sensing. See Figure 1. Failure to remove JP-1 when
using a remote sensor will cause improper operation of
the thermostat. Some units do not have remote sensing
capability . See Application Notes.
Group: Applied Air Systems
Part Number: 910102989
Date: August 2009
Figure 1: Removing Jumper JP-1
INSTALL COVER
LOCKING SCREW
REMOVE JP1
WHEN USING A
REMOTE SENSOR
5 Reinstall the cover assembly. Install cover locking screw
JP1
provided. Reinstall the knob.
6 Checkout: After wiring and installation are complete,
energize the system and check the operation. Adjust the
thermostat as necessary to complete at least one cycle.
Be sure the thermostat and all other equipment are
functioning correctly.
Thermostat Operation
Temperature Range: 50°F - 90°F (10°C - 32°C)
TA155: A HEAT-OFF-COOL system switch manually selects
heating or cooling mode. In the HEAT position, only the heat
output cycles with demand. In the COOL position, only the
cool output cycles with demand. In the OFF position, heating
and cooling outputs are off. Units with a two position system
switch or without a system switch must use a load transfer
switch when both heating and cooling outputs are used. This
prevents control failure and equipment damage caused by
direct cycling between loads.
TB155: An ON-OFF system switch enables auto-changeover
of heating and cooling modes. In the ON position the
thermostat activates heating or cooling outputs dependant
upon the relationship between set point and ambient
temperature. Heat on to cool on dead band is 4°F. In the OFF
position, heating and cooling outputs are off. Units without a
system switch cycle between heating and cooling with a 4°F
dead band.
IM 1014 / Page 1 of 2 © 2009 McQuay International 800-432-1342 www.mcquay.com
FAN: Some units have a switch for manual selection of fan
speed. On these units fan operation is either internally wired
for fan continuous operation or is dependant upon connection
1
2
3
1
2
5
1
2
3
4
TB1
TB2
TB3
NO CONNECTION
L2 or NEUTRAL
TB1-3
TB1-4
FAN
COOL
OUTPUT
HEAT
OUTPUT
TB2-3
FAN HIGH
FAN LOW
FAN MED
L1
FAN SUPPLY
TB2-2
TB2-1
TB2-4
TB2-5
TB3-3
CONNECT
FOR FAN
CONTINUOUS
TB3-2
TB3-1
SWITCHED POWER
COOL
OUTPUT
HEAT
OUTPUT
1
2
3
1
2
TB1
TB3
L1
TB3-3
TB3-2
TB3-1
NO CONNECTION
L2 or NEUTRAL
TB1-3
TB1-4
to the fan supply input . When internally wired for fan
continuous operation, the fan will be off when the system
switch is off. When dependant upon external connections the
fan may not be off with the system switch in the off position.
The fan supply input is switched to fan speed outputs (HI MED - LO).
SWITCHED POWER: L1 power is switched to this output any
time the system switch is out of the OFF position.
Ratings
Table 1: Fan and system switches
Voltage
Rating
Inductive
FLA LRA
24 VAC N.A. N.A. N.A. 24 VA 10 VA
120 5.8 34.8 6.0 125 VA 20 VA
240 2.9 17.4 5.0 125 VA 20 VA
277
2.4 14.4 4.2 125 VA 20 VA
Resistive
Amps
Pilot
Duty
Wire Lead Colors (if applicable)
White with Orange Stripe Fan High
White with Red Stripe Fan Med.
White with Brown Stripe Fan Low
Red Heat
Blue Cool
Black L1
Yellow L2 or Neutral
Orange Switched Power
Violet Fan Supply
Brown Remote Probe
Brown Remote Probe
Application Notes
1 To use a remote sensor, remove jumper JP-1 to disable
local sensing. See Figure 1. Failure to remove JP-1 when
using a remote sensor will cause improper operation of
the thermostat. Some units do not have remote sensing
capability.
2 Units with remote sensing capability have a four-position
terminal block at TB1. If TB1 is two position the unit is
local sensing only.
3 Remote probe wiring should be located away from any
electrical motors or power wiring
4 Some units are internally wired for permanent fan
continuous operation.
5 On units with a Fan Supply input, the operation of the
fan is determined by wiring connection. For fan
continuous, jumper the Fan Supply input (TB2-5) to the
Switched Power output (TB3-3).
6 For fan cycling operation with a call for heat or cool, a
fan relay must be used.
© 2009 McQuay International 800-432-1342 www.mcquay.com IM 1014 / Page 2 of 2
Thermostatic
Switching
7 Observe electrical ratings. Thermostatic outputs are pilot
duty only.
Wiring Diagrams
Figure 2: Units with remote sensing capability
TB3-1
HEAT
OUTPUT
TB3-2
TB3
1
2
TB3-3
3
TB2-1
TB2
1
L2 or NEUTRAL
NO CONNECTION
REMOTE PROBE 1
REMOTE PROBE 2
TB1-4
TB1-3
TB1-2
TB1-1
4
3
2
1
TB1
TB2-2
2
TB2-3
3
4
TB2-4
5
TB2-5
Figure 3: Units with switches used for local sensing only
Figure 4: Units with no switches with local/remote sensing
capability
TB3
1
2
3
L2 or NEUTRAL
NO CONNECTION
REMOTE PROBE 1
REMOTE PROBE 2
TB1-4
TB1-3
TB1-2
TB1-1
4
3
2
1
TB1
Figure 5: Units with no switches used for local sensing
only
COOL
OUTPUT
SWITCHED POWER
L1
FAN H IGH
FAN MED
FAN L OW
FAN SUPPLY
TB3-1
TB3-2
TB3-3
FAN
HEAT
OUTPUT
COOL
OUTPUT
CONNECT
FOR FAN
CONTINUOUS
L1
5
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