Johnson Controls MRC Series Installation Guide

Installation Instructions MRC

Modular Room Control (MRC) Series

Digital Thermostat

Issue Date August 14, 2002

Application

The MRC Digital Thermostat is an expandable
multi-purpose, high-quality Direct Digital Control (DDC)
illuminated thermostat designed to control virtually any
Fan Coil Unit (FCU) or Packaged Terminal Air
Conditioning (PTAC) found in hotel guestrooms. The
MRC comes standard with five relays and can be
equipped with an on-board Infrared (IR) transceiver
and Passive Infrared (PIR) motion detector. Coupled
with a magnetic door switch (wired or wireless), the
MRC becomes the brain of a highly effective Energy
Management System (EMS) for guestrooms.

When connected to the Central Interface Network
(CINET) with a pair of low voltage wires, a centrally
controlled EMS package is created. The MRC is
readily expandable to include functionality such as
humidity control, outside temperature display, mini-bar
access reporting, occupancy reporting to
housekeeping, automatic control of lights, and much
more. Use of infrared or low-voltage wiring enables
remote control of lights, occupancy reporting, and
other functions.

Installation

Locate the MRC thermostat as follows:

Mounting

The MRC is designed to be mounted on a standard
double-gang (4 x 4) junction box. If it is necessary to
mount the MRC on a single-gang box, the left side
(display side) of the MRC overlaps the wall area to the
left of the junction box.

To mount the MRC mounting plate:

1. Remove the two small screws at the base of the
MRC.

2. Pull the bottom of the back-mounting plate slightly
away from the front housing and then pull the
back-mounting plate down.

IMPORTANT: If the back-mounting plate is rotated
more than 2 or 3°, the plastic tabs at the top of the
plate may fracture or break off.

3. Attach the mounting plate to the junction box,
using the mounting screws provided with the
MRC. Ensure that the plate is mounted with the
raised arrow pointing UP (↑).

Wiring

• on a partitioning interior wall, and approximately

1.5 m (5 ft) above the floor in a location of average
temperature

• away from direct sunlight or radiant heat, outside

walls or behind doors, air discharge grills,
stairwells, or outside doors

• away from steam or water pipes, warm air stacks,

unheated/uncooled areas, or sources of electrical
interference

!

CAUTION: Risk of Shock.

Disconnect the power supply before mounting the
thermostat to prevent electrical shock or possible
damage to the equipment.

2002 Johnson Controls, Inc.

©

Part No. 24-9778-6, Rev. – www.johnsoncontrols.com

!

CAUTION: Risk of Equipment Damage.

Before applying power, make all wiring connections
and check the connections. Short-circuited or
improperly connected wires may result in permanent
damage to the unit.

IMPORTANT: Make all wiring connections in
accordance with the National Electrical Code (NEC)
and all local regulations.

To simplify installing and removing the MRC, a
standard Molex® 10-position or 8-position connector is
used. The female receptacle is on the back of the
MRC vertically centered over the high-voltage section
(see Figure 1).

1

Molex

Receptacle

Figure 1: Molex Receptacle Location

The MRC is supplied with a Molex connector prewired
with eight or ten 8 in. (203 mm) color-coded leads.
These leads are connected in the wall junction box to
the wiring from the FCU or other Heating, Ventilating,
and Air Conditioning (HVAC) device with wire nuts
(see Figure 2).

Note: For installations in which all 10 leads are not
required, the extraneous leads should be cut off at the
Molex connector.

UP

Figure 4 shows the 8-position Molex connector. It is
used with the 24 V TRIAC model MRC and comes with
8-in. wire leads. The end view of the male connector
from the wire insertion side with the pin numbers is
indicated. This is the same as looking at the female
connector point on the backside of the MRC.

12 34

6

8.7

220

5

8

7

Figure 4: 8-Pin Molex Connector Wire Lead,

in. (mm)

IMPORTANT: It is essential that the leads from

the FCU or other HVAC device be properly
connected to the male 8-pin or 10-pin connector
(see Figure 6 through Figure 10). Following each
wiring diagram is a table containing the color legend
for the 8-pin or 10-pin female receptacle (H1) at the
back of the MRC. Common industry practice for
color coding has been used, but there is no
guarantee that the same standard has been used for
the wires coming from the FCU.

Network
Harness

Molex

Connector

Figure 2: Backplate Wiring

Figure 3 shows the 10-position Molex connector with
8 in. (203 mm) wire leads, supplied with all relay
output models of the thermostat. The end view of the
male connector from the wire insertion side with the
pin numbers is indicated. This is the same as looking
at the female connector point on the backside of
the MRC.

234

8.7

220

1

6

7

89

5

10

To wire the MRC thermostat:

1. Use wire nuts to connect the wiring harness to the
FCU wires within the electrical box (see Figure 2).

2. Plug the prewired 8 or 10-pin connector into the
female receptacle at the back of the MRC.

3. Hook the tabs at the top rear of the MRC housing
into the matching depressions at the top of the
mounting plate and rotate the bottom of the
housing toward the wall until it snaps into place on
the mounting plate (see Figure 5).

4. Secure the housing to the mounting plate with the
two small screws removed in Step 1 of the
Mounting section.

Figure 3: 10-Pin Molex Connector Wire Lead,

in. (mm)

Figure 5: Returning the MRC to the Mounting Plate

2 Modular Room Control (MRC) Series Digital Thermostat Installation Instructions

Phase

Transformer

Neutral

Heat Valve

Cool Valve

Heat

Cool

H

M
L

Med

Low

Fan Motor

Relay

Fan Coil Unit

Pack

Note: In this application, the valves and fan motor
operate with the same line voltage. Therefore,
grey (valve power) and violet (fan power) wires
are connected to the red (control power) wire with a
wire nut.

Note: This drawing only reflects connections
between the FCU/PTAC and the MRC Stat.
It does not include the door switch, Network,
or other connections.

24 VAC

MRC

O

B

B

G

r

r

l

r

a

o

a

e

n

w

c

e

g

k

n

n

e

(

(

3

(

5

(

1

)

1

)

)

0
)

1 2 3 4 5

6 7 8 9 10

6

5

43

2

1

Y

B

G

W

R

V

e

l

u

l

l

e

o
w

(

4

(

)

6
)

e

i

r

h

o

e

d

i

l

y

t

e

e

(

t

2

(

8

(

(

)

7

9

)

)

)

H1

7

1098

Logic and Relays

Figure 6: 4-Pipe, 3-Speed Fan FCU with 7 Wires 24 VAC Wiring

Table 1: Pin Number Wire Color and Function

Pin Number Wire Color Function

1

2

3

4

5

6

7

8

9

10

Green Ground

Red Control Power

Black Neutral

Blue High Fan

Brown Medium Fan

Yellow Cold Water Valve

White Hot Water Valve

Grey Valve Power

Violet Fan Power

Orange Low Fan

Modular Room Control (MRC) Series Digital Thermostat Installation Instructions 3

Phase

Heat Valve

Cool Valve

H
M
L

Fan Motor

Fan Coil Unit

Note: In this application, the valves and fan motor
operate with the same line voltage. Therefore,
grey (valve power) and violet (fan power) wires
are connected to the black (control power) wire with a
wire nut.

Note: This drawing only reflects connections
between the FCU/PTAC and the MRC Stat.
It does not include the door switch, Network,
or other connections.

MRC

GREEN(1)

BLUE(10)

WHITE(3)

1 2 3 4 5

6 7 8 9

5

43

2

1

ORANGE( 5)

YELLOW(4)

7

6

VIOLET (9)

RED(6)

BLACK(2)

BROWN( 7)

GREY(8)

H1

10

1098

Figure 7: 4-Pipe, 3-Speed Fan FCU with 7 Wires 100 VAC - 277 VAC Wiring

Table 2: Pin Number Wire Color and Function

Pin Number Wire Color Function

1

2

3

4

5

6

7

8

9

10

Green Ground

Black Control Power

White Neutral

Yellow High Fan

Orange Medium Fan

Red Cold Water Valve

Brown Hot Water Valve

Grey Valve Power

Violet Fan Power

Blue Low Fan

4 Modular Room Control (MRC) Series Digital Thermostat Installation Instructions

Logic and Relays