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368261-UIM-B-1008

Johnson Controls Unitary Products

5

SECTION II: DUCTWORK

DUCTWORK GENERAL INFORMATION

The duct system’s design and installation must:

1.

Handle an air volume appropriate for the served space and within
the operating parameters of the furnace specifications.

2.

Be installed in accordance of National Fire Protection Association
as outlined in NFPA standard 90B (latest editions) or applicable
national, provincial, state, and local fire and safety codes.

3.

Create a closed duct system. For residential and Non-HUD Modu-
lar Home installations, when a furnace is installed so that the sup-
ply ducts carry air circulated by the furnace to areas outside the
space containing the furnace, the return air shall also be handled
by a duct(s) sealed to the furnace casing and terminating outside
the space containing the furnace.

4.

Complete a path for heated or cooled air to circulate through the
air conditioning and heating equipment and to and from the condi-
tioned space.

When the furnace is used with a cooling coil, the coil must be installed
parallel with, or in the supply air side of the furnace to avoid condensa-
tion in the primary heat exchanger. When a parallel flow arrangement is
used, dampers or other means used to control airflow must be ade-
quate to prevent chilled air from entering the furnace. If manually oper-
ated, the damper must be equipped with means to prevent the furnace
or the air conditioner from operating unless the damper is in full heat or
cool position.

When replacing an existing furnace, if the existing plenum is not the
same size as the new furnace then the existing plenum must be
removed and a new plenum installed that is the proper size for the new
furnace. If the plenum is shorter than 12” (30.5 cm) the turbulent air flow
may cause the limit controls not to operate as designed, or the limit con-
trols may not operate at all.

The duct system is a very important part of the installation. 

If the duct

system is improperly sized the furnace will not operate properly.

The ducts attached to the furnace plenum, should be of sufficient size
so that the furnace operates at the specified external static pressure
and within the air temperature rise specified on the nameplate.

If a matching cooling coil is used, it may be placed directly on the fur-
nace outlet and sealed to prevent leakage. If thermoplastic evaporator
‘A’ coil drain pans are to be installed in the upflow/horizontal configura-
tion, then extra 2” minimum spacing may be needed to ensure against
drain pan distortion.

DUCT FLANGES

Four flanges are provided to attach ductwork to the furnace. These
flanges are rotated down for shipment. In order to use the flanges,
remove the screw holding an individual flange, rotate the flange so it is
in the upward position and reinstall the screw then repeat this for all 4
flanges.

If the flanges are not used, they should remain in the rotated down posi-
tion as shipped.

DUCTWORK INSTALLATION AND SUPPLY PLENUM 

CONNECTION - UPFLOW/HORIZONTAL

Attach the supply plenum to the furnace outlet. The use of
an approved flexible duct connector is recommended on all
installations. This connection should be sealed to prevent
air leakage. The sheet metal should be crosshatched to
eliminate any popping of the sheet metal when the indoor
fan is energized.

FLOOR BASE AND DUCTWORK INSTALLATION - 

DOWNFLOW

Installations on combustible material or directly on any
floors must use a combustible floor base shown in Figure 2.
Follow the instructions supplied with the combustible floor
base accessory. This combustible floor base can be
replaced with a matching cooling coil, properly sealed to
prevent leaks. Follow the instructions supplied with the
cooling coil cabinet for installing the cabinet to the duct con-
nector. Plug intake and vent pipe holes in bottom panel and
move grommet to desired vent side exit.

Downflow Air Conditioning Coil Cabinet

The furnace should be installed with coil cabinet part number specifi-
cally intended for downflow application. If a matching cooling coil is
used, it may be placed directly on the furnace outlet and sealed to pre-
vent leakage. For details of the coil cabinet dimensions and installation
requirements, refer to the installation instructions supplied with the coil
cabinet.

Attach the air conditioning coil cabinet to the duct connector, and then
position the furnace on top of the coil cabinet. The connection to the fur-
nace, air conditioning coil cabinet, duct connector, and supply air duct
must be sealed to prevent air leakage.

The cooling coil must be installed in the supply air duct, down-
stream of the furnace. Cooled air may not be passed over the heat
exchanger.

The minimum plenum height is 12” (30.5 cm). The furnace will not
operate properly on a shorter plenum height. The minimum recom-
mended rectangular duct height is 4 inches (10 cm) attached to the
plenum.

The duct system must be properly sized to obtain the correct airflow
for the furnace size that is being installed.
Refer to Table 6 or the furnace rating plate for the correct rise range
and static pressures.
If the ducts are undersized, the result will be high duct static pres-
sures and/or high temperature rises which can result in a heat
exchanger OVERHEATING CONDITION. This condition can result
in premature heat exchanger failure, which can result in personal
injury, property damage, or death.

 FIGURE 1:  

Duct Attachment

Factory
installed

For duct attachment,
if needed.

Summary of Contents for CM8M*MP

Page 1: ...Outside and Ambient Combustion Air 21 Gas Valve 25 Furnace Control Board 26 Wiring Diagram 30 LIST OF TABLES Unit Clearances to Combustibles 4 Coil Projection Dimensions PC Series Coils 8 Cabinet and...

Page 2: ...ting point provided that the tubes are lifted at the front of the heat exchangers where attached to the vestibule panel Do not use the top return bend of the heat exchangers as lifting points as the t...

Page 3: ...the National Fire Protection Association Inc Batterymarch Park Quincy MA 02269 or for only the NFGC contact the American Gas Association 400 N Capital N W Washington DC 20001 or www NFPA org CANADA NS...

Page 4: ...ng but not limited to decks and porches the following require ments shall be satisfied 1 INSTALLATION OF CARBON MONOXIDE DETECTORS At the time of installation of the side wall horizontal vented gas fu...

Page 5: ...es are rotated down for shipment In order to use the flanges remove the screw holding an individual flange rotate the flange so it is in the upward position and reinstall the screw then repeat this fo...

Page 6: ...igure 4 When moving or handling this furnace prior to installation always leave the doors on the furnace to provide support and to prevent damage or warping of the cabinet When lifting the furnace sup...

Page 7: ...te the vent blower 90 left or right so that the vent pipe passes through the side of the furnace casing rather than the end See Figure 6 COIL INSTALLATION COIL FURNACE ASSEMBLY MC FC PC SERIES COILS F...

Page 8: ...e furnace and coil casing and seal appropriately NOTE Dimension C should be at least 2 3 of dimension D See Fig ure 12 CRITICAL COIL PROJECTION The coil assembly must be located in the duct such that...

Page 9: ...24 25 29 5 For Cladded door add appoximately an additional 75 28 5 Electrical Entry Gas Pipe Entry Thermostat Wiring FRONT 14 1 1 5 23 SUPPLY END C 24 38 20 5 B Gas Pipe Entry Thermostat Wiring 33 A...

Page 10: ...as piping may be connected from either side of the furnace using any of the gas pipe entry on both sides of the furnace Refer to Figure 14 All filters and mounting provision must be field supplied All...

Page 11: ...he input rate back up to approxi mately 76 000 BTU H which is what it should be for that furnace at 6 000 feet SECTION V ELECTRICAL POWER ELECTRICAL POWER CONNECTIONS Field wiring to the unit must be...

Page 12: ...4 volt 40 VA transformer is sized for the furnace components only and should not be connected to power auxiliary devices such as humidifiers air cleaners etc The transformer may provide power for an a...

Page 13: ...tric heat on thermostat is not necessary C 24 Volt Common Y Compressor SINGLE STAGE AIR CONDITIONER Y Compressor Contactor SINGLE STAGE AIR CONDITIONER C 24 Volt Common R 24 Volt Hot Y1 Single Stage C...

Page 14: ...sed with batteries Thermostat Installer Setup 0170 System Type must be set to 8 2 Heat 2 Cool Multistage Conventional Connection of the C terminal 24 volt common is optional when used with batteries T...

Page 15: ...t Y1 Single Stage Compressor MODULATING FURNACE CONTROL G Fan MODULATING FURNACE Y Y2 Second or Full Stage Compressor DHUM Dehumidification Open on Humidity Rise W Modulating Heat Part Numbers SAP Leg...

Page 16: ...unction Light W Auxiliary Heat SINGLE STAGE HEAT PUMP 1 1 Part Number S1 2HU16700124 3 Y2 Second Stage Compressor Step 9 of Thermostat Installer Configuration Menu must be set to Pump OFF Step 1 of Th...

Page 17: ...2 OUT Second Stage Heat Y2 OUT Second Stage Compressor Y1 Single Stage Compressor X L Malfunction Light Y2 Second Stage Compressor W Auxiliary Heat BS Bonnet Sensor BSG Bonnet Sensor YORKGUARD VI CONT...

Page 18: ...at R 24 Volt Hot Heat XFMR RC 24 Volt Hot Cool XFMR AUX Auxiliary Heat Step 1 of Thermostat Installer Configuration Menu must be set to HP2 Selection of GAS ELEC switch on thermostat not necessary The...

Page 19: ...nal is removed 3 Hot Heat Pump The hot heat pump feature will work when the control is wired to a 2 stage thermostat and a 2 stage heat pump 4 Hot Heat Pump The hot heat pump feature will not work whe...

Page 20: ...have no dimen sion smaller than 0 25 0 64 cm 3 A manually operated damper or manually adjustable louvers are not permitted for use 4 A automatically operated damper or automatically adjustable lou ve...

Page 21: ...ional area as the free area of the air supply inlet opening to which it connects 4 The blocking effects of louvers grilles and screens must be given consideration in calculating free area If the free...

Page 22: ...ollowing steps shall be followed for each appliance connected to the venting system being placed into operation while all other appliances connected to the venting system are not in operation 1 Inspec...

Page 23: ...per input rate using natu ral gas with a heating value of 1030 BTU Ft3 38 4 MJ m3 If the heat ing value of your gas is significantly different it may be necessary to replace the orifices NOTE DO NOT s...

Page 24: ...300 750 78 46 92 231 25 144 288 720 80 45 90 225 26 138 277 692 82 44 88 220 27 133 267 667 84 43 86 214 28 129 257 643 86 42 84 209 29 124 248 621 88 41 82 205 30 120 240 600 90 40 80 200 31 116 232...

Page 25: ...urnace temperature rise Take temperature readings of both the return air and the heated air in the ducts about six feet away from the furnace where they will not be affected by radiant heat Increase o...

Page 26: ...removed Electrical supply to this unit is dependent upon the panel that covers the blower compartment being in place and properly positioned ROLLOUT SWITCH CONTROLS These controls are mounted on the...

Page 27: ...l senses that flame is present the circulating blower starts at low speed 5 The furnace fires at 70 of full rate for 30 45 seconds then drops to the minimum 50 firing rate 6 The firing rate is automat...

Page 28: ...not connected properly check for loose plug or loose wires in plug Steady On Red Control fault has been detected or there is 24 volts present without 115 volts Check that there is 24 volts and 115 vol...

Page 29: ...L Models Only MISCELLANEOUS ORIFICE BURNER Natural 45 SIGHT GLASS OVAL 2 Req d GASKET FOAM Door 1 5 ft req d GASKET INTAKE PAN PLUG VENT HOLE BRACKET DOOR WIRING HARNESS FERRULE 3 Req d GROMMET 3 Req...

Page 30: ...nted in U S A 368261 UIM B 1008 Copyright 2008 by Johnson Controls Inc All rights reserved Supersedes 368261 UIM A 0508 Johnson Controls Unitary Products 5005 York Drive Norman OK 73069 SECTION XI WIR...

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