4
SUPPLY DUCTING AND REGISTERS
A.
Ducting
1.
The field fabricated supply ducting must attach to
both sides of the ceiling plenum. A minimum of two
ducts are required, with one duct attached to each
side of the plenum (See Figure 1).
2.
Each duct must have a minimum height of 1 1/2",
maximum height cannot exceed 4 inches. Total free
area inside each duct must be no less than 10 square
inches.
NOTE
To decrease restriction and increase air flow, the
ducting should make as few bends and turns as
possible. When corners or turns are required, we
recommend that you radius the corners to keep air
flow at a maximum.
Ten (10) square inches of free area per duct is the
minimum requirement, larger ducting will improve
air flow and system performance.
3.
Where ducting secures to the ceiling plenum,
maximum width is 8 inches.
4.
All field fabricated cold air supply ducting must be
insulated and must have a vapor barrier.
IMPORTANT
Insulation reduces cooling loss and helps prevent
water staining of the vehicle ceiling due to
moisture condensation.
B.
Registers
Supply (cold air) registers should have a minimum
discharge area of 48 square inches per system, or 24
square inches per duct. A minimum of 6 is
recommended.
Plenum
Terminal
Designation
Thermostat
Wire
Connection
Function Of Low Voltage Terminal
Extending From Ceiling Plenum
B
BLUE
Completes -12 VDC circuit for all relays
Y
YELLOW
Energizes coil on Compressor Relay
GH
GREEN
Energizes coil on High Fan Relay
GL
GRAY
Energizes coil on Low Fan Relay
W
WHITE
Energizes coil on Heat Relay
“Heat Ready”
Boxes
“Cool Only”
Boxes
FREEZE
FREEZE
WHITE
Evaporator Freeze Sensor Connections
