Carrier SINGLE PACKAGE ROOFTOP UNITS ELECTRIC COOLING/GAS HEATING 48HJ015-025 - Manual (Page 17)

Table 7 — Accessory/FIOP Economizer Static Pressure (in. wg)
UNIT
480HJ
UNIT
VOLTAGE
CFM
ECONOMIZER
PRESSURE DROP
015, 017 All
3,750 .03
4,000 .03
5,000 .05
6,000 .07
7,500 .10
025 All
6,000 .07
7,200 .09
9,000 .11
10,000 .12
LEGEND
BHP — Brake Horsepower
FIOP — Factory-Installed Option
NOTES:
1. The factory-assembled horizontal adapter substantially improves
fan performance. See Fig. 24.
2. The static pressure must be added to external static pressure. The
sum and the evaporator entering-air cfm should then be used in
conjunction with the Fan Performance table to determine blower
rpm, bhp, and watts.
Gas Heat — Verify gas pressures before turning on heat
as follows:
1. Turn off manual gas stop.
2. Connect pressure gage to supply gas tap (See Fig. 13 on
page 8).
3. Connect pressure gage to manifold pressure tap on gas
valve.
4. Turn on manual gas stop and set thermostat to HEAT po-
sition. After the unit has run for several minutes, verify
that incoming pressure is 5.0 in. wg or greater, and that
the manifold pressure is 3.5 in. wg. If manifold pressure
must be adjusted, refer to Gas Valve Adjustment section
on page 22.
5. After unit has been in operation for 5 minutes, check tem-
perature rise across the heat exchangers. See unit infor-
mative plate for correct rise limits of the heat supplied.
Air quantities may need to be adjusted to bring the actual
rise to within the allowable limits.
Base Unit Operation
COOLING, UNITS WITHOUT ECONOMIZER — When
thermostat calls for cooling, terminals G and Y1 are ener-
gized. The indoor (evaporator) fan contactor (IFC) and
compressor contactor no. 1 (C1) are energized and evaporator-
fan motor (IFM), compressor no. 1 (017,025) or unloaded
compressor (015), and condenser fan start. The condenser-
fan motors run continuously while unit is cooling. If the ther-
mostat calls for a second stage of cooling by energizing Y2,
compressor contactor no. 2 (C2) is energized and compres-
sor no. 2 starts (017,025), or compressor no. 1 runs fully
loaded (015).
A freeze protection thermostat (FPT) is located on the
evaporator coil. It detects frost build-up and locks out the
compressors, allowing the coil to clear. Once frost has melted,
the compressors can be reenergized by resetting the
thermostat.
HEATING, UNITS WITHOUT ECONOMIZER
NOTE: The 48HJD015 units have 1 stage of heat, and the
48HJE015, 48HJE017, and HJD025 units have 2 stages of
heat.
First Stage — Turn unit power on. Open manual gas line
valve. Set thermostat system switch at HEAT or AUTO. po-
sition and set fan switch to AUTO. position for heating.
First-stage thermostat calls for heat. Time-delay relay for
evaporator fan begins timer sequence. Induced-draft relay
closes, and induced-draft motor starts.
Pressure switch closes and pilot valve no. 1 opens, allow-
ing gas to flow to the first-stage pilot. Spark ignitor
ignites pilot flame. Sensor detects flame and the main gas
valve no. 1 opens. Gas flows to main burners and first-stage
burners ignite. Spark igniter turns off.
When sequence is complete, time-delay relay closes and
evaporator fans start.
Second-Stage — On 2-stage units, with an additional heat-
ing call, the second-stage thermostat closes. (The control re-
lay [HR2] closes during the first stage of operation.) Pilot
valve no. 2 opens, and the spark ignitor ignites pilot. The
sensor detects a flame and energizes main gas valve coil
no. 2, opening main gas valve no. 2. Gas flows to the main
burners, and the second-stage burners ignite. The spark ignitor
turns off.
When the second-stage thermostat is satisfied, the second-
stage gas valve closes.
When the first-stage thermostat is satisfied, the first-stage
gas valve closes. The induced-draft motor turns off, the time
delay relay is deenergized, and the timer sequence begins.
When the sequence is complete, the evaporator-fan motor
turns off.
COOLING, UNITS WITH ECONOMIZER — Upon a call
for cooling, when outdoor ambient is above the changeover
control setting, the economizer damper moves to VENT
position. The compressors and evaporator and condenser fans
energize and operate as per Cooling, Units Without Econo-
mizer section above.
Upon a first call for cooling, when outdoor ambient is be-
low the changeover control setting, the evaporator fan starts
and the economizer is fully open. The compressors remain
off.
Upon a second-stage call for cooling, compressor no. 1
(017,025) or unloaded compressor (015) is energized and me-
chanical cooling is integrated with economizer cooling. If
the outdoor-air temperature drops below 50 F, a cooling lock-
out switch prevents the compressors from running.
When supply-air temperature drops below a fixed set point,
the economizer damper modulates to maintain the tempera-
ture at the fixed set point.
HEATING, UNITS WITH ECONOMIZER — Outdoor-air
damper stays at VENT position while evaporator fan is
operating.
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