Carrier 48DH - Manual (Page 9)

GENERAL OPERATING SEQUENCES
These sequences apply to both natural and LP
gas units in normal operation after initial start-up.
Operating Sequence — Heating
1. Pilot ignited. Thermostat selector switch at
“Heat” or “Auto.” Thermostat dial set above
room temperature.
2. Main gas valve circuit is energized. Gas valve on
LP units opens immediately; gas valve on
natural gas units opens in 10 — 15 seconds.
3. TDR starts indoor fan in 30 — 45 seconds.
4. When thermostat setting is satisfied, main gas
circuit de-energizes. LP gas valve closes imme­
diately; natural gas valve closes in 1 0 — 1 5
seconds. Gas flow to main burners stops and
flame is extinguished.
5. TDR stops indoor fan 1.0 — 1.5 minutes after
thermostat setting is satisfied.
6. Limit switch shuts off gas valve if air circulation
is restricted, but fan continues to run. Pilot
automatically reignites if extinguished.
Operating Sequence — Cooling
1. Unit energized. Thermostat selector switch at
“Cool” or “Auto.” Thermostat dial set below
room temperature.
2. Indoor and outdoor fans and compressor start.
3. When thermostat setting is satisfied, fans and
compressor stop.
Automatic Operation — Power and gas on. Room
thermostat (control center) set at “Auto.” Fan
switch (on control center) set at “Auto.”
Unit performs as described in the operating
sequences above on call for heating or cooling.
Automatic changeover type thermostat is required.
Continuous Fan Operation — With power supplied
to unit and fan switch at “On” position, indoor fan
remains on at all times.
Size 002 units require a field-installed accessory
indoor fan relay with N.O. contacts in parallel with
TDR contacts for continuous fan operation.
Complete Shutdown or Change from Heating to
Cooling
1. Turn thermostat selector switch to “Off.”
Table 5 — Manifold
2. Remove heating section access panel.
3. Turn manual shutoff valve (Fig. 8) to “Pilot.”
Then depress valve and turn to “Off.”
4. Turn off power. Replace access panel.
SERVICE
Adjusting Main Burner Gas Input
(Refer to Fig. 4 and 8 and to Table 5 and 6) —
Need for adjustment is determined by comparing
measured gas input (flow rate or manifold
pressure) against the rated input of a gas with a
specific heating value. Check local gas supplier for
correct heating value (BTU’s per cu ft). Before
measuring, shut down all other gas appliances.
Flow rate (cfm), the most accurate method, is
measured by gas meter and stop watch. Check
measured flow against rated flow in Table 6.
Manifold pressure (in. wg) is measured as
follows:
1. Remove heating section access panel.
2. Shut down unit and close gas supply line valve
(Fig. 4).
3. Remove pressure tap plug from main gas valve
(Fig. 8) and install pressure tap.
4. Attach U-tube water gage manometer to
pressure tap and open gas supply line valve.
5. Start up heating system.
6. Measure gas pressure (in. wg) and compare with
rated pressure in Table 5.
To adjust pressure or flow rate:
1. Remove pressure regulator adjusting screw cap
on main gas valve (Fig. 8).
2. Turn screw slowly, clockwise to increase pres­
sure (flow), and counterclockwise to decrease.
3. Replace adjusting screw cap.
4. Shut down heating system.
5. Close gas supply line valve, remove manometer
and replace pressure tap plug.
6. Open gas supply line valve and replace heating
section access panel.
Pressure {in. wg)
TYPE BTU
SP
GR
UNIT
MAIN
PILOT
ORIFICE
OF PER 48DH 48DM 48DL BURNER
GAS CU FT 002 004 005 004 002 003 004 045 005 ORIFICE
1000
,60 3.3 3,0 3.0 3,4 3.5 3.3 3.3 3.0 3.4
65 3.5 3.2 3.2 3.6 3 7 3 5 3.5 3.2 3.6
Natu ra! 1050
.60 3.0 2.7 2.7 3.1 3.2 3.0 3.0 2.7 3,1 J #41
016 in
Drill 65 3.2 2.9 2.9 3,3 3.4 3 2 3.2 2.9 3.3 1
1100
.60 2.7 2.4 2.4 2.8 2.9 2.7 2.7 2.4 2.8
.65 2.9 2.6 2.6 3.0 3.1 2.9 2.9 2.6 3.0
Butane 3200 2 00 11 5 10 5 10 5 12 2 12 0 11 5 11.5 10 5 12 2 #54
010 in
Propone 2500 1.53 12 2 11 2 11 2 12 9 13 0 )2 2 12 2 11 2 12 9 Drill
SP GR — Specific Gravity