Carrier 58DP - Manual (Page 7)

IMPORTANT:
The thermostat heat anticipation must be set
to match the amp draw of the gas valve and electrical com­
ponents in the R-W circuit. Accurate amp draw readings
can be obtained at thermostat subbase terminals R & W.
Fig. 7 illustrates an easy method for obtaining the actual
amp draw.
The room thermostat should be located where it wiU be in
the natural circulation path of room air. Avoid locations
where the thermostat would be exposed to cold-air infiltra­
tion, drafts from windows, doors, or other openings leading
to the outside, or exposure to air currents from warm- or
cold-air registers; or to exposure where the natural circula­
tion of the air is cut off—such as behind doors, above or
below mantels, shelves, etc.
The thermostat should not be exposed to heat from nearby
fireplaces, radios, televisions, lamps, or rays from the sun.
Nor should the thermostat be mounted on a wall containing
pipes or warm-air ducts, or a flue or vent that could affect
its operation and prevent it from properly controlling the
room temperature. Any hole in the plaster or panel through
which the wires pass from the thermostat should be ade­
quately sealed with suitable material to prevent drafts from
affecting the therniostat.
C. Blower Control Center
Each furnace features a printed-circuit control center. This
will aid the installer and serviceman when installing and
servicing the unit. See Fig. 8. A low-voltage terminal board
is marked for easy connection of field wiring.
VII. SEQUENCE OF OPERATION
NOTE:
The wiring diagrams shown in Figs. 10 and 11 cover
heating/coohng units.
A. Heating
Gas and electrical supplies must be turned on at the
furnace.
NOTE:
When power is apphed to heat relay cofl. HFR in the
control circuit, the normally closed contacts in the blower
circuit will open.
1. White Rodgers 36E Gas Valve piD Models). See Fig. 10.
When the thermostat “calls for heat,” the control circuit is
closed between terminals R and W. Power from transformer
TRAN through fusible link FL, hmit switches LS & ALS
and vent safety shut-off switch VSSS, energizes the pilot
valve part of automatic gas valve GV and pilot igniter PI.
The pilot valve opens, permitting gas flow to the pilot
burner where it is ignited.
The pilot valve portion of automatic gas valve GV has a
“pick” solenoid coil and latching “hold” device. The “pick”
coU must be energized to open the pilot valve, but only the
“hold” device must be energized to keep it open.
The “hold” device varies with the gas valve design used on
the furnace. It could be an internal pressure switch in series
with the “pick” solenoid coil, an raternsil electrical resistor
in series with the solenoid “pick” coil, or a separate electri-
ceil solenoid coU.
When the pilot flame is estabhshed, safety pilot SP switches
its contacts in approximately 40 to 60 seconds, energizing
the main valve portion of gas valve GV and deenergizing
safety pilot igniter SP and the “pick” coil of the pilot sole­
noid portion in gas valve GV. The pilot valve is held open by
the “hold” device within gas valve GV.
The main valve portion of gas valve GV has a delayed open­
ing operator that opens within 6 to 15 seconds after it is
energized, permitting gas flow to the main burners where
the gas is ignited by pilot SP.
2. Honeywell VR 800A Gas Valve (Match-Lit Models). See
Fig. 11
The furnace pilot must be ht to energize the thermal magnet
circuit of gas valve GV, thus permitting gas flow to the
remaining portion of the valve.
When the thermostat “calls for heat,” the control circuit is
closed between terminals R and W. Power from transformer
TRAN through fusible linkn FL, limit switch LS & ALS and
vent safety shutoff switch VSSS energizes gas valve GV,
causing the valve to open and permitting gas flow to the
main burners, where it is ignited by the pilot.
3. Blower Circuit
With power through the solid-state time-delay circuit on
printed-circuit board PCB and heat relay HFR, blower
motor MTR is energized on heating speed approximately 75
seconds after gas valve GV has been energized (or the pilot
flame has been proven in the case of IID systems).
4. Limit Control
If the furnace overheats for any reason, hmit control LS
switches, breaking the circuit to automatic gas valve GV.
The gas valve closes immediately, stopping gas flow to the
main burners and the pilot. In addition, Iplower motor MTR
continues to operate because heat relay HFR is deenergized
to cool down the furnace.
Manual reset auxffiary limit switch ALS is located on the
top right-hand corner of the furnace. In the event of blower
motor failure, this switch breaks the electrical circuit to the
gas valve, stopping gas flow to the main burners. The
switch must be manuahy reset after the blower motor has
been replace.
Fusible link FL is provided in the transformer TRAN sec­
ondary circuit as protection from overheating conditions in
the vestibule area of the furnace. Should this condition
exist, the fuse opens and deenergizes gas valve GV and heat
relay HFR, stopping the gas flow to the burners and start­
ing blower motor MTR.
When the thermostat is satisfied, the circuit between R and
W is broken, deenergizing automatic gas valve GV, pilot SP
(when used), and the solid-state time-delay circuit on
printed-circuit board. The gas flow stops immediately to the
pilot and main burners with the IID controls, and to the
main burners only with standing pilot controls. After
approximately 105 seconds, heat relay HFR is energized
and blower motor MTR stops.
5. Vent Safety Shut-off System Switch
The purpose of this control is to safely shutdown the fur­
nace if a blocked vent condition occurs.
During a blocked vent condition, temperature in the
drafthood opening will rise causing vent safety shut-off
switch to open, breaking the circuit to gas valve GV. The
gas valve closes immediately, stopping gas flow to the main
burners and pilot, and the blower will run continuously.
The furnace will remain in this mode until the vent safety
shut-off system switch is manually reset.
B. Vent Damper (When Used)
With gas and electrical power supphed to the furnace, the
vent damper motor is deenergized, and the vent damper is
closed until the thermostat “calls for heat.”
On a “call for heat” by the thermostat, the vent damper
motor is energized and the damper opens. When the vent
damper reaches the full-open position, the damper motor is
deenergized and a circuit is completed to the main gas valve
via the pilot. At this time, the main gas valve is energized
and the main burners are ignited; the vent damper will
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