Carrier 58DR - Manual (Page 7)

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, limit 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, blower motor MTR
continues to operate because heat relay HFR is deenergized
to cool down the furnace.
Manual reset auxiliary limit switch ALS is located on the
top right-hand comer of the furnace. In the event of blower
motor failure, this switch breeiks the electrical circuit to the
gas valve, stopping gas flow to the main burners. The
switch must be manually 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 Emd 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 completely blocked vent condition occurs.
During a blocked vent condition, temperature in the
drafthood relief opening wfll rise causing vent safety shut­
off switch to open, breaking the circuit to gas valye GV. The
gas valve closes immediately, stopping gas flow to the main
burners and pilot, and the blower wfll run continuously.
The furnace wiU 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 supplied 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 deunper 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
remain open until the thermostat is satisfied.
When the thermostat is satisfied, it wfll deenergize the main
gas valve and stop the gas flow. The vent damper motor wfll
energize and close the damper. When the vent damper
reaches the full-closed position, the damper motor is
deenergized and will remain so until the next “call for heat”
by the thermostat.
C. Cooling (Cooling Models Only)
When the thermostat “calls for cooling,” power from trans­
former TRAN energizes the condensing unit contactor, cool­
ing relay coil CFR, closing its contacts and energizing
blower motor MTR on its cooling speed. It continues to
operate until the thermostat is satisfied.
When the thermostat is satisfied, the circuit to terminal Gc
is broken, deenergizing cooling relay coil CFR which, in
turn, opens its contacts, stopping blower motor MTR.
VIII. FILTER ARRANGEMENT
The two factory-supplied filters are shipped in the blower
compartment. After the return-air duct has been connected
to the furnace, install the filters hi a V-formation inside the
return-air plenum. See Fig. 11.
A WARNING
Never operate the unit without a filter or with the filter
access door removed. A failure to adhere to this warn­
ing can cause a fire, physical injury, or death.
,-INSTALLATION
POSITION
OF FILTERS
A78654
Fig. 11—Position of Fiiters
IX. STARTUP AND ADJUSTMENT
In addition to the following information, refer to “Proce­
dures for Natural-Draft Gas-Fired Furnaces” packaged with
the unit.
NOTE: There is a switch located in the blower compartment
that breaks the electrical power supply when the blower
access door is removed. Be sure the blower access door is
properly installed.
A CAUTION
This furnace is equipped with a fusible link in the vesti­
bule area that wfll melt if an overheating condition
caused by an inadequate combustion-Eur supply or
improper venting practices develops.
Do not jumper
this fuse. Correct the condition and replace the fuse
with an identical part.
The gas service pressure must not exceed 0.5 psig (14
in. wc).
NOTE: The gas valve regulator has been nominally-set at
3.5 in. wc for natural gas. Refer to “Procedures for Natural-
Draft Gas Furnace Installation” for readjusting when
checking input.
A. Adjustment of Blower Speed
A WARNING
Disconnect the electrical power before changing the
speed tap. A failure to adhere to this warning can cause
personal injury.