Check Safety Controls; Checklist - Carrier 58EFB Installation, Start-Up, And Operating Instructions Manual

Step 6—Check Safety Controls
CHECK PRIMARY LIMIT CONTROL
The heat sensing switch performs as the furnace high temperature
limit switch. If furnace overheats for any reason, the limit switch
opens, breaking circuit to main gas valve. If limit is activated
check for a restriction in duct system (dirty filters, blocked duct
work, closed registers, etc.). The blower motor is energized and as
unit cools, limit switch closes. This relights main burners, but
unless overheating condition is corrected, furnace will cycle on
limit. Corrective action must be taken.
The recommended method of checking limit control is to gradually
block off return air after furnace has been operating for a period of
at least 5 minutes. As soon as limit control has shut off burners,
return-air opening should be unblocked to permit normal air
circulation. By using this method to check limit control, it can be
established that limit is functioning properly and will operate if
there is a restricted circulating air supply or motor failure. If limit
control does not function during this test, the cause must be
determined and corrected.
CHECK PRESSURE SWITCH (BLOCKED-VENT SHUTOFF
SWITCH)
This control proves operation of the draft inducer. Check switch
operation as follows:
1. Turn off 115-v power to furnace.
2. Remove control box cover and disconnect inducer motor lead
wires from control board.
3. Turn on 115-v power to furnace.
4. Set thermostat to call for heat. When pressure switch is
functioning properly, ignitor should not glow. If ignitor glows
when inducer motor is disconnected, shut down furnace
immediately. Determine the reason pressure switch did not
function properly and correct the condition.
5. Turn off 115-v power to furnace.
6. Reconnect inducer motor lead, reinstall control box cover, and
turn on 115-v power supply.
FLAME ROLLOUT SWITCH
This furnace is equipped with a manual reset flame rollout shutoff
switch which is attached to burner/manifold assembly. In the event
that a blockage prevents venting of flue gases from heat exchanger,
the switch detects conditions that would produce a flame rollout
and shuts off power to automatic gas valve before there is furnace
damage or a flame rollout outside of furnace cabinet. The loss of
power to gas valve shuts off gas burners, however, blower is still
controlled by fan and limit switch and operates until heat ex-
changer temperatures have cooled.
1. Put away tools and instruments. Clean up debris. Verify that
blower and control access panels are properly installed.
2. Cycle test furnace with room thermostat.
3. Check operation of accessories per manufacturer's instruc-
tions.
4. Review User's Guide with owner.
5. Leave literature packet near furnace.
18

CHECKLIST