52
•
Circulator blower is energized on the appropriate cool speed at the level and time determined by the selected ramping profile.
Electronic air cleaner terminal is energized with circulator blower.
•
Furnace circulator blower and outdoor cooling unit run their appropriate speeds, integrated control module monitors safety
circuits continuously.
•
R and Y1/G or Y2/G thermostat contacts open, completing the call for cool.
•
Outdoor fan and compressor are de-energized.
•
Circulator blower continues running during a cool off delay period. The OFF delay time and airflow level are determined by the
selected ramping profile.
• Electronic air cleaner terminal and circulator blower are de-energized.
•
Furnace awaits next call from thermostat.
F
AN
O
NLY
M
ODE
The normal operational sequence in fan only mode is as follows:
•
R and G thermostat contacts close, initiating a call for fan.
•
Integrated control module performs safety circuit checks.
•
Circulator blower is energized on continuous fan speed (25%, 50%, 75% or 100% DIP switch selectable when using a
conventional thermostat). Electronic air cleaner terminal is energized.
•
The furnace control board HUM dry contacts close.
•
Circulator blower runs, integrated control module monitors safety circuits continuously.
•
R and G thermostat contacts open, completing the call for fan.
•
Circulator blower is de-energized. Electronic air cleaner terminal is de-energized.
•
Furnace awaits next call from thermostat.
O
PERATIONAL
C
HECKS
The burner flames should be inspected with the burner compartment door installed.
Flames should be stable, quiet, soft, and blue (dust may cause orange tips but they must
not be yellow). Flames should extend directly outward from the burners without curling,
floating, or lifting off. Flames must not impinge on the sides of the heat exchanger
firing tubes.
S
AFETY
C
IRCUIT
D
ESCRIPTION
A number of safety circuits are employed to ensure safe and proper furnace operation.
These circuits serve to control any potential safety hazards and serve as inputs in the
monitoring and diagnosis of abnormal function. These circuits are continuously monitored during furnace operation by the integrated
control module.
F
URNACE
C
ONTROL
B
OARD
The furnace control board is an electronic device which, if a potential safety concern is detected, will take the necessary precautions
and provide diagnostic information through an LED display.
P
RIMARY
L
IMIT
The primary limit control is located on the partition panel and monitors heat exchanger compartment temperatures. It is a normally-
closed (electrically), automatic reset, temperature-activated sensor. The limit guards against overheating as a result of insufficient
conditioned air passing over the heat exchanger.
A
UXILIARY
L
IMIT
The auxiliary limit controls are located on or near the circulator blower and monitors blower compartment temperatures. They are a
normally-closed (electrically), auto-reset sensors. These limits guard against overheating as a result of insufficient conditioned air
passing over the heat exchanger.
Check the
Burner Flames for:
1. Stable, soft and blue.
2. Not curling, floating
or lifting off.
Burner Flame
Figure 53
