CLEAN BURN CB 140, Operator'S Manual

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Operator's Manual: Models CB-1750, CB-2500 & CB-3250
7-2
The Blower Switch
The CB-1750/2500/3250 furnaces feature an F-180 blower/fan switch (normally open) which is surface
mounted at the front of the combustion chamber (see Figure 7B). The blower/fan switch senses the
temperature of the combustion chamber as the burner is firing. When the combustion chamber reaches
the proper temperature, the blower/fan switch closes and sends power to the blower motor (CB-1750)
or relay (CB-2500/3250) to turn ON the blower motor. When the wall thermostat is satisfied and the
burner shuts off, the blower continues to run until the switch senses that the combustion chamber has
cooled down. The switch then opens and shuts off the blower motor.
The Hi-Temp Limit Switches
These furnaces also feature two high temperature limit switches which are mounted on a bracket at the front of
the combustion chamber as shown in Figure 7B. The switches sense the build-up of heat within the combustion
chamber and are designed to protect the furnace from damage due to overheating. The limit switches are wired in
series, and both are auto-resetting.
Understanding the Function of the L-200 Hi-Temp Limit Switch
If the temperature of the combustion chamber is too hot, the L-200 hi-temp limit switch opens and shuts off power
to the primary control on the burner, and the burner shuts off. The blower continues to run to cool down the
furnace. After the combustion chamber has cooled down, the L-200 hi-temp limit switch will automatically reset
and allow the burner to restart.
ATTENTION: If the L-200 hi-temp limit switch is opening repeatedly, the burner MUST be readjusted
according to the instructions in Section 6 to correct the overheating problem, or serious damage to the furnace
may occur.
The L-200 hi-temp limit switch will open and shut down the burner if any of the following conditions exists:
•
The furnace is over firing.
Review the directions in Section 6 to properly adjust the burner.
•
Improper ductwork is installed on the furnace (applicable only if your furnace is
operating as a central furnace). Ductwork must be installed by qualified HVAC personnel
according to industry standards and the specifications provided in Section 3.
Understanding the Function of the L-290 Auxiliary Auto-Reset Hi-Temp Limit Switch
The L-290 auxiliary auto-reset high temperature limit switch is a back-up safety switch for the L-200 hi-temp
limit switch.
Both the L-200 and L-290 auxiliary hi-temp limit switches will open and shut down the burner if:
•
the blower has stopped running for any reason during furnace operation,
the heat
in the furnace will cause the limit switches to open. Ensure that the blower is functioning properly.
ATTENTION: It is very important to determine the reason for the opening of the limit switches and take steps
to correct the cause; failure to do so may result in serious overheating and damage to the heat exchanger of the
furnace. Additionally, if the burner is rapidly cycling on/off, contact your Clean Burn Distributor immediately;
failure to address this situation may result in serious damage to the furnace.