Operator's Manual: Models CB-3500 & CB-5000
7-4
The Auxiliary Hi-Temp Limit Switch
The CB-3500 and CB-5000 furnaces are equipped with an auxiliary L-290 high temperature limit switch which
is mounted on a bracket at the front of the combustion chamber as shown in Figure 7B. This switch senses the
build-up of heat within the combustion chamber beyond the fan limit control setting and is designed to protect the
furnace from damage due to overheating.
Understanding the Function of the Auxiliary L-290 Auto-Reset Hi-Temp Limit Switch
If the temperature of the combustion chamber has exceeded the range of the fan limit control, the auxiliary
L-290 auto-reset hi-temp limit switch opens and shuts off power to the primary control on the burner, and the
burner shuts down. After the combustion chamber has sufficiently cooled, the L-290 switch will
automatically
reset, and allow the burner to re-start.
The L-290 hi-temp limit switch will open and shut down the burner if any of the following conditions exists:
•
If the fan/blower has stopped running for any reason during furnace operation,
the heat
in the furnace may cause the L-290 hi-temp limit switch to open. Ensure that the fan/blower is
functioning properly.
•
The fan limit control is not functioning properly.
If the fan limit control has malfunctioned,
the L-290 could cycle on/off repeatedly. If this occurs, contact your Clean Burn Distributor
immediately for service.
•
The furnace is overfiring.
Review the directions in Section 6 in the Operator’s Manual 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 of the Operator’s
Manual.
ATTENTION:
It is very important to determine the reason for the opening of the L-290 switch 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.
Summary of Contents for CB-3500 series
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