General System Operation - Field Controls CAS-34U Manual

GENERAL SYSTEM OPERATION

1. The thermostat (wall thermostat or aquastat) calls for heat which activates the CAS-34U unit. After the
CAS-34U fan has come up to speed and air fl ow into the CAS-34U inlet is established, an internal air
pressure switch closes and completes the circuit to allow the burner to fi re. If the appliance is power
vented, the venter and CAS-34U activate simultaneously. After the CAS-34U and power venter have come
up to speed, a pressure switch in the power venter control also closes and allows the appliance to fi re.
2. After the heating requirement has been satisfi ed, the thermostat circuit will open and deactivate the
burner and CAS-34U unit.
3. For power vented systems with a post purge device, the power venter and CAS-34U operate for a period
of time after the burner has shut off to purge remaining fl ue gases from the vent system.
This device must be installed by a qualifi ed installer in accordance with the manufacturer's installation instructions.
SIZING AND SETUP
Table 1 shows the maximum equivalent length and size of duct pipe that should be used when installing the
CAS-34U system. Using this table will help ensure that the proper amount of air is drawn into the structure as
needed by the appliance. Follow the guidelines below to properly size and set up the CAS-34U.
1. Determine the maximum input fi ring rate of the appliance, or the maximum total fi ring rate of multiple
appliances that will be used.
2. Position the motorized CAS-34U unit according to the guidelines in the "Installation" section.
3. Determine where the intake air hood will be located based on the recommendations in the "Installation"
section.
4. The CAS-34U is equipped with a High/Low motor speed control switch. When calculating the maximum
equivalent feet, determine which speed is appropriate for the application. (Refer to Tables 1 and 2)
5. Calculate the total equivalent length of duct pipe including elbows and fi ttings needed to connect the
CAS-34U unit to the intake air hood. (Refer to Table 1)
6. On Table 1, locate the point that corresponds to the correct combination of fi ring rate and duct size.
CAUTION
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P/N 780107600 Rev B 05/23