Separated Combustion Indoor Gas Fired Make-Up Air Units - High Limit and/or Safety Limit Maintenance

High Limit and/or Safety Limit Maintenance

• Turn off the manual gas valve and electrical power to the MS unit

• To access the high limits, remove the four screws from the top of the raceway on each furnace section and swing the raceway down. The primary limit can be removed by removing the two screws holding the high limit bracket to the heat exchanger and removing the bracket and limit assembly from the heat exchanger.

• Note location of and remove wires from limit switch, then remove push nuts and springs holding limit switch to bracket. Re-assemble in reverse order making sure that parts are assembled so that spring pressure holds limit switch securely against bottom header plate of heat exchanger.

• To remove the secondary high limit, remove the wires from the limit switch, remove the screws and stand-off sleeves holding the limit switch body to the mounting plate. Do not remove the screws holding the mounting plate to the heat exchanger.

• Slowly pull the switch and capillary assembly out of the retaining tube, taking care to prevent kinking the capillary tube. Re-assemble in reverse order, carefully pushing the capillary tube into the retaining tube to prevent kinking the capillary tube.

• Complete appropriate start-up procedure as given in the “Start-Up” section of the manual.

• Check Burner Adjustment.

• Check gas control valves and pipe connection for leaks.

• Check operation of auto gas valve

• Check operation of safety devices.

• Inspect and service blower section of system.