American Standard 300A - Manual (Page 10)

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VI. PERIODIC PREVENTIVE MAINTENANCE
NOTE: Periodic inspection and preventive maintenance of your total
heating system is important for efficient and safe operation. Your heating
dealer should perform humidifier service at the same time.
All models are equipped with an in-line water strainer and orifice as
shown below. These parts should be inspected and cleaned periodically to
assure continued proper unit performance.
1. Disconnect electrical power to the furnace
and shut off water supply.
2. Disconnect the water line at the inlet
compression nut.
3. Remove the in-line strainer from inside the
inlet fitting by using a small nail or wire.
4. Flush the in-line strainer clean or replace
with a new strainer, Service Part No.
SRA00859.
5. Replace the in-line strainer and reconnect
the inlet water line.
(Double Wrench To Prevent Leaking.)
6. Disconnect the water line at the outlet
compression nut.
7. Remove the orifice from the copper or plastic tube and make sure this
small opening is unplugged.
8. Replace the orifice and reconnect the outlet water line.
(Double Wrench To Prevent Leaking.)
9. Turn on water supply @ Saddle Valve and reconnect electrical power to
the furnace.
INSPECTION AND SERVICE INSTRUCTIONS