Ford F-650 2015 Owner's Manual page 204

Periodically inspect parts such as air brake chamber diaphragm, air
compressor and air cleaner. Replace any parts if you can consider them
unserviceable.
Air dryer: Climactic conditions affect performance of desiccant or
after-cooler type air dryers. You must establish a maintenance schedule
for each specific operation.
The use of an air dryer on a vehicle does not eliminate the need to drain
the air reservoirs periodically.
Desiccant air dryer: Inspect for moisture in the air system by opening
reservoirs, draincocks or valves and checking for presence of water. The
presence of small amounts of water due to condensation is normal and is
not an indication that the dryer is not functioning properly.
Replace or rebuild the desiccant cartridge when you determine that the
desiccant is contaminated and does not have adequate water absorption
capacity. The desiccant change interval may vary. A general
recommendation is to replace the desiccant every 12 months (yearly). If
experience has shown that extended or shortened life has resulted for a
particular installation, then the yearly interval can be increased or
decreased accordingly.
system. Contact an authorized dealer if you are unsure of the air
reservoir locations or the draining procedure.
WARNING: Failure to drain air brake reservoirs can result in a
reduction or loss of braking ability due to fluid accumulation in
the reservoir and/or possible freeze-up during cold weather.
2015 F-650/750 (f67)
Owners Guide gf, 2nd Printing, April 2014
USA (fus)
Maintenance
Draining the air brake reservoir:
Completely drain all the air brake
reservoirs daily by opening the
draincock at the ends of the tanks.
(Where accessible. Pull-chains are
used when the drains are undercab
or otherwise inaccessible.) Close the
draincock after draining. Manually
drain any air tanks equipped with
automatic moisture ejector valves,
as required, to maintain a dry air
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