GMC T-Series 1999 Owner's Manual page 227

Air Dryer (Option)
If your vehicle has air brakes, it may have an air dryer.
This collects and removes dirt, moisture or other foreign
matter from the air prior to entering the brake system. It
is mounted on the left frame rail.
If your dryer is a
-
Bendix Westinghouse, it
has a filter that you need to
change at intervals. See
your Maintenance Schedule
for more about servicing
this filter.
Alcohol Injector (Option)
If your vehicle has air brakes, it may have an alcohol
injector. It is on the frame or crossmember at the right
front corner of the vehicle.
The alcohol injector helps prevent moisture in the air
brake system from freezing. Use it only in cold weather,
32 _ F (0 _ C) or below.
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