Another compressor problem

[Pete Masterson]

That is correct. The brake system has no electrical components other
than the switches that turn on/off the tail lights. All control and
actuation is done through air pressure changes as controlled by
various valves. Similarly, the air bags (suspension) also have no
primary electrical components other than the valves that 'dump' the
air and sensors that report pressure, or lack thereof, to the buzzers
and dash panel gauges.

A total electrical failure should not cause you any immediate
problems in the safe handling or braking of your coach -- at least,
not from either the brakes or suspension components.

The other air operated items may have an electrically operated valve,
such as the stair-well cover, the air-step, the bulk oil filler, the
dump valves, and the dryer vent. Each of these has an electric switch
that actuates an electrically operated valve to activate/deactivate
the item. The air-step has a microswitch (under the coach) that can
be a problem if it becomes clogged with dirt or otherwise is moved
out of position.

The main braking system is partially isolated from the non-essential
appliances, but leaks in the auxiliary systems can lead to an
eventual loss of brake pressure or the inability to air up the coach.

When the air system is working properly, the coach should remain
charged with air for several hours after shutting down, if the
suspension isn't dumped. Frequent cycling of the air step will
deplete the air more quickly. If the system doesn't hold air for 6 to
12 hours (or more), then it's time to go over all the air-actuated
systems to hunt for leaks. Note: this is _much_ longer than the
standard required by most DMVs. Here's the CA DMV air brake check
procedure:

In-Cab Air Brake Check

NOTE: All items marked with an asterisk (*) are critical parts of the
in-cab air brake test and must be demonstrated during DMV testing.
They may be performed in any order. If these items are not performed
correctly, it is considered an automatic failure of the pre-trip test.

Test air leakage rate. (* second test only)

* With a fully-charged air system (typically 125 p.s.i.), turn off
the engine, release the service brake (brakes off), and let the
system settle (air gauge needle stops moving). Time the air pressure
drop. The loss rate should not be greater than:
— 2 p.s.i. or less in one minute for single vehicles.
— 3 p.s.i. or less in one minute for a combination of two vehicles.
— 5 p.s.i. or less in one minute for a combination of three or more
vehicles.
If the loss is too much, check for air leaks and fix.

* With roughly a fully charged air system (typically 100-125 p.s.i.),
turn off the engine. Release all brakes and allow the system to
settle (air gauge needle stops moving). Then apply full steady
pressure to the brake pedal (brake on) and hold. After the system
settles again, the air loss should not be more than:
— 3 p.s.i. or less in one minute for single vehicles.
— 4 p.s.i. or less in one minute for a combination of two vehicles.
— 6 p.s.i. or less in one minute for a combination of three or more
vehicles.
If the air loss is too much, check for air leaks and fix. For testing
purposes, identify if the air loss rate is too much.

*Check air compressor governor cut-out pressure. Pumping should start
at about 100 p.s.i. and stop at about 125 p.s.i. (130 p.s.i.
maximum). Run the engine at a fast idle. The air governor should cut-
out the air compressor at about the manufacturer's specified
pressure. The air pressure shown by your gauge(s) will stop rising.
For testing purposes, identify when the compressor cuts out.

*Check air compressor governor cut-in pressure. Start with the air
pressure above the governor cut-in level (no lower than 85 p.s.i.).
With the engine idling, slowly pump the brake pedal to reduce the air
tank pressure. Watch the air gauge between pumps to identify when the
compressor cuts in (needle starts to rise). This should be at about
the manufacturer's specified cut-in pressure. If the air governor
does not work as described, it may not keep enough air pressure for
safe driving. For testing purposes, identify when the compressor cuts
in.

NOTE: To perform this test correctly, the compressor cannot already
be pumping air. If it is, allow the governor to cut-out before
performing this test.

A full discussion of air brakes and their operation from the CA DMV
Commercial Drivers License booklet can be seen at:
<http://www.dmv.ca.gov/pubs/cdl_htm/sec5_a.htm>

Pete Masterson
'95 Blue Bird Wanderlodge WBDA 42
El Sobrante CA
aeonix1@...



On Dec 31, 2007, at 7:49 AM, Gregory OConnor wrote:

> <snip>
> I do not believe that any component of the air brake system is
> electrical.
>


[Non-text portions of this message have been removed]