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Air drier

AIRDRY-E
Air drier, general
The new electronic air drier works according to the same principles as it's air-controlled predecessor. The
difference is that the new air drier is controlled electronically. If the air drier should for some reason become
powerless, it will cease to function and the desiccant will become wet through, while the compressor will continue
to charge. Relief is provided via the safety valve.

By using the information from the vehicle electronic system, the air drier and compressor control can be
optimised, so that drying of the air is guaranteed and fuel consumption is reduced. The air drier has a built-in
function to prevent freezing or blockage. The function provides temporary relief (air drier blow clean) at engine
shut down. This function eliminates the problem of freezing on a stationary vehicle.

Air drier, overview

A: Compressor. B: Cooling coil. C: Air drier D: Vehicle control unit. E: Air system. F: Solenoid valve, regeneration
(Y51A). G: Solenoid valve, relief (Y51B). H: Electrical control signal, relief. I: Electrical control signal,
regeneration. J: Check valve. K: Data links: 1587/1939. The following values are obtained from these links:
System pressure, engine speed, engine elapsed time, ambient temperature and vehicle speed.

Wiring diagram

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z 1 = From compressor
z 2 = To air system (air tanks)
z 3 = Evacuation
z 4 = Control signal to compressor
z 5 = Air filter
z 6 = Drier filter
z Y51A = Solenoid valve, regeneration
z Y51B = Solenoid valve, relief (compressor control)

The working phases of the air drier

Flow diagrams of the driers' working phases are shown below.

Charging phase

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A = Damp input air from compressor

B = Dried air

Relief phase (without regeneration)

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A = The input air from the compressor is fed

directly to the outlet port and out through the
silencer (C).

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B = A check valve retains the pressure in the

system.

D = Control signal (control air) to compressor.

Regeneration phase

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A = The input air from the compressor is fed

directly to the outlet port and out through the
silencer (C).

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B = A check valve retains the pressure in the

system.

D = Control signal (control air) to compressor.

E = Dry air from the tanks is fed backwards up

through the desiccant cartridge via a solenoid
valve (Y51A).

F = Water, dirt and oil from regeneration are fed

out through the silencer (C).

Electronic air drier functions

Drier control

Icon on display

General

A function controls the regeneration of the air drier and ensures that the air fed to the vehicle compressed air
system is dry, even after long charging periods.

The monitoring strategy works by the system monitoring the pumped air volume (charge phase) and regeneration
(return flow from the system) depending on this volume. There is no longer a separate regenerating tank.

Regeneration

After the charging phase is complete, the air drier is regenerated (dried) by a certain amount, approx. 12%, of the
pumped air, being fed back from the compressed air system through the air drier and out via the silencer in the
bottom. This functions according to the following principle: If 100 litres of air is pumped out, then 12 litres shall
flow back (1000/120) etc.

If the compressor has pumped a larger volume or air, the pressure will drop to the engagement pressure before
the required volume of air has flowed back. The compressor then starts again and pumps until the disengagement
pressure is reached and a regeneration is started. In this way, a number of compressor charges and
regenerations will be performed after each other automatically until the required volume of air has flowed back.
This can continue for a longer period of time (up to a half hour) and is completely normal! The regeneration
volume controls how the air drier operates. See the diagram below, which shows the compressor's work and the
air pressure in relation to the regeneration volume.

The vehicle control unit, which controls the air drier and compressor, registers how much air needs to flow back
after each compressor charging. It does this even after engine shut down.

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Symbols in Description
diagram
Note: The pressure levels below apply to a vehicle with air suspension.

A Air consumption 1; the compressor pumps for about 10 minutes to a pressure of 8 bar.
Example: The vehicle loads the first swap body

B Regeneration phase 1; air consumption has ceased, the drier is regenerated and the
pressure increases and decreases alternately in rapid succession. The drier is not fully
damp and the vehicle drives with max. 30 km/h - the pressure alternates between 12
and 10.6 bar.
Example: The vehicle drives slowly to pick up the other swap body.

C Air consumption 2; the compressor pumps for about 10 minutes to a pressure of 8 bar.
Example: The vehicle loads the other swap body.

D Regeneration phase 2.1; air consumption has ceased, the drier is fully damp
(regeneration volume >360 l) and the vehicle drives at max. 30 km/h - the pressure
alternates between 12 and 10.1 bar.
Example: The vehicle drives slowly away from the load zone.

E Regeneration phase 2.2; The drier is no longer fully damp (regeneration volume<360 l)
and the vehicle is still driving at max. 30 km/h - the pressure alternates between 12 and
10.6 bar.

F Regeneration phase 2.3; The vehicle drives faster than 30 km/h - the pressure has
dropped to the high speed range and alternates between 10.6 and 9.6 bar.

G Relief phase 1; the drier is completely dry (regeneration volume<50 l at high speed)
and the vehicle uses no air, so the pressure remains at 10.6 bar which is the relief
pressure for high speed (>30 km/h).

H Relief phase 2; the drier is still completely dry (regeneration volume<100 l at low speed)
and the vehicle uses no air. The speed has now dropped to <30km/h so the pressure
has increased to 12.0 bar, which is the relief pressure for low speed (<30 km/h).
This secures full air pressure in the tanks before the next load handling.

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P System pressure
R Regeneration volume (can be read off with VCADS-PRO)
V Level of regeneration volume (360 l) when fault code PPID 430 is set in MID 144,
vehicle control unit.

System pressure

The air pressure is always sufficient for brake operation and lifting of the air suspension. Below 10.1 bars
pressure, charging will be the first priority. Above 10.1 bars pressure, regeneration will be the first priority,
however, with high air consumption, regeneration time will be short. In practice, this can mean that a temporary
air pressure somewhat lower than 10.1 bar may occur, since it can take a few seconds to stop a regeneration that
is in progress. See the table below for cut-in and cut-out pressures for different variants:

Low speed/stationary High speed >30 km/h

Cut-in pressure Cut-out Cut-in pressure Cut-out

pressure pressure

Normal Wet Normal Wet

Variant mode condition* - mode condition* -

ASCOP85 7.5 bar 7.5 bar 8.5 bar 7.5 bar 7.5 bar 8.5 bar
Leaf springs
ABS/UABS
21030180

ASCOP120 10.6 bar 10.1 bar 12.0 bar 10.6 bar 10.6 bar 12.0 bar
Leaf springs
EBS
21030175

ASCOP100 9.0 bar 9.0 bar 9.8 bar 9.0 bar 9.0 bar 9.8 bar
Japan
20565846

ASCOP120 10.6 bar 10.1 bar 12.0 bar 9.6 bar 9.6 bar 10.6 bar
Standard
-

ASCOP120 10.6 bar 10.6 bar 12.0 bar 10.6 bar 10.6 bar 12.0 bar
High Pressure
set-up
20544779

*) PPID 430 active, regeneration volume >360 litre

Memory for undried air

For additional improvement of the drying function, the memory for the volume of undried air at each engine shut-
down (starter key turned to 0 position) is increased . With repeated turning of the starter key between drive and 0
positions (i.e. when downloading software) the memory for undried air can be so large that forced regeneration
will occur at the next engine start. Therefore do not turn the starter key unless necessary.

When downloading software for several control units, it is best to update the vehicle control unit last.

Compressor control

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General

The function controls the connection and relief periods of the compressor, while at the same time reducing fuel
consumption by allowing the compressor charging periods to occur preferentially when descending gradients or
decelerating. As a side effect, the lifespan of the compressor is increased since the average pressure in the
system is lower.

System pressure

At vehicle speeds below 30 km/h, full system pressure is allowed, to guarantee that the air tanks are completely
filled prior to the vehicle entering a load depot.

At speeds over 30 km/h a reduced system pressure applies, except when descending inclines or braking (no fuel
injection) when full system pressure is allowed, i.e. the system can be filled when charging does not require any
energy from the engine.

To improve the starting characteristics of the engine, the compressor is unloaded during starting, assuming that
the system pressure is above 7 bar.

To avoid freezing or blocking of the air drier while the engine is turned off, a temporary unloading is performed (air
drier blow through) at engine switch off. The unloading is only performed if the system pressure is above 7 bar.

A yellow warning light illuminates if the system pressure exceeds 13 bar.

Service checks

Icon on display

General

This function helps the service personnel and vehicle owner to plan servicing and component exchange and
thereby reduces costs. On most of today's vehicles, the desiccant is changed too often or too seldom, which
results in high costs and poor functionality. On the electronically controlled air drier, an icon is displayed (see
figure) and a yellow warning lamp lights when it is time to change the desiccant.

Reading off information with VCADS-PRO

By using VCADS-PRO it is possible to read off the calculated remaining mileage to the next desiccant
replacement. The total pumped air volume for the compressor can also be read off.

The charge air volume is calculated from the charging time, system pressure and rotational speed.

Adaptation to driving style

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If there is a problem with water in the tanks due to large air consumption, the parameter CUB can be set to 15%
(standard is 12%) by using VCADS-PRO. This increases the volume of air that must flow back through the
desiccant and increases the drying capacity.

Calibration when replacing desiccant cartridge

When replacing desiccant or the compressor, calibration shall be performed (zero running time). When changing
to another size of compressor, the parameter data must be altered. All calibration and alteration of parameter data
is done with VCADS-PRO.

Customers who do not wish to perform calibration when changing desiccant holders, can by using VCADS PRO:
turn off this function. This however excludes the possibility of reading off the remaining mileage to the next
desiccant replacement.

To ensure good air quality, both with regard to dampness and oil content, it is important that the correct
type of desiccant cartridge is mounted. Volvos desiccant cartridge contains, in addition to desiccant, an
oil filter.

Air leakage check/warning

Icon on display

The purpose of this function is to inform the driver that the compressor is charging abnormally, which is usually an
indication of an air leak, by using an icon (see figure) and a lamp on the display.

Two levels of warning are given. A white information lamp indicates increased fuel consumption. A yellow warning
lamp plus an icon indicates a risk for increase compressor and air drier wear, which can lead to unplanned stops
if the fault is not corrected.

The check is only performed when driving faster than 50 km/h and when the wheel brakes are not in use.

Managing fault codes

This function handles presentation of fault information. Both direct hardware faults and faults detected via the
logic in the software are displayed. For the faults stated, an icon is displayed and a warning lamp is lit. Fault
presentation (under vehicle control unit) follows the previous architecture for handling fault codes. The fault codes
are described in service information Vehicle control unit, fault codes under function group 36.

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