OPERATION MAINTENANCE SERVICE MANUAL
GEARED FOR INNOVATION SINCE 1960

AIRFLEX® AIR RIDE SUSPENSION SYSTEM

www.dexteraxle.com

www.dexteraxle.com
2900 Industrial Parkway East n Elkhart, IN 46516
Phone: 574-295-7888 n Fax: 574-295-8666

ISO 9001 Certified

www.dexteraxle.com

04/17

© 2016-2017 Dexter Axle Company. LIT-011-OO

Introduction
This manual is designed to provide information for you to understand,
use, maintain, and service your trailer running gear system. Your axles are
manufactured by Dexter. Since 1960, Dexter’s experience in the design,
testing, and manufacturing of trailer axles has resulted in the most complete
product line in the industry. The Dexter running gear system consists of
axles, suspensions, and braking systems which are engineered to provide
you the finest towing and stopping performance available today.
Two Dexter philosophies are at work to provide you the best product
available and have enabled us to maintain our position of leadership. First,
we operate on the theory that “there is always a better way” for a product
to operate, to be manufactured, and/or to be serviced. We are constantly
striving to find that better way.
Secondly, we maintain the highest quality control standards in the industry
and adhere to ISO 9001. Dexter has operated with detailed documented
processes and procedures long before completing ISO Certification,
continually placing quality and customer service as the focus. This ensures
that critical components including axle beams, hubs, drums, spindles, and
braking systems are manufactured to the highest quality standards so
that we can provide our customers with dependable products, the most
comprehensive product offering and reliable, consistent customer service.
Trusting is hard. Knowing who to trust even harder. Through vertical
integration we engineer, design, manufacture and test virtually every part
in-house to ensure superior quality trailer running gear. We fuss over
details, so you don’t have to. Trust Dexter.
Visit us online at www.dexteraxle.com.

Contents

Table of Contents

AC-019 Air Supply and Control Kit.............................................3
Enclosure.............................................................................3
Compressor.........................................................................3
Air Reservoir........................................................................4
Relay Switch........................................................................4
Circuit Breaker.....................................................................4
Reservoir Drain Valve...........................................................4
Manual Fill Valve..................................................................4
Pressure Switch...................................................................5
Air Gauge.............................................................................5
System On-Off Toggle Switch..............................................5
Trailer Raise-Lower Valve.....................................................5
Tube Fittings.........................................................................6
Instructions for Front Pivot Bushing Replacement...............6
AC-016 Height Control Valve Kit ................................................8
Height Control Valve.............................................................8
Normal System Operation..........................................................9
Starting the System.............................................................9
Troubleshooting Guide..............................................................11
System Won’t Start............................................................11
Trailer Won’t Rise to the Proper Height..............................11
Compressor Will Not Shut Off............................................12
Air System Will not Build Pressure.....................................12
Compressor Overheats and Circuit Breaker Opens...........12
The System..............................................................................13
The Electrical System........................................................13
The Pneumatic System......................................................13
Air Supply and Control Enclosure.............................................14
Air System Diagram With 12 VCD Compressor........................15
Ride Height Installation Procedure...........................................16
Limited Warranty.......................................................................18
Dexter Video Gallery................................................................21

-2-

CAUTION

This is the safety alert symbol. It is used to alert you to
potential injury hazards. Obey all safety messages that
follow this symbol to avoid possible injury or death.

AC-019 Air Supply and Control Kit
The kit enclosure is a 12" x 12" x 5" stainless steel box that
contains the 12 Volt Air Compressor, Air Reservoir, Relay Switch,
Circuit Breaker, Reservoir Manual Drain Valve, Manual Air Fill
Valve, Pressure Switch, Air Gauge, System On-Off Toggle Switch,
Trailer Raise-Lower Valve, and 50 feet of each of the color coded
air lines that are needed for the installation on the trailer. The air
fittings are also color coded to make it easy to plumb or trouble
shoot the system.

Enclosure
The solid stainless steel enclosure box comes completely
assembled, fully tested electrically and pneumatically for proper
operation. The box must be mounted vertically on a wall or
bulkhead with the manual drain valve and fittings on the bottom.
There are predrilled flanges on each side of the enclosure to
allow easy attachment to the trailer. If it is ever necessary, the rear
cover can be easily removed. To remove the rear cover, unbolt the
system from the trailer and unbend the tangs of the rear cover
which stick through the flanges of the enclosure.

Compressor
The 12 Volt DC air compressor provides compressed air for
operating the air suspension. It is rated for intermittent duty with
a 30% duty cycle; for example, 13 minutes on and 30 minutes
off. The compressor motor is internally thermally protected with a
circuit breaker that will automatically reset when the motor cools
down. This is a very reliable unit with many years of history in this
type of application.

-3-

AC-019 Air Supply and Control Kit

!

Air Reservoir
The purpose of this air reservoir tank is to prevent rapid on‑off
cycling of the compressor and to collect moisture, which
condenses from the compressed air so that it can be drained
from the system. Draining this water from the system protects the
air system from water damage and freezing damage to system
components. The reservoir should be drained each time the trailer
is operated. For reference, be aware that the reservoir air pressure
indicated on the gage on the front of the enclosure, is not the
same as the pressure in the air springs.

Relay Switch

AC-019 Air Supply and Control Kit

The relay is an electrically operated switch that turns on or off the
high current from the 12 Volt battery supply, which operates the
compressor. When the relay is energized by the on-off switch for
the system, the small current in the on-off switch that runs through
the pressure switch when system pressure is below 110 PSI
causes the relay to turn on the high current to the compressor.

Circuit Breaker
A 30 AMP circuit breaker protects the compressor and other
electrical components from electrical overloads or short circuits.
The circuit breaker automatically resets when the overload or
short is eliminated and it cools.

Reservoir Drain Valve
The reservoir drain valve has a manually operated metal pull
cable. To drain moisture from the reservoir, pull the cable. When
the trailer is being used, this should be done at least once per day
or each time the trailer is operated.

Manual Fill Valve
The manual fill valve is furnished for use in the unlikely event that
the air supply system fails to function. Simply fill the air system
from a typical tire compressor. External fills are only effective for
a short distance. The air will bleed off as the height control valve
operates. The trailer may still be operated without the air supply.
Without air, the rubber torsion suspension is not as soft as the
air suspension, but is still a very effective backup suspension
providing some level of vehicle and cargo protection.
-4-

The pressure switch is preset to close contacts and if the system
on-off switch is on, it will activate the relay switch and turn on
the air compressor at 110 PSI. At 145 PSI, the pressure switch
contacts open de-energizing the control circuit to the relay switch
and shutting off the air compressor. It is important to note: THESE
PRESSURES ARE RESERVOIR PRESSURES, NOT AIR
SPRING PRESSURES.

Air Gauge
The air gauge displays the air pressure in the reservoir. It does not
display the air pressure in the air springs. Air spring pressure is
automatically controlled by the Height Control Valve based on the
load on the suspension.

System On-Off Toggle Switch
The system on-off toggle switch completes the circuit to the relay
switch through the pressure switch using very small current levels
to control the high current needed to operate the compressor. The
switch is lit when the system is turned on. The compressor may
not come on when the switch is turned on since the compressor
only runs when the pressure in the air reservoir drops below 110
PSI.

Trailer Raise-Lower Valve
The Raise-Lower valve is a rotary valve that is connected to the
output of the height control valve and to the line leading to the
air springs. When the control knob is rotated clockwise, the air
circuit to or from the air springs is connected to the center port
of the Height Control Valve and the height of the suspension is
automatically controlled by the Height Control Valve. When the
valve control knob is rotated counterclockwise, the line from the
center port of the height control valve is shut off and the line from
the air springs is exhausted to atmosphere through a muffler
attached to the valve lowering the suspension and trailer about
2¹⁄₂ to 3 inches. There are no connections to the valve within the
enclosure. The black tubing from the air springs is connected to
the rear-most port on the valve and the green line from the center
port of the height control valve is connected to the front-most port

-5-

AC-019 Air Supply and Control Kit

Pressure Switch

of the valve. When rotated, the valve knob must always be rotated
completely until it stops.

Tube Fittings
Tube fittings are premium stainless steel push-type fittings for
¹⁄₄" OD plastic tubing. Always be sure that the tubing is cut off
squarely on the ends and pushed all the way into the fitting,
otherwise the connection will leak. The tubing can be removed if
need be from the fitting by pushing in on the small ring on the end
of the fitting while pulling outward on the tubing.

Instructions for Front Pivot Bushing
Replacement
Notice to Buyer

AC-019 Air Supply and Control Kit

It is recommended that both pivot bushings be replaced at the
same time to ensure continued axle alignment. Additionally, each
side needs to be replaced while the other side remains intact to
maintain control over the suspension components.

Safety Precautions
It is recommended that if you are unfamiliar with this type of work,
you should refer to a qualified service center specializing in trailer
suspensions. It is also recommended that if you choose to do this
yourself, that a factory service manual be obtained for the proper
procedures pertaining to removal, replacement and proper torque
specifications for your vehicle. This instruction set is intended
as a guideline for the safe installation of Dexter’s polyurethane
bushings, once you have removed the factory components from
your vehicle.

!

CAUTION

Do not lift or support the trailer on any part of the axle
or suspension system. Never go under any trailer unless
it is properly supported on jack stands which have been
rated for the load. Improperly supported vehicles can fall
unexpectedly and cause serious injury or death.

-6-

Disassemble ¾" nut and bolt. Remove original rubber/
polyurethane bushings (you may need a punch for this) and
clear the Airflex® joint of any old rubber or rust. When installing
polyurethane bushings, apply grease as instructed.
1.

Apply light coat of grease to inside of the axle bracket
sleeve.

2.

Apply light coat of grease to the inside and outside of the
bushing (all parts that contact metal).

3.

Apply light coat of grease to the outside of the sleeve.

4.

Apply light coat of grease to the faces of the bushings after
they are installed.

Torque the ¾" pivot bolts to 270-280 Ft. Lbs. to prevent bushing
wear and/or suspension damage.
Lock Nut
006-287-00

5.72

Bushing
014-123-00

4.22

-7-

Sleeve
014-127-00

¾" Bolt
007-466-00

AC-019 Air Supply and Control Kit

Pivot Bushing Replacement
(K71-734-00 Kit for one Airflex® Axle)

AC-016 Height Control Valve Kit
This kit contains the Height Control Valve, all required fasteners,
brackets, and linkage. The Height Control Valve mounts to the
predrilled frame bracket and the free end of the pre-assembled
linkage attaches to the predrilled hole in the side of the lower air
spring beam.

Height Control Valve

AC-016 Height Control Valve Kit

The Height Control Valve controls the height of the trailer and air
spring air pressure automatically. When starting or after loading,
the Height Control Valve will, through a linkage, cause the valve
to open, allowing air to enter the air springs until the trailer rises
to the predetermined design height. The air spring air pressure
rises as the trailer load is increased. When the trailer is unloaded,
the trailer will rise due to the higher than needed air pressure in
the springs. When this occurs, the Height Control Valve will open
allowing the air springs to exhaust air until the trailer comes back
to the pre-determined design height. Normally, the trailer will raise
2¹⁄₂ to 3 inches from the air-exhausted height to the design height
for highway use.

-8-

Starting the System
Check around the trailer to be sure there are no people or
obstacles under or around the trailer.

!

CAUTION

Do not get under the trailer or in pinch points around
wheel wells at any time. Air suspensions can descend
suddenly and without warning, which can cause serious
injury or death.
1.

Rotate the system Raise-Lower valve counterclockwise to
the Lower position.

CAUTION
Be sure all items and people are clear of the descending
trailer.
2.

Turn the system On-Off toggle switch to the On position.
The compressor should come on.

3.

Allow the system air pressure to build to approximately 145
PSI. The compressor will automatically shut off at about
145 PSI.

4.

Rotate the system Raise-Lower valve to the Raise position.
The trailer should rise 2¹⁄₂ to 3 inches at the wheel wells.
When the trailer is at the proper height and the reservoir air
pressure is at about 145 PSI, the compressor will shut off.

5.

The trailer is ready for operation.

6.

When pulling the trailer, the compressor will come on from
time to time, more often in stop and go operation in the city.
This is normal; however the compressor should not run
constantly.

-9-

Normal System Operation

Normal System Operation

When parking for short periods of time, it is not necessary
to turn off the system. When stopping overnight or longer, it
is recommended that the trailer be lowered and the system
turned off to prevent running the battery down. The trailer
should be lowered and the system should be turned off
before disconnecting the trailer from the tow vehicle.

Normal System Operation

7.

-10-

System Won’t Start
1.

Check battery condition for full 12 Volt charge. Also check
ground, wire and battery connections.

2.

If connections are tight and battery is fully charged, it may
become necessary to open the air supply enclosure.

3.

Once the enclosure is opened using a multi-meter, check
the circuit breaker for continuity. If circuit breaker contacts
are open replace the breaker.

4.

Check On-Off toggle switch for proper operation. Check
switch contacts and proper wire connections.

5.

Check air pressure switch for continuity. If contacts are
open when air pressure is not present, replace the switch.

6.

Check electric relay switch for proper operation. Terminals
86 and 85 are connected to the relay coil windings and
should show continuity at all times. Contacts 87 and 30
are normally open and should close when 12 Volt power is
applied to contacts 86 and 85. Replace switch if this is not
the case.

Trailer Won’t Rise to the Proper Height
1.

If compressor has built air pressure to 145 PSI in the
reservoir, check to see if air pressure is in the blue line
going to the height control valve.

2.

If the blue line has air pressure, check the green line for air
pressure. If there is no pressure in the green line, check the
height control valve linkage for damage, wrong adjustment
or pinched tubing.

3.

If the green line has air pressure, check the black line for
pressure. If no pressure, check the Raise-Lower valve for
proper position. It must be rotated fully clockwise to the
raise position. If air does not flow through the valve when
the valve is in the proper position, check for proper airline
hook up and pinched tubing; replace the valve if necessary.
If the black line does have air pressure, check down stream
tubing for pinched tubing.

-11-

Troubleshooting Guide

Troubleshooting Guide

Compressor Will Not Shut Off:
1.

Replace the pressure switch if switch contacts do not open
when 12 Volt power is not present.

2.

Replace electric relay switch if contacts 87 and 30 do not
open when 12 Volt is not present.

Troubleshooting Guide

Air System will not Build Pressure to
145 PSI and Cause Pressure Switch to Open
1.

Turn Raise-Lower valve to the fully lower position. Turn
compressor on and allow time to build up reservoir
pressure. If compressor does not build to proper pressure,
check air lines and fittings on the blue and green tubes. If
these fittings and tubes are secure and no leaks are found,
open the enclosure and check tubes and fittings inside the
enclosure. If these are secure and no leaks are found, it
may be necessary to replace the compressor. Read and
follow all trouble shooting instructions found in the Viair
User Manual (280C Air Compressor part #28021) provided
with your system. A clogged air filter may also be the
culprit. Check it and replace or clean it.

2.

If the air system pressure builds to 145 PSI and shuts
off as it should when the Raise-Lower valve is in the fully
lower position, there must be an air leak downstream from
the Raise-Lower valve. With the compressor on, rotate the
Raise-Lower valve to the fully raise position.

3.

Check the air line fittings on the black tubing for leaks.

4.

Use water with soap to check for bubbles at air leaks.

Compressor Overheats and
Circuit Breaker Opens
1.

Check for the use of too small wiring size or loose wire
connectors or a loose ground connection. The compressor
will overheat if operated with a low voltage or a partially
discharged battery.

2.

Clean or replace the air filter.