CONDITION

POSSIBLE CAUSE

SOLUTION

Dryer leaks from purge
valve during compressor
loaded cycle. The leak may
cause excessive
compressor cycling or
prevent the system from
building air pressure.

Purge valve frozen open (cold weather operation).

Regeneration cycle too
long (more than 30
seconds), accompanied by
loss of pressure in the
supply tank.

Outlet check valve not seating.

Inspect and replace outlet check valve as needed.

Regeneration cycle too
short (less than 10
seconds).

High air system demands during compressor unloaded cycle.
Air governor not working properly.

Increase air system capacity or reduce air demands.
Inspect per manufacturer’s instructions and repair/replace as needed.

Air dryer purges too often,
perhaps as frequently as
every 15 seconds,
accompanied by excessive
cycling of the compressor.

Leak in line between governor and dryer port 4.
Excessive air system leaks.
Excessive air system demands.
Outlet check valve not sealing.
Air governor has less than 16 psi range.
Leaking air compressor unloader(s).
Loose governor or leak at governor gasket.

Repair air line.
Repair leaks.
Increase air system capacity or reduce air demand.
Inspect and replace outlet check valve as needed.
Replace air governor.
Inspect compressor. Repair/replace per manufacturer’s instructions.
Replace gasket and retorque fasteners.

Air dryer does not purge
when compressor unloads
(no blast of air from purge
valve).

Air line between governor and air dryer port 4 kinked or plugged.
Purge valve stuck closed.
Air governor not working properly.
Cut-out pressure never achieved by air compressor.

Repair air line.
Replace purge valve.
Inspect air governor. Repair/replace per manufacturer’s instructions.
Check for air leaks in system and repair as needed. If no leaks in system, check
compressor output. Repair/replace per manufacturer’s instructions.

Rapid “spitting” of air from
purge valve in small
amounts. Frequency varies
with engine speed.

Holset E-Type compressor used, but non-1200E dryer installed.
Compressor not completely unloading when cut-out pressure is
reached.
Normal for non-TCV air dryers.

Replace air dryer with an SS1200E air dryer.
Inspect compressor. Repair/replace per manufacturer’s instructions.

Air leak at turbo cut-off
valve vent. Hole burned in
piston.

Temperature of air coming into dryer is too high — not enough
cooling takes place before dryer inlet.

Move dryer farther from compressor. Add additional compressor discharge line
before air dryer. Add cooling coil or heat exchanger before air dryer.
NOTE: Inlet air temperature must not exceed 175°F (80°C).
Install lip seal correctly.

Debris under purge valve seat, such as particles from fittings or air
inlet line.
Purge valve washer installed upside-down.
Wrong air line connected to dryer port 4 (unloader port).
Purge valve snap ring not fully seated in groove.

Lip seal installed upside-down on piston. Lip must face UP (towards
dryer).
Valve bore worn excessively.
Piston is broken.
Air dryer frozen (water
collecting in base of dryer
is freezing).

No electrical power to heater connector.

Low voltage to heater connector.
Heater assembly not working.
Wrong voltage air dryer used; i.e., 12-volt air dryer used in a 24-volt
system.
No air pressure build-up in
system.

Air dryer not plumbed correctly (connections reversed).
Wrong air line connected to dryer port 4.
Air governor not working properly.
Air system leaks, such as compressor discharge line, air dryer,
reservoirs, brake or suspension valves, etc.
Air dryer leaks from purge valve.

Check heater. Repair/replace if necessary. Make sure governor to dryer port 4 line
is free of water/oil. Remove and inspect purge valve and clean water/oil from top
of piston.
Disassemble and clean purge valve. Remove cartridge and clean dryer sump area.
Ensure lip on aluminum washer faces down, away from dryer.
Verify correct air line installation and correct as needed.
Seat snap ring fully into groove.

COMPRESSOR
INTAKE LINE
SIGNAL LINE

SYSTEM RESERVOIR

COMPRESSOR
CHECK
VALVE

Inspect valve bore for wear. If a new turbo cut-off valve does not seal in a clean,
lubricated bore, replace the air dryer.
Replace the turbo cut-off valve.
Check for a blown fuse. Repair heater circuit.
NOTE: There must be power to the heater connector the entire time the
vehicle’s ignition is “on.”
Repair cause of low voltage, such as poor electrical ground, bad connections,
corroded wire splices, etc.
Replace heater assembly.
Replace with correct voltage air dryer.
Ensure compressor discharge line is plumbed to air dryer port 1, and air dryer port
21 is connected to vehicle’s supply tank.
Ensure dryer port 4 line is connected to the “UNL” port of the air governor.
Inspect governor per manufacturer’s instructions. Repair or replace as needed.
Locate leak(s) and repair.
See purge valve conditions listed in this chart.

Water, oil, or sludge in air
system tanks.

Desiccant contaminated with oil.

Replace desiccant. Inspect compressor per manufacturer’s instructions.

Water in system tanks,
everything else checks out
okay.

Dryer not suitable for application.

Review application guidelines. For assistance, call the Meritor OnTrac™ Customer
Call Center at 866-OnTrac1 (668-7221).

For more information, see Maintenance Manual 34 or dial our toll-free number: 866-OnTrac1 (668-7221).

TP 1033

System Saver 1200 Plus
Series Air Dryers

Revised 03-16
16579

COMPRESSOR
DISCHARGE
LINE

PURGE VALVE
(EXHAUST)

SYSTEM RESERVOIR
SUPPLY TANK

DESICCANT CARTRIDGE

COALESCING CARTRIDGE

DATE CODE INFORMATION
Date Code
First 2 Digits = Build Week
Last 2 Digits = Build Year

R950011

R950068

Manufacturing
Location Code

WABCO
1696

PRESSURE RELIEF VALVE
I.D. Tag No.
Note: A Part Number with an "S"
In Front of It Indicates a Rockwell
WABCO Service Part Number.

S2206-D-1226

OUTLET CHECK
VALVE
GOVERNOR

S432 470 920 2
S432 470 922 2

HEATER
PURGE VALVE
TURBO
CUT-OFF VALVE

12 VOLT – R950015
24 VOLT – R950016
R950014

S432 470 921 2