3 Troubleshooting and Testing
31
Meritor WABCO Maintenance Manual 34 (Revised 03-16)
Tests
Heater Resistance
1. Set volt-ohmmeter to ohms.
2. Disconnect the vehicle harness at the heater.
3. Place leads on the two pins on the heater connector at the air
dryer.
4. Check the resistance. A resistance of 1.0-2.0 ohms should be
seen for a 12-volt heater assembly and 5.0-7.0 ohms should
be seen for a 24-volt heater assembly.
앫 If there is correct resistance on the dryer side and
there is voltage at the harness: The heater is functioning
correctly. Reinstall the components and harness.
앫 If resistance is less than 1.0 ohm for a 12-volt heater
assembly or 5.0 ohms for a 24-volt heater assembly:
Replace the heater.
To avoid damaging components, Meritor WABCO recommends
performing this resistance check with the heater in place.
NOTE: The dryer temperature must be in thermostat closed range
(below 35°F) in order to check heater resistance.
Electric Power to Dryer
1. Set the volt-ohmmeter to volts.
2. Disconnect the vehicle harness at the heater.
3. Place leads on each pin of the wiring harness connector.
4. If there is an abnormal voltage reading, inspect the wiring
harness, wires and fuses.
Leak Test
1. Drain air from all system tanks.
2. Close reservoir draincocks.
3. Start the vehicle. Allow air system pressure to build while
engine idles.
4. When the system reaches cut-out pressure there will be a
purge, or strong blast of air, followed by a mild flow which will
last 10-45 seconds.
5. Shut off the engine.
6. Apply a soap solution to each connection that contains
pressurized air. Check the connections to see if soap solution
bubbles.
No Soap Bubbles: Connections are sealed properly.
Soap Bubbles Appear: Connections are NOT sealed properly.
To Repair Incorrectly Sealed Connections
1. Drain all reservoirs.
2. Remove leaking connection.
3. Inspect the connectors and ports for damaged threads or
cracks. Replace if necessary.
4. Apply pipe sealant to the connection.
5. Repeat leak test until all connections are sealed.
Air Pressure Checks
NOTE: When checking air pressure during these tests, do not rely
on cab air gauges for accurate readings. Install a calibrated air
gauge, accurate to within one psi (7 kPa), in the secondary air tank
to determine if air pressure is within the required ranges.
Operational Test for System Saver Series Air
Dryers — Regeneration and Purge Style
1. Check compressor loaded and unloaded cycle. Figure 3.2.
Figure 3.2
When the compressor is in the loaded cycle, air pressure will
build to approximately 120-140 psi (827-965 kPa) (cut-out
pressure). When the compressor reaches the unloaded cycle,
the air dryer will purge, initiating regeneration of the air dryer.
2. For regeneration style air dryers, the regeneration cycle, which
lasts from 10-35 seconds, the supply and secondary tanks will
drop approximately 10 psi (69 kPa) in pressure. Check the
secondary air gauge on the vehicle dash panel to verify this
drop.
Figure 3.2
PSI
20
40
60
80
100
110
120
1002161a
PRIMARY
AIR SUPPLY
(RED)
SECONDARY
AIR SUPPLY
(WHITE)
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