Service manual

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AIR DRYER TROUBLESHOOTING CHART

SYMPTOMS

1. Dryer is constantly

“cycling” or purging.

Dryer purges frequently

(every 4 minutes or less

while vehicle is idling).

A. If leakage IS SHOWN on gauges test for

excessive service brake system leakage.

Allowable leakage:

Pre-121 vehicles, single vehicles - 2 psi/

minute.

Tractor trailer - 3 psi/minute.

121 vehicles, single vehicle - 1 psi/minute per

service reservoir.

Tractor trailer - 3 psi/minute per service

reservoir. Repair and retest as required.

If leakage is NOT SHOWN on gauges test for

excessive supply system leakage.

A. Excessive system

leakage. IMPORTANT:

Note whether air

pressure loss is shown

on dash gauge(s).

Pressure loss shown on

gauges is caused by

service brake system or

component leakage.

Pressure loss NOT

SHOWN on gauges is

caused by supply

system or component

leakage.

CAUSE

REMEDY

Remove drain cock or valve in supply reservoir (wet

tank) and install air gauge. Build system pressure,

allow air dryer to purge and observe air gauge in

supply reservoir. Pressure drop should not exceed 1

psi per minute. Perform tests 1 to 6 in the order

presented.