Possible Cause


Dryer is leaking from purge valve during compressor loaded cycle. Excessive compressor cycling or failure to build air pressure may occur.

Purge valve is frozen open due to cold temperatures.


Debris, such as particles from the fitting or air inlet line, under the purge valve seat.


Purge valve washer installed upside-down.


Wrong air line connected to dryer port 4 (unloader port).


Purge valve snap ring does not sit fully in the groove. 

Inspect the heater and repair or replace as needed. Make sure the governor to dryer port 4 line is free of oil and water.


Disassemble and clean the purge valve. Make sure the purge valve is free of water and oil from the top of the piston.

Remove cartridge and clean the dryer sump.


Make sure the lip on the aluminum washer is facing down and away from the dryer.


If necessary, correct the air line installation.


Ensure the snap ring is fully seated in the groove.

Slight leak from the purge valve, making the supply tank empty after several hours.

Outlet check valve not seating or regeneration valve not shutting off regeneration airflow.

Remove and inspect the outlet check valve and regeneration valve diaphragm. Clean if necessary and replace if worn or damaged.


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

Outlet check valve not seating.


Regeneration valve not closing off regeneration air flow correctly.

Inspect and replace outlet check valve if necessary.


Swap regeneration valve.

Too short of a regeneration cycle (less than 10 seconds).

During the compressor unloaded cycle, high air system demands.


Pressure-controlled check valve not installed or not working properly.


Wrong (One-way) check valve installed in system reservoir instead of, or with, pressure-controlled check valve.


Faulty Regeneration valve.


Faulty Air governor.



Air system capacity could be increased or reduce air demands.


Check or replace the pressure-controlled check valve, if necessary.


Remove the one-way check valve and ensure proper installation of pressure-controlled check valve.


Remove the regeneration valve. Ensure that the diaphragm is clean and free of oil and other debris. If no impurities are present, replace regeneration valve assembly.


Inspect and repair or replace as needed, per manufacturer’s instructions.

No regeneration cycle. After the initial purge blast no airflow (dyer decompression).

Air dryer is not connected to the supply tank or the connections were reversed.

Faulty regeneration valve.

Incorrect (One-way) check valve installed in supply tank.


Alcohol evaporator installed between dryer and supply tank.

Ensure that the dyer was installed correctly, per the system diagram.


Swap regeneration valve.


Take out the one-way check valve.


Install a bypass line around the evaporator or remove the evaporator from the system.


Air dryer purges too frequently, possibly as often as every 15 seconds, along with excessive cycling of the compressor.

Leak in line between governor and dryer port 4.


Leak in line between supply tank and governor.


Air system leaks excessively.


Excessive air system demands.


Outlet check valve not sealing.


Regeneration valve not shutting of properly.


Less than a 16 psi range on air governor.


Air compressor unloader(s) leaking.

Repair air line.


Repair leaks.


Increase air system capacity or decrease air demand.


Inspect and replace outlet check valve if necessary.


Replace regeneration valve.


Replace air governor.


Inspect compressor. Repair or replace compressor if necessary and per manufacturer’s instructions. 

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

There is a kink or plug in the air line between governor and air dryer port 4.


Purge valve wedged closed.


Air governor not working properly.


Cut-out pressure never reached by air compressor.



Repair air line.


Replace purge valve.


Inspect air governor and repair or replace per manufacturer’s instructions.


Check for air leaks and repair if necessary. If there are no leaks in the system, check the compressor output and repair or replace per manufacturer’s instructions.

During entire duration of compressor being unloaded, air flows out of the purge valve.

Turbo cut-off valve not sealing.

Replace the turbo cut-off valve.

Small amounts of air “spitting” from purge valve rapidly. Frequency varies with engine speed.


Non-1200E dryer installed, but Holset E-Type compressor used.


Compressor not unloading completely when cut-out pressure is reached.

Replace with a System Saver 1200E air dryer.


Inspect compressor and repair/replace per manufacturer’s instructions.

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

Temperature of air coming into the dryer is too high – not enough cooling occurs before dryer inlet.

Move the dryer farther from the compressor. Add additional compressor discharge line before air dryer. Add cooling or heat exchanger before air dryer.

(Note: Inlet air temperature must not exceed 175°F)


Air leak at turbo cut-off valve vent.

Lip seal installed upside-down on piston (lip must face up towards dryer).


Overly worn valve bore.

Install lip seal facing up towards dryer.


Inspect the valve bore for wear. If a new turbo cut-off valve does not seal in a clean, lubricated bore, replace the air dryer.

Air dryer frozen (water in the base of the dryer is freezing).

Low voltage  or no electrical power to heater connector.


Heater assembly now working.


Wrong voltage air dryer used (for example, 12-volt air dryer used in a 24-volt system).

Check for a blown fuse and repair heater circuit if necessary.

Note: During the entire duration that the vehicle ignition is “on”, there must be power to the heater connector.


Look for signs of low voltage, such as poor electrical ground, bad connections corroded wire splices, etc. and repair.


Replace heater assembly.


Replace with correct voltage air dryer.

No air pressure build-up in system.

Air dryer not plumber correctly (connections reversed).


Dryer port 4 connected to wrong air line.


Air governor not working correctly.


Air system leaks, such as compressor discharge line, air dryer, reservoirs, brake or suspension valves, etc.


Air dryer leaks from purge valve.

Make sure that air dryer port 1 is plumbed to compressor discharge line, and air dryer port 21 is connected to vehicle’s supply tank.


Make sure that dryer port 4 line is connected to the “UNL” port of the air governor.


Inspect governor per manufacturer’s instructions and repair or replace if necessary.


Find the leak(s) and repair.


See purge valve conditions listed in this chart


Water in tanks; this usually occurs as a result of aftermarket installation or when dryer is a replacement for a competitive brand.

Pressure-controlled check valve not installed in correct tank or not installed at all.


Pressure-controlled check valve installed correctly, but one-way check valve not removed.

Install pressure-controlled check valve in secondary tank.


Remove one-way check valve so that only the pressure-controlled check valve is installed between the secondary tank and supply tank.

Water, oil or sludge in air system tanks.

Desiccant contaminated with oil.


Non-1200E dryer installed, but Holset E-type compressor used.

Replace desiccant. Inspect the compressor per manufacturer’s instructions.


Replace air dryer with a System Saver 1200E air dryer.

Water in system tanks, everything else is fine.

Dryer not suitable for application.

Review application guidelines.