THE FRONT AIRS UP OK THE BACK IS ALL THE WAY DOWN AND WAS ALWAYS UP UNTIL I UNHOOKED THE OLD DRYER TO REPLACE IT. WHAT COULD CAUSE THIS? THERE ARE NO LEAKS I CAN HEAR OR FIND AT THE DRYER NOR ANYWHERE ELES.
Maybe you got dirt in the line to the rear. Here's some background info:
The air suspension system includes the following major components:
All system functions are controlled by vehicle dynamics control module (5A919). This control module receives inputs from several different sources. These inputs include:
Communications monitor system operation and allow diagnosis of any concerns that may develop in the system.
The message center indicator will display AIR LEVELING DISABLED or CHECK RIDE CONTROL if the suspension system is not turned on or the vehicle dynamics control module detects a concern. If air leveling system disabled is displayed, check that air suspension service switch is in the ON position.
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Weight Added
When weight is added to the vehicle, the air suspension system responds as follows:
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Control Module Power and Ground
The vehicle dynamics control module (5A919) is located above the upper luggage compartment trim panel and lower module tray. Module power is provided by Circuit 418 (DG/Y) at Pins 36, 37, 56, 57, 58 and is powered through a Fuse 7 (30A) in power distribution box. Module ground is provided through control module wire harness Pins 6, 39, 40 and 60.
The data link connector (14489) (DLC) is located in the passenger compartment under the instrument panel, 300 mm (12 inches) right of the steering column. This connector allows communications between the vehicle dynamics control module and either Rotunda New Generation Star (NGS) Tester 007-00500 or equivalent or Rotunda Service Bay Diagnostics System (SBDS)® 001-00001 or equivalent.
When the CHECK RIDE CONTROL message is displayed in the message center indicator (10D898), a system error has been detected by the vehicle dynamics control module and is stored in the control module. This diagnostic trouble code (DTC) will be retained for the next 80 ignition switch cycles. If there is no repeat of the same error during these 80 ignition switch cycles, the control module will erase the DTC.
Because of this self-erasing memory, a customer may have had a concern "just a few days ago" that is not retrieved from memory when Diagnostic Test Mode (DTC) "Retrieve/Clear Continuous DTCs" is executed. This must be kept in mind if you must tell customer that no current concern has been found.
When the vehicle dynamics control module detects a concern, the air suspension system is disabled for the current ignition cycle. If the condition causing the concern clears up during the current ignition switch cycle, the system will not reactivate.
For example, if the customer has severely overloaded the luggage compartment, the system will not be able to trim the vehicle without exceeding the compressor run time. This will generate a DTC that disables the computer controlled suspension system. If the customer then drives the vehicle and unloads the luggage compartment without turning the ignition switch OFF, the system will not adjust for the new load. The customer will experience poor ride quality and the vehicle will not adjust trim.
more background
Air Compressor Assembly
NOTE: The compressor motor contains a thermal overload circuit breaker. Excessive temperature will trip the circuit breaker which resets automatically.
The air compressor assembly is located in the RH front of the engine compartment on the frame rail.
The air compressor has the following features and operates as follows: A single-cylinder piston-type electrically operated air compressor, mounted on the RH front fender apron, supplies the air pressure for operating the system.
A regenerative-type compressor air drier is attached to the compressor manifold.
All airflow during compression or venting passes through the compressor air drier.
A vent solenoid, located on the compressor manifold, controls air exhaustion.
Air required for leveling the vehicle is distributed from the air compressor to each air spring by nylon air lines which start at the compressor air drier and terminate at the individual air springs.
Two lines are attached to the compressor air drier.
One line runs directly to the RH front air spring.
The other line runs to the air line manifold mounted to the dash panel.
Three lines exit the manifold to supply air to the LH front, LH rear and RH rear air springs.
The compressor air drier is a common pressure manifold for both air lines so orientation of these lines at the air compressor is not required.
The compressor air drier contains a desiccant (silica gel) which dries the compressed air before delivering the air to the air springs.
During venting of any air spring, the previously dried air passes through the compressor air drier to remove moisture from the desiccant (regeneration).
Air required for compression and vent air enter and exit through a common port on the compressor head.
Vented air is also controlled by a vent solenoid valve in the compressor head.
Use of a battery charger while performing the diagnostic tests or air spring fill options is acceptable. Set a rate to maintain B+ so as not to damage the vehicle battery.
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Solenoid Valve Air Spring 
WARNING: NEVER ROTATE AN AIR SPRING SOLENOID VALVE (5311) TO THE RELEASE SLOT IN THE END CAP FITTING UNTIL ALL PRESSURIZED AIR HAS ESCAPED FROM THE SPRING TO PREVENT DAMAGE OR INJURY. The air spring solenoid valve allows air to enter and exit the air spring during leveling corrections.
The valve is electrically operated and controlled by the control module (5A919).
The valve has a two-stage pressure relief system similar to a radiator pressure cap.
An air spring solenoid retainer (5308) is first removed.
Use the active command modes on Rotunda New Generation Star (NGS) Tester 007-00500 or equivalent to vent the air spring before removing solenoid.
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Air Suspension Height Sensor
The air suspension height sensor (5359) provides a continuous voltage signal corresponding to vehicle ride height. For instance, when the sensor is fully compressed, the voltage signal sent to the vehicle dynamics control module (5A919) is 4.5 volts. When the sensor is fully extended, the voltage signal to the vehicle dynamics control module is 0.5 volt. All positions between full extension and full compression result in a voltage signal that is a linear function of position.
The air suspension height sensor sends signals to the vehicle dynamics control module through Circuits 428, 422, 424 and 427. There are three possible conditions that the control module interprets from signals from the air suspension height sensor:
NOTE: Due to electronic ride height calibration in the assembly plant, the ball stud-to-ball stud distance at trim height can vary from the following nominals. Vehicle is at trim height—192-198 mm (7.5-7.7 inches) front, 199-203 mm (7.8-7.9 inches) rear when measured from ball stud to ball stud.
Vehicle is below trim height.
Vehicle is above trim height.
The air suspension height sensor is installed and operates as follows: The air suspension height sensor is connected to the frame crossmember at one end and to the suspension at the other end.
The air suspension height sensor gets shorter when a corner of the vehicle goes down and longer when the corner of the vehicle goes up.
The four air suspension height sensors are located at the LH front, RH front, LH rear and RH rear of the vehicle. Each one of the air suspension height sensors measures the actual difference between known reference points so that the vehicle dynamics control module can respond to variations in ride height.
Variations in road surfaces are sensed by checking road wheel vertical speed and vertical travel.
If the wheel speed and travel are above a predetermined level, the shock absorbers are switched to the firm position. This reduces the chance of grounding out of the sub-frame when traveling over undulating (rough) road surfaces.
Body rolls during long, high lateral force turns (freeway exits) are also neutralized to prevent unwanted leveling actions at these times.
and more info
Control Module
A microprocessor controls the air suspension and ride control systems. The microprocessor and its support hardware are contained in the vehicle dynamics control module (5A919).
The vehicle dynamics control module also controls the amount of power steering assist. The amount of assist depends on the vehicle speed. Vehicle speed input comes from the front via the multiplex communication network. Control module output activates the power steering control valve actuator. This actuator solenoid responds to control module output to vary the hydraulic flow through the power steering short rack.
The vehicle dynamics control module responds to signals from various sensors in the vehicle to maintain the desired ride height while the vehicle is either moving or stopped. It accomplishes this by opening and closing the solenoid valves (5311). It also turns on the compressor through the compressor relay or opens the vent solenoid in response to signal inputs from the air suspension height sensors (5359).
The vehicle dynamics control module services the air suspension system and the VAPS II steering and ride control systems. The wiring harness connects to the vehicle dynamics control module using a 60-pin bolted connector.
Normally, the vehicle dynamics control module uses a 45-second averaging interval to determine when compress and vent operations are needed.
However, door switch signals' inputs can override the 45-second averaging interval so compress and vent operations can begin immediately, if needed.
There are more restrictions on vent operations than there are on compress operations: To eliminate the chance of catching a door on a curb as the vehicle vents down, the vehicle dynamics control module will not allow any venting to occur when a door is open.
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diagnosticsCHECK RIDE CONTROL Not Displayed. One or More Corners High or Low
System inactive and cannot turn on CHECK RIDE CONTROL message.
System operating correctly, ride height requires adjustment.
Air suspension height sensor popped off ball stud.
GO to Section 18-04 and retrieve DTCs.
WARNING: DO NOT ATTEMPT TO RECALIBRATE RIDE HEIGHT UNTIL THE SYSTEM PASSES ON-DEMAND SELF TEST. If On-Demand Self Test and Pneumatic Test returns SYSTEM PASSED, recalibrate ride height. Refer to Ride Height procedure as outlined under adjustments.
Drier—Air Compressor
Removal
Remove air compressor drier assembly as outlined.
Remove compressor air drier retainer clip and screw.
Remove from compressor assembly.
Installation
Check to make sure old O-ring is not in compressor assembly.
Check compressor air drier end to make sure new O-ring is in proper position.
Insert compressor air drier into compressor assembly and install retainer clip and screw.
Install air compressor drier assembly as outlined.
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Ride Height
CAUTION: This procedure is to adjust the ride height only. It should not be carried out unless a specific ride height deviation from nominal exists. Do not run this test in preparation for alignment. The accurate trim test under diagnostic test modes on the New Generation Star (NGS) Tester should be used to attain nominal ride height prior to alignment.
NOTE: This procedure should be carried out after a height sensor, vehicle dynamics control module or height sensor attachment bracket is serviced or replaced. Also, this procedure should be used in the instance of customer complaint for ride height leans and other complaints.
The ride height is adjustable using a procedure on the NGS that reprograms the vehicle dynamics control module for a different ride height. The ride height can be adjusted without adjusting the height sensor mounting brackets or the sensor ball studs.
Position vehicle on level surface.
Connect battery charger to vehicle battery.
Turn ignition switch to RUN position.
Make sure air suspension service switch is ON.
Configure NGS for 1996 Continental, Vehicle Dynamics Module.
Select Function Test selection on NGS menu.
Select Ride Height Calibration on NGS menu.
Prepare the vehicle as specified on the NGS screen.
The NGS will command the vehicle to go to its nominal ride height. While this is happening, the NGS will display "RUNNING ACCURATE TRIM TEST".
When nominal ride height has been reached, the NGS will prompt the operator to measure the wheel lip opening at each corner of the vehicle and to enter this measurement into the NGS via the thumbwheel. The nominal wheel lip opening (635 mm front, 616 mm rear) will be displayed until a different number is entered by the operator. No adjustment will occur if nominal values are entered.
Measure and enter each wheel lip opening. Select each corner by pressing the trigger button. Press DONE when all four corner wheel lip openings are measured and entered.
The NGS will first display DOWNLOADING CALIBRATION, followed by RUNNING ACCURATE TRIM, followed by CALIBRATION COMPLETE. When the calibration is complete, measure the wheel lip openings to verify that they are close to the nominal (see diagram).
The vehicle dynamics module limits the magnitude of ride height adjustments that can be made electronically via the NGS. If the proper wheel lip openings are not attainable by running this procedure, the height sensor ball studs will require adjustment to attain the desired wheel lip opening. Lowering the ball stud will raise the front and lower the rear vehicle ride height and raising the ball stud will lower the front and raise the rear.
After making this ball stud adjustment, rerun the Ride Height Calibration procedure with the NGS to fine tune the adjustment.
Final comment
You may need to have a dealer use his NGS equipment to cehck rie height adjustment. You can't do it without it. SHould charge about one hour to do this.
Are you getting a fault displayed on your message center?
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WARNING: NEVER ROTATE AN AIR SPRING SOLENOID VALVE (5311) TO THE RELEASE SLOT IN THE END CAP FITTING UNTIL ALL PRESSURIZED AIR HAS ESCAPED FROM THE SPRING TO PREVENT DAMAGE OR INJURY. 
no purge valve, I tried to spray the lines from the dryer and the dryer base to find the lead but no leak was present. I have 2 lines on top of the dryer I assume one is for the front and one for the back. front came up as soon as I turned the system back on but the back never tried to come up at all. I say no purge valve, it only has the opening at the base and for the two lines comeing out at the top.
do you have any electrical connections going to the dryer? if so there is a purge valve.
does your dryer have a purge valve? if so check to see if it is stuck open, the air pressure build up is probably so low you can not hear it leaking, but you should be able to feel it, again this procedure is only if you have a purge valve
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