dRock's RAS FAQ

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Just some quick tidbits on the 92+ panther (90-91 TC as well) RAS system, for those who arecurious.

The panther RAS system was, and continues to be one of the smoothest and well engineered of its kind.

• The system consists of two rear air springs; manufactured by Firestone, a compressor and drier assembly; made by Tokico, two air solenoids, mounted atop the air-springs, and a height level sensor with ride height computer with trunk-mounted system deactivation switch.
• Per the late, great Ned Nuss - The Town car has always used a Firestone spring. During the development process for the 1990 Town Car it was found a Bridgestone sleeve gave better ride quality and enhanced durability.
  • When launched on the 1990 Town Car the springs used Bridgestone sleeves purchased by Firestone until they could manufacture the sleeves themselves.
• Contrary to popular belief, the system does not use air-shocks - rather, traditional gas pressurized shock absorbers are used.
• Generally, the RAS system is very robust normally surpassing well over 100 thousand miles before major system failures.
• The module strategy runs the compressor every time the engine is started and it runs for 10 seconds or so or until the ride height sensor is within range. When driving, the module counts the number of times the sensor sees the high side of the trim band and the low side over 45 seconds. The compressor or vent solenoid is then triggered to put the rear ride height roughly in the middle of the trim band. The air spring solenoids are opened when ever the compressor or vent solenoid engage.
• After the vehicle is parked, engine off and all doors are closed - the system will vent some. This is normal operation and should not be of any concern
  • Up to one hour after the vehicle has been parked, the compressor can come on to level to trim height. ON some models, the using the keypad can reset this one hour period as well.
• The air spring's air solenoids only open during compress & vent operations.
  • Both airsprings are fed via a single air line from the compressor.
  • Air pressure is equalized between both bags whenever the vent solenoids are open (as there is only one air line that is t-ed of to each spring)
  • There is no way for the RAS to inflate/deflate only one airspring at a time (Barring a leaky airbag or a pinched section of the short section of air hose that is teed-off from the main hose that supplies one air bag)
  
  
  
• The compressor/drier is mounted below the engine air cleaner
• The ride height computer, which is integrated to the Electronic-Variable-Oriface (EVO) speed-sensitive steering module mounted behind the glove box, uses input from the height sensor to determine how much to run the compressor, or vent the air springs.
  • That said, there are no air pressure sensors used anywhere in the RAS system. Air pressure will vary as needed to maintain ride height based from the sensor.
• The system only levels the car front to rear, not side to side.
• On -97 vehicles, the height sensor is located on the Upper LH rear control arm. On 98+, it is on the watts linkage. The height sensor provides a hall-effect signal to the RAS/EVO module.
  
  
• The RAS module/ride height computer also uses inputs from the door switches and VSS (-03, -97 Town Car).
  • If the VSS is not operating correctly then the RAS will not function correctly.
• When the ignition is turned to run from off, the RAS will immediately raise the vehicle to trim height.
• THe RAS will not vent for 45 seconds after off-->run ignition cycle.
• THe RAS will not vent when a door is open.
• If the vehicle is stopped and a door is opened and closed an immediate trim height adjustment will be made.
  
  
• If during a lowering or raising procedure trim height cannot be achieved in the "time out" period, the "Check Suspension" light will illuminate and the air suspension module will turn off.
• When the ignition is turned off and back on the air suspension module will return to normal operation and try to maintain trim height.
• The "Check Suspension" light is also illuminated when the air suspension is switched off using the on/off switch.
• After switching the car off the air suspension remains active for one hour.
  • From 0 - 59 minutes only venting is allowed providing all doors are closed.
  • At 60 minutes, if trim height is low, the module will raise the car to trim height or run the compressor for 23 seconds if this is not achieved.
  • At 61 minutes the air suspension system is switched off.

• Dual Action System
  
  WARNING: BEFORE SERVICING ANY AIR SUSPENSION COMPONENTS, DISCONNECT POWER TO THE SYSTEM BY TURNING AIR SUSPENSION SWITCH OFF OR BY DISCONNECTING BATTERY GROUND CABLE TO PREVENT VEHICLE DAMAGE OR PERSONAL INJURY.
  
  
  
  • The rear air suspension:
    • is an air-operated, microprocessor-controlled, suspension system.
    • replaces the conventional rear coil spring suspension.
    • provides low spring rates for improved ride and automatic rear load leveling.
    • is standard equipment on Town Car.
    • is available as an option on Crown Victoria and Grand Marquis.
    
    
    
  • The rear air suspension system has the following features:
    • The system is operational with the ignition switch in the RUN position.
    • Automatic rear load leveling has limited operation for one hour after ignition switch is turned to OFF.
    • The air suspension switch, located on the RH side of the luggage compartment, must be turned OFF when the vehicle is on a hoist, being towed or jump started.
    • The CHECK AIR SUSPENSION warning indicator is located in the instrument cluster, to the right of the speedometer.
    • -- The warning indicator flashes five times and then stays on with ignition switch in the RUN position and the air suspension service switch turned off or when a system malfunction is detected.
    • -The rear leveling system operates by adding or releasing air in the springs to maintain the level of the vehicle at a predetermined rear suspension ride height dimension, and is controlled by a control module (5A919). (Refer to «Adjustments».)
    • -The rear air suspension control module also controls the electronic variable orifice (EVO) power steering. Refer to «Section 11-02» for Description and Operation of the EVO power steering system.
    • -Air required for leveling the vehicle is distributed from the air compressor to the rear air springs by a nylon air line which runs from the compressor air drier (5346) through a Y-fitting to each individual air spring.
    
    
    
  
  
  
  
• Weight Added
  
  • When weight is added to the vehicle the air suspension system responds as follows:
    • The air suspension height sensor length is reduced from trim length, sending a "rear is low" signal to the control module (5A919)
    • The control module then turns the compressor on by grounding the compressor relay control Circuit 420 (DB/Y). This restores the rear of the vehicle to trim position.
    • B+ is supplied to the relay coil by Circuit 1053 (LB/PK) (Crown Victoria, Grand Marquis) or 414 (O/R) (Town Car).
    • The control module opens the spring solenoid valves (5311) by switching Circuits 1114 (BR/PK) and 1115 (T/W) to ground. This allows pressurized air to enter the rear air springs.
    • B+ is supplied to the air spring solenoid valves by Circuit 1053 (LB/PK) (Crown Victoria, Grand Marquis) or 414 (O/R) (Town Car).
    • Compressed air flows from the compressor through the compressor air drier air lines and spring solenoid valves into the rear springs (5560).
    • As the rear springs raise the rear body height, the air suspension height sensor (5359) increases in length until the preset trim height is reached.
    • The control module then turns off the compressor (through the relay) and closes the air spring solenoid valves.
  
  
  
• Weight Removed
  
  • When weight is removed:
    • The air suspension height sensor length is increased from the trim length, sending a "rear is high" signal to the control module (5A919).
    • The control module then opens the vent solenoid valve (located in the compressor assembly) by switching Circuit 421 (PK) to ground and opens the solenoid valves (5311) by switching Circuits 1114 (BK/PK) and 1115 (T/W) to ground. This restores the rear of the vehicle to trim position.
    • Compressed air flows from rear springs (5560), through the air spring solenoid valves, air lines, compressor air drier (5346), and out the vent solenoid valve.
    • As the body lowers, the air suspension height sensor length decreases until the preset trim height is reached.
    • The control module then closes the vent and solenoid valves.
  
  
  
  
• Control Module Power and Ground
  
  
  • The control module (5A919) has the following features:
    • Power is provided by Circuit 1053 (LB/PK) (Crown Victoria, Grand Marquis) or 414 (O/R) (Town Car). (1996 - other year ranges will/may have different colors)
    • The air suspension switch is powered through Circuit 429 (PK/LG). (1996 - other year ranges will/may have different colors)
    • Control module ground is provided through control module wire harness Pin 6, to the RH inner quarter panel sheet metal, near the control module. (1995-2002)
  
  
  
  
• Ignition Switch Input
  
  
  • System responds to ignition switch input as follows:
    
    • The control module (5A919) stays powered for one hour after the ignition switch is turned to the OFF position in order to perform leveling corrections after occupants and luggage are removed from the vehicle.
    • When the ignition switch is turned to RUN, Circuit 298 (P/O) is supplied B+. (1996 - other year ranges will have different colors)
    • If there is an open in Circuit 1053 (LB/PK) in or its feed circuits, the control module will be inoperative and diagnostics cannot be entered. (1996 - other year ranges will/may have different colors)
  
  
  
  
• Door Courtesy Lamp Switch Input
  
  
  • System responds to lamp switch (13713) as follows:
    • The control module (5A919) uses the door courtesy lamp switch input for two different functions:
    • -- preventing vents when a door is open to avoid the possibility of the vehicle lowering and the door catching on an obstruction.
    • -- servicing a correction immediately, if needed.
    • -The control module cannot sense which doors are open, only that one or more doors are open, or all doors are closed.
    • -If a damaged door lamp switch (always open) or a short to battery in Circuit 344 (BK/Y)(1996 - other year ranges will have different colors) exists, the control module will interpret that a door is open and not vent unless vehicle speed is above 24 km/h (15 mph).
    • -- Above 24 km/h (15 mph) the control module disregards all door signals.
  
  
  
  
• Air Compressor Assembly
  
  Note: The compressor motor contains a thermal overload circuit breaker. The circuit breaker automatically resets if tripped by excessive heat.
  
  Note: The compressor air drier (5346) may be serviced separately.
  
  
  • The air compressor assembly:
    • -consists of the compressor and vent solenoid; neither is serviceable.
    • -is mounted in the engine compartment on the LH fender apron below the engine air cleaner (ACL) (9600).
    • -is a single-cylinder electric motor-driven unit which provides pressurized air as required.
    • -is powered by a relay, controlled by the control module (5A919).
    • -passes pressurized air through the compressor air drier which contains silica gel (a drying agent).
    • -moisture is then removed from the compressor air drier when vented air passes out of the system during vent operation.
  
  
  
• Compressor Air Drier Assembly
  
  
  Pitcure of a removed compressor:
  
  The picture above shows a Town Car compressor with the airline connection circled in red and the vent solenoid circled in green.
  Courtesy Lincolns online
  
  
  
• Compressor Relay
  
  
  • The air suspension compressor relay and bracket (9C392) is needed because the control module cannot directly provide the high current needed to run the compressor motor. It operates as follows:
    • -The control module (5A919) grounds Circuit 420 (DB/Y) to energize the relay coil. (1996 - other year ranges will have different colors)
    • -When energized, the coil creates a magnetic field which closes the relay contacts, connecting Circuit 1053 (LB/PK) to Circuit 538 (GY/R) for Crown Victoria, Grand Marquis or 414 (P/O) for Town Car.
    • -High current then flows from battery to the compressor motor.
  
  
  
  
• Air Spring Assembly
  
  • Two air springs:
    • -replace the conventional coil springs.
    • -support the vehicle load at the rear wheels (1007).
    • -are mounted between the axle spring seats and the frame upper spring seats, similar to the conventional rear coil spring system.
  
  
  
  
  Acutal spring pic:
  
  
  
  
• Solenoid Valve, Vent
  
  CAUTION: The vent solenoid valve has an internal diode for electrical noise suppression and therefore is polarity sensitive. Care must be taken not to switch the battery feed and ground circuits, or component damage will result.
  
  
  • The vent solenoid valve:
    • -allows air to escape from the system during venting corrections.
    • -is located above the air compressor cylinder head.
    • -is enclosed in the cylinder head casting, which forms an integral valve housing that allows the valve tip to enter the pressurized side of the system.
    • -has an O-ring seal which prevents air leakage past the valve tip.
    • -opens when the rear is high and the control module (5A919) determines lowering is required.
    • -provides an escape route for pressurized air when opened.
    • -the vehicle will not lower unless the air spring solenoid valves (5311) are also opened to allow air to leave the springs.
    • -air is exhausted from the springs and vented through the compressor air drier.
    • -is not a serviceable item.
  
  
  Pitcure of a vent solenoid:
  
  Courtesy Lincolns online
  
  
  
• Solenoid Valve, Air Spring
  
  WARNING: NEVER ROTATE AN AIR SPRING SOLENOID VALVE 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 (5311):
    • -allows air to enter and exit the air spring during leveling operations.
    • -is electrically operated and controlled by the control module (5A919).
    • -Because the spring solenoid valves are airtight, connecting air lines are not required to be completely airtight. The air lines only contain pressurized air during vent and compress operations.
  
  
  
  
  View of an actual solenoid:
  
  Courtesy Lincolns online
  
  
  
• Air Suspension Service Switch
  
  WARNING: THE AIR SUSPENSION SWITCH MUST BE TURNED TO THE OFF POSITION WHEN THE VEHICLE IS HOISTED, JACKED, TOWED, JUMP STARTED OR RAISED OFF THE GROUND TO AVOID UNNECESSARY OPERATION OF THE SYSTEM AND/OR POSSIBLE DAMAGE TO ITS COMPONENTS.
  
  
  • The air suspension switch provides a signal to the control module (5A919) in the ON position only. The switch is located on the RH side of the luggage compartment.
  
  
  
  
• Control Valve Actuator, Power Steering
  • The power steering control valve actuator (3783) is located on the steering pump below the engine on the LH side.
  • The power steering control valve actuator generates a differential pressure, dependent on flow and current input.
  • -This differential pressure is used to control the spool valve in the CIII power steering pump.
  • -The power steering control valve actuator/spool valve regulates the hydraulic flow and when combined with a current controlling device, yields a variable assist power steering pump (3A674).

Air Suspension Height Sensor

• The air suspension height sensor (5359) sends signals to the control module (5A919) through Circuits 427 (PK/BK) and 428 (O/BK) (1996 - other year ranges will have different colors) . There are three possible conditions that the control module interprets from signals from the air suspension height sensor:
  • Vehicle is at trim height.
  • Vehicle is below trim height.
  • Vehicle is above trim height.
  
  
  
• The air suspension height sensor is installed and operates as follows:
  • -Is connected to the frame cross member at one end and at the LH rear upper arm at the other end.
  • -The air suspension height sensor gets shorter when the rear of the vehicle lowers and longer when the rear of the vehicle rises.
  • -Magnets mounted in the lower slide portion of the air suspension height sensor move relative to the air suspension height sensor housing.
  • -This movement generates a signal that is sent to the control module through two small Hall effect switches attached to the air suspension height sensor housing.
  
  
  
• The signal generated by movement of the magnets determines switch opening and closing as follows:
  • At trim height, the switches remain closed and the control module receives a trim signal.
  • Upward movement of the magnets will open one switch to indicate a high condition.
  • Downward movement of the magnets will open the other switch to indicate a low condition.

Control Module

• The rear air suspension/EVO control module (5A919) services both the rear air suspension system and the EVO steering system.
  • -The wiring harness connects to the control module using two separate push button release connectors.
  • -The connectors are keyed so that they cannot be installed incorrectly.
  
  
  
• Control module operates as follows:
  • -In general the control module uses a 45-second averaging interval to determine when compress and vent operations are needed.
  • -However, door lamp switch (13713) inputs can override the 45-second averaging interval so compress and vent operations can begin immediately, if needed.
  • -The 45-second averaging interval is used to keep the control module from making unneeded corrections.
  • -When a vehicle at the correct rear trim height hits a bump, the air suspension height sensor output will read low and high in addition to trim until the oscillations die out.
  • -If the control module was to correct for these "bump induced readings", system duty cycle would increase unnecessarily.
  • -The 45-second averaging interval not only eliminates corrections due to bumps, but also eliminates unneeded corrections resulting from braking, accelerating, and turning. The control module tabulates the air suspension height sensor readings, and does not begin a compress or vent operation until the air suspension height sensor (5359) reads low or high for 45 seconds nearly consistently.
  • -Vent operations are more restricted with the ignition switch in run. Compress operations are more restricted after the ignition switch is turned OFF.
  • -To eliminate the chance of catching a door on a curb as the vehicle vents down, the control module will not allow any venting to occur when a door is open.
  • -The control module does not allow any vent operations for the first 45 seconds after the ignition switch has been turned to RUN.
  • ----Even if a vehicle is extremely high in the rear, DO NOT expect it to vent until the ignition switch has been turned to RUN for 45 seconds.

Here is a picture of all the RAS components, excluding the computer and switch:

Pictured is a 90-97 Town Car system, all are similar, however.
The air springs pictured are base rate. The upper part where the hose connection is located is the cap. The tapered cylinder at the bottom is the piston. It is plastic and rests atop the axle's spring pearch.

A brand-new Firestone 98+ base RAS sir-spring:

The label:

Pair of 98+ base-rate airsprings at operating position

THe piston (what rests atop axle spring perch), base-rate:

The cap & solenoid:

A 90-97 base label:

98-02 height-sensor:

Courtesy http://www.crownvic.net/liquid
03+ Height sensor:

---Courtesy sid210sa

For info on adjusting the RAS ride height, check this link:
http://s95318876.onlinehome.us/liquid/index.html
Note, 03+ owners have commented that the sensor must be moved the opposite of the 98-02 directions.


Rates:

• The air-springs rate is determined by the piston design. Each panther air spring is color coded, using the upper cap and the plastic piston.
• THe rates and color codes go as follows:
  
  

  -1997 Base RAS	Cream piston and cream cap	75 lbs/inch
  all years HPP air-springs	black piston and cream cap	102 lbs/inch
  1998+ Base RAS	cream piston and black cap	89 lbs/inch

  
  
  
• Keep in mind air-springs are variable rate, those ratings are with static load.
• For comparison, the steel rear coil rates are: 130 lbs/in civilian, 160 lbs/in CVPI.
  
  
• You can easily see yours by going under the rear of the car (no need to raise it) on the bottom of the Air-Spring is the plastic support that rests on the perch (the piston). Cream/white indicates it is the low-rate spring, as used in non-HPP RAS equipped panthers (Town Cars included)
• The black piston-ed air-springs are for HPPs, also used on Marauders and Town Car touring sedans and 99+ Limos/Livery.
• Cream piston for base RAS equipped non-HPP (or similar) models, towing package included. LX Sports also use base rate air springs, the reason behind this is the 17" wheels. Ford had to provide some give in the suspension to offset the lower profile tires. Marauders have the 18" wheels, and no-compromises on the HPP, MMs also ride like trucks IMO lol
• Sport owners will also find they do not have the 21mm HPP/MM sway bar, rather the smaller 17mm.
  • Kinda unfair, as Ford advertises the LX Sport as having the HPP, but in fact an LX Sport's rear suspension is the same as a normal 98+ Town Car.

Swapping:

• The air springs will swap between all applications, the ride height computer/height sensor and drier are the same between packages as well.
• A panther owner with base-RAS can simply swap the rear air springs in favor of HPP air springs and enjoy HPP RAS.
• Arnott Industries has recently begun manufacture of aftermarket 'Limo' rear air-springs. These aftermarket units have an aluminum piston, instead of the plastic. They are still HPP/Limo/MM rate, however.
  • Arnott also manufactures direct replacement aftermarket air suspension parts for panther RAS, at significantly lower cost than Ford.
  
  
  
• A factory RAS system is not easily retrofitted into a non-RAS panther, but can be done.
• Steel coils can be swapped in place of the air-springs, you will also need the insulators. The RAS is a very nifty feature, IMO, it would be a shame to get rid of it over minor complications. It is very durable, and often will last the life of the vehicle.

This article was meant to provide an understanding of just how the panther RAS system works.
For system repair and diagnosis, please refer to this link: http://www.lincolnsonline.com/tech/00061.html

 

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Email me at dRock96Marquis@crownvic.net

 
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Page last updated: 3-07-2007