How the Rear Air Suspension works

[RF Overlord]

This is courtesy of the Lincolns Online tech forum:

HOW THE AIR SUSPENSION WORKS

The system consists of:

A compressor with built in vent solenoid and air drier
Compressor relay
Two air springs and spring solenoids
A height sensor
An on/off switch and a control module

The control module also receives inputs from the courtesy light switches and vehicle speed sensor. If the speed sensor isn't working then the air suspension will not function correctly.

When the car is started the air suspension module will immediately raise the vehicle to trim height if needed. No venting is allowed for 45 seconds after starting, so if the vehicle is high it will remain high for at least 45 seconds. Venting is also not allowed when a door is open. When the car is moving the module uses a 45 second averaging procedure to control trim height. This means that unless the module receives a high or low signal continuously for 45 seconds no adjustments are made. If the car 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.

[MileHiMarauder]

Good afternoon Overlord. A little help if possible. I noted a droop in my right rear, so I have replaced both air springs and figured might as well do the compressor too. Now she is back together and I am still getting the air suspension light on the dash and no activity from the compressor (still sitting low). I have checked two fuses and replaced the relay. I have looked at the height sensor and find both ends attached. I have ordered a new one and await arrival. You mention a control module and I have no idea what or where it is. Can you elaborate please. All was working before I got the air suspension light which I assume was due to the deteriorated air springs. Is there a “reset” somewhere? Appreciate ant clue(s) you may be able to provide. Thank in advance..

[Turbov6Bryan]

The air ride module is located behind the glovebox.

I would check the new compressor for power and ground, then bench test it

Make sure the sensor is attached at the drivers side rear axle

[RF Overlord]

Check the switch in the trunk, also.

[Marvbearcat1]

Hello. I replaced my air suspension compressor and air bags and the air compressor is not coming on. Any suggestions on to why this is happening? Needing to fix ASAP.

[fastblackmerc]

Hello. I replaced my air suspension compressor and air bags and the air compressor is not coming on. Any suggestions on to why this is happening? Needing to fix ASAP.

Need to check what Overlord said to.

[InglewoodAwk]

Left side does not lift the car. Enough pressure goes into the bag so that it is not empty but it definitely stops filling well before the right side. The right side seems to compensate for the left so it seems high. I had a broken line/connection and audiable hiss going to the left side last fall. Compressor would run until i got the light. I had changed out the left bag, solenoid and o-ring before I found out what was actually wrong. That was repair was done by Aamco. This past spring, the car started to droop on the left side again. Swapped out bags, solenoids and o-rings back and fourth between Aeronot and Motorcraft with no change and swapped all of that between left and right with no change. Can “trick” it into raising the left side by letting both sides fill, deflating the right sided, reconnecting and letting it fill until they become even. Takes about a week to droop all the way down. Car bottoms out and the ride is horrible. 2004 with 104k miles. Local mechanic and I are stumped.

[RF Overlord]

Possibly you have a binding shock or control arm or a crimped/clogged air line to the left side.

[jmsa540]

Left side does not lift the car. Enough pressure goes into the bag so that it is not empty but it definitely stops filling well before the right side. The right side seems to compensate for the left so it seems high. I had a broken line/connection and audiable hiss going to the left side last fall. Compressor would run until i got the light. I had changed out the left bag, solenoid and o-ring before I found out what was actually wrong. That was repair was done by Aamco. This past spring, the car started to droop on the left side again. Swapped out bags, solenoids and o-rings back and fourth between Aeronot and Motorcraft with no change and swapped all of that between left and right with no change. Can “trick” it into raising the left side by letting both sides fill, deflating the right sided, reconnecting and letting it fill until they become even. Takes about a week to droop all the way down. Car bottoms out and the ride is horrible. 2004 with 104k miles. Local mechanic and I are stumped.

I'm kind of experiencing the same problem. What's the stock height that both sides need to be at?

What's a sign of shot air springs? Just straight out low as all get out?

[Turbov6Bryan]

I'm kind of experiencing the same problem. What's the stock height that both sides need to be at?

What's a sign of shot air springs? Just straight out low as all get out?

typically a front spring will show the car leaning to one end worse in the back, since the front is lower.
Grab a tape and flat flat flat concrete, not the garage, its tapered.

[justbob]

typically a front spring will show the car leaning to one end worse in the back, since the front is lower.

Grab a tape and flat flat flat concrete, not the garage, its tapered.

I’ve yet to measure an identical reading side to side. Maybe on a frame jig LOL

There will always be slight differences car to car, corner to corner.


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[boom boom]

Does anyone know the approximate air pressure at curb weight and ride height? I know that the pressure value is always changing (based on vehicle weight) and that everything is based on the ride height sensor; however, I have a special application and I need to know a baseline for the compressor. Even if it's just the compressor spec for the max pressure output, that would be great. Look for a thread from me later as this project moves along.

[daniel.drives]

If you're looking for stock ride height, mine was 29 inches plus or minus an eighth as measured from the rear fender arch to the ground, directly in front of the wheel center.

Boomboom, Assuming a bag diameter of 7 inches (I'm too lazy to hop under and measure the circumference but that would give a more accurate number) the area of one bag is about 38.5 sqin, assuming each corner is holding 1/4 of the 4000 lb car, that would indicate an air pressure of 26psi. No idea what the max of the compressor is.