[Arnie65]

if you bridge the compressor relay (remove the relay, there is usually a diagram on the relay identifying the pins on the relay, and place a piece of wire between the two relevant contacts - those that feed 12V to the compressor), then if the compressor runs, it will point to a faulty relay or lack of signal to the relay. If the compressor does not run, then double-check the fuses, as it indicates an absence of power.

 

[Arnie65]

In this relay, Pin 30 is the 12V supply and Pins 87 are the output to the compressor.

Remove the relay and place a copper wire into the relay socket connector bridging Pins 30 and 87

As said above If the compressor runs, you have a faulty relay or lack of signal to relay.

If the compressor does not run you do not have a main power feed (pin 30) at the relay, or a wiring fault between pins 87 on the relay socket and the compressor, or a lack of earth/ ground at the compressor.)

It would help to have mutimeter (~£10 for a basic one at Halfords, Amazon etc), then you could measure the voltage at pin 30 (on relay socket) and test the relay coil (pins 85 and 86 on the relay), as well as check the ground connection.

 

[Arnie65]

If bridging the relay terminals (on the relay socket) does not work, it would be an idication that either the 12V supply (terminal 30) is not working or that the compressor motor doe not have good ground.

This is where a multimeter would be useful.

Normally, it would be a straight connection from the battery through the fuse to terminal-30 on the relay. If this is the issue, check the fuses carefully and make sure you have located the right one.

I would not add another 12V supply, but try to find the problem with the existing one.

 

[Arnie65]

I do have a multimeter and will try to use that as you suggest but I’m a novice on this stuff! I’ll do some reading up.

I really appreciate your help.

To check the relay coil, set the multimeter to read resistance (Ohms) and check the reading between pins 85 and 86 on the relay, which are the coil connections. You should probably see around 20 - 30 Ohms, If you read kilo-Ohms or more, the coil is probably faulty. However, this would be unlikely with a new relay. Alternatively, Apply 12V between 85 and 86 and listen if you can hear it click.

If you are sure you have checked the relevant fuses and replaced the relevant relay, I am guessing that you will find that its is the car's control system that signals the relay (applies voltage to 85 and 85) that is faulty. So, I would go the diagnostic route suggested by Johnny, if the relay checks out OK and you have 12V at terminal 30 on the relay socket.

(I only know about these air pumps from a Mercedes perspective, but on that system, if the car battery is low, the pump's control system locks-up and the pump continues to run to the point where either the fuse or the pump or both burn out from over-running and over-heating. )

 

[Arnie65]

You can test their coils to see if the resistance looks about right (probably around 10 Ohms) and not open circuit or a high value. But this won't tell you if the valve is stuck or corroded, just whether the coil is good.

 

[Arnie65]

I know that, should the compressor fail in an MB, you can wedge some chocks into the suspension frame to keep driving. maybe there's a simialr method for yor car so that you can drive it to a workshop, as i think this will be more effective than a mobile mechanic.

If you have two working solenoid valves, can you not swap out your old valves with the new ones ?

The air suspension system use a number of sensors to detemine when and if to run the compressor, these include potentiometers on drop-links that inform the ride height. You really need a diagnostic scanner to find the reported fault codes. Otherwise, it's just guess work,

 

[Arnie65]

If you have a spare old laptop (not too old, though), you can install INPA for free, albeit with a bit of effort to set it all up. You then just need the OBD socket adapter.