It looks like one is the air inlet and the other is an air exhaust line.I have a random question after replacing my compressor.
There are three ports on the compressor. The inlet port which runs up behind the drive's tail light. The outlet port, which runs to the center valve block. And lastly, the third port which comes off of what I presume to be the drier on the compressor and runs to somewhere up in the vehicle.
What is this third port coming off the drier for. Some kind of pressure equalization vent or something?
I've pretty much done it all to my suspension. I had the Hitachi compressor originally installed, but it died in 2019, so I replaced it with the AMK at the time. I was told it would last longer and would run a lot cooler than the Hitachi, but I honestly can't confirm that for fact. At the end of the day, they both worked fine. In my Hitachi's defense, I had a bad air strut and valve block at the same time...and that pretty much killed it.
Just so you know, the air lines are slightly different between the different compressors. (AMK vs. Hitachi...I don't know much about the Arnott version.) When I installed my AMK, it came with a conversion kit as part of the assembly. I also came with upper and lower cowlings because they are also slightly different as well. When I swapped mine I just unbolted the entire compressor bracket, and I'm not gonna lie, there's one bolt in the back that I could only get to with an open ended wrench and 1/4 turn at a time.....it was painful....getting it back in was even tougher....I want to say I unbolted the compressor from the bracket and was able to pivot it out of the way to get the bolt threaded. Sorry, it's been a while since I've done it.
As for new vs. rebuilding, I have replaced my front valve block 3 times, and it has recently failed again. I'm trying the re-seal route this time because everywhere I looked they were not in stock. (FYI, I was just looking last week). Also, because a $20 repair sounds a HECK of a lot better than a $200 one. Honestly, I think the seal may work, but I'll let you know when I get it back in the truck tomorrow. I did notice one thing, and that's the fact that it appeared one of the halves of my valve block was slightly warped. I should have taken a picture yesterday. Normally, the leaks are internal, but in my case I believe the mating surfaces between the 2 halves of the unit aren't true.....I know, this is your shocked face. Although, I now find myself wondering it the standard, "it's an internal issues with these valve blocks" is actually true. If the re-seal doesn't work, I am going to try and drill some additional holes through the 2 halves to run 2 or 3 additional screws for extra flattening force. I'll let you all know how it goes. I figure if it's already broke, I can't make it any worse! LOL!
Typically I'd say replace the blocks and go with new, but I'm on my 4th front block, which I'm now trying to fix....so new or old, it sounds like there's an issue with the quality of the parts they're putting out.
Almost forgot, this seems to be a good site that sells a lot of the repair parts you might want:
Air Suspension Repair Kit and Parts for Land Rover, Range Rover, 4x4 Air Seals - mail order availableWe manufacture and supply Air suspension repair kit in the UK to fit Land Rover, Range Rover, Audi, BMW, Mercedes-Benz, Jaguar, Porsche, and Volkswagen 4x4.4x4airseals.com