Member Since: 03 Mar 2019
Location: Tasmania
Posts: 148
Recommended Hitachi Air Supply Unit (compressor) maintenance
Both our MY12 D4's have the Hitachi Air Supply Units (compressors) fitted. Is there any recommended maintenance or servicing of these to prolong their lives? Most of the discussions from my searching really only start once faults are already occuring. It seems that some has had issues with the desiccant in the Air Dryer going off or turning to powder? Then I've read other stories about people who've done repairs on them to find that they only lasted another month or so.Mine - modified MY03 LT L318 Discovery 2a HSE Td5 15P
Hers - MY12 L319 Discovery 4 Lion 2.7L TDV6
Dads - MY98 LJ Discovery ES 3.9L V8
5th Jan 2021 2:37 am
garrycol
Member Since: 06 Dec 2010
Location: Canberra
Posts: 1115
Why would your D4s have the Hitachi - from the factory they would have been AMK so it seems odd to have replaced them with a Hitachi at some stage. The change was late 2010 into 2011 so your vehicles should have had the AMK - so double check what you have. (see my comments at the bottom and in your other post)
To your question though - not real day to day maintenance required - take the bottom cover off after being offroad and wash out all the dirt as it can cause overheating.
Your first indication of a pending issue will be an occassional C1A20 fault code where the tank (gallery) fills slowly. This is because the desiccant is failing and the filters clogged.
Also consider getting a replacement exhaust valve and housing. Here is just the valve but also get a housing as they can be damaged undoing them - they are hard to find but are listed on ebay
https://www.ebay.com.au/itm/Land-Rover-Dis...ctupt=true
Also learn how the system works as it simplifies its understanding an maintenance.
Basically air is taken into the compressor and goes through the desiccant and is dehumidified - moisture stays in the desiccant. Air then goes through the central valve block to the tank (there is only one pipe in and out of the tank) and is controlled by the central valve block.
When required air is released from the tank to the central valve block (controlled by the central valve block) and then directed to the front or rear or both as required where the dehumidified air goes to the airbags (controlled by the front or rear valve block).
When air is the be released from the airbags, front or rear valve blocks open and the air goes to the central valve block which opens and sends the air back to the desiccant chamber in the air compressor - this releasing air is dehumidified air and as it goes back through the desiccant it takes water out of the desiccant and exists the compressor at the rear through the exhaust valve and via a pipe to the rear drivers side corner of the car where it vents to atmosphere via a small silencer. Controlling this is the suspension ECU and the height sensors etc.
Garry
PS READ IN CONJUNCTION TO MY REPLY TO YOUR RELATED POST - DEFINITELY A HITACHI
5th Jan 2021 3:12 am
twr7cx
Member Since: 03 Mar 2019
Location: Tasmania
Posts: 148
They're 2012 complied in Australia. Both are built late 2011 as MY12 models so likely last of the Hitachi units thrown into them before the changeover. Perhaps being the cheaper base TDV6 models they were more likely to get the old parts too? Hitachi units are definitely listed in the Land Rover Microcat parts catalogue too for D4s.
Is the replacement exhaust valve and housing you linked the same as:
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