LS400 MK3 Aircon Compressor Replacement

Razor61 · June 15, 2020

A few weeks ago my aircon stopped working with the AC light flashing. The Air Conditioning isn't an area I know a lot about at all so contacted a mobile Aircon Specialist to have a look. After a few checks it looked like the compressor at fault, either the compressor itself or the magnetic clutch assy. 12v was being applied to the clutch but clutch wasn't engaging so it wasn’t the aircon relay at fault (I presume). So system de gassed and we agreed that I would purchase a new compressor, fit it and then he will re gas the system. I also received some tips/information on what to do while replacing the compressor.
New Denso compressor and drier kit purchased from RockAuto Friday afternoon and it arrived the following Monday afternoon, pretty good service. I replaced the compressor on Saturday and I'm waiting for it to be re gassed next week. I thought I'd post some information on how I did it and what bits I needed to remove in order to remove the compressor which may be useful for anyone else that needs to do it or is thinking of doing it. I may have forgot a few details so don't take this as 'gospel' but the basics are there. It took me 4-5 hours to do but I took my time and replaced the drier as well. If I had to do it again it would be 2 hours max.
I knew the V belt had to be removed so started with that, removed smallish Battery cover, air cleaner inlet and fan with viscous coupling. So it then looked like this.

Disconnected the aircon lines to the compressor, placed a rubber glove round each one and wrapped insulation tape round to seal as best I could to stop any moisture entering the system. Used some cable ties to hold the pipes out of the way. Disconnected the aircon electrical connector.
Jacked up the car at the passenger side and removed the under tray so I could then get to the compressor from underneath. One quick look told me the compressor has to be removed from the top. I'd already removed the fan assy but I needed to remove the fan cowling as well. 4 x bolts (2 x at the bottom and 2 at the top with captive square nuts) rh one at the top and the 2 x bottom bolts were rusted so plenty of plus gas and left for a while then removed them relatively ok.
Had a good look for the 3 x compressor mounting bolts, there are a quite a lot of wires and pipes around this area plus a lot of dirt that will end up on your face and in your eyes while doing the job so wear some glasses or goggles at the very least. Make sure you locate the correct bolts by having a good look at the new compressor as you could easily start undoing the wrong stuff like the oil filter housing/pump. LH bottom bolt is easy to see and remove, LH top is relatively easy but not a lot of room, the RH one at the back isn't easy to see so you need a light to shine round and get to it with a long extension. I removed the plastic engine under cover as well (shown below and be careful of rusted bolts for this as well…………) to give me better access to the RH bolt.

Un clipped the fastener for the aircon electrical connector cable which is attached to the compressor. Removed the 3 x bolts, bottom 2 are the same size and the LH top bolt is longer. You will need to work out how to do this yourself with ratchet/extension etc. There are some brackets that are attached with the bolts so take note of these. Wiggled the compressor forward and rested it on the roll bar then removed it carefully from the top between the front of the engine and radiator.

Installed the new compressor (see next section about the compressor itself), bolted in place and torqued the bolts to 49nm. Re fitted the aircon line connectors and torqued down the nuts to 10nm after thoroughly cleaning (super clean as best I could), fitting new 'o' rings with a smear of compressor oil, smearing some compressor oil in the compressor connector 'holes'. Reconnected the aircon electrical connector. Installed V belt after cleaning all the pulleys etc. Reinstalled fan cowling, fan assy, smallish Battery cover, air cleaner inlet, under trays (basically everything that was removed) and removed jack. Started car and made sure everything still turns correctly.

The compressor I received did not have the valve suction plate (the bit with the aircon pipe connectors) but rather a blanking/transit plate, at first I thought I’d bought the wrong one but after reading the instructions it became clear I hadn’t. I needed to remove the suction plate from the old compressor and install it in the new compressor. Make sure the surfaces are super clean, smear some compressor oil on the new seal etc. The new compressor came pre filled with compressor oil but way more than needed probably for transit purposes. You will need to drain out the oil from the old compressor and the new compressor into some separate containers of the same size. Compare the difference and replace the same amount of new oil into the new compressor that came out of the old compressor plus a little bit more. I drained the oil after removing the suction plates and refilled the new compressor after the suction plate was installed. You will need to re fill the new compressor via the hole that ‘sucks’. To find out which one it is, put your thumb on one of the holes and turn the compressor clock wise. You will soon discover which hole ‘sucks’ and which ‘blows’. After refilling with the correct amount of oil turn the compressor over clockwise a few times to distribute the oil inside then fit to the car. There were instructions with the compressor about all this but above is what you basically need to do.

ambermarine · June 15, 2020

Hi Paul

The description of your task is well easy to follow and will be a boon for anyone needing to replace the comp .

I am curious to know how you applied the 12volts to the clutch assembly as this is normally applied via a pressure switch that operates if there is enough refrigerant gas in the system if there is not enough gas pressure within the system the clutch will not engage.

This is usually the first sign that the system is leaking

runsgrateasanut · June 15, 2020

Hope this is not a "now he tells me" moment for Paul?

Razor61 · June 15, 2020

2 hours ago, ambermarine said:

I am curious to know how you applied the 12volts to the clutch assembly as this is normally applied via a pressure switch that operates if there is enough refrigerant gas in the system if there is not enough gas pressure within the system the clutch will not engage.

Thanks Phil, good question and of course you are correct. This was checked/done by the aircon guy, I watched, helped a bit and learned. I’ve had a think and going back to my electronics days I think I know. We removed the small 12v connector and with the engine running and switching the aircon on, checked the incoming side for 12v as you would normally do with a multi meter and is pretty standard. While I was mauling about removing the compressor side of the connector, pain to remove, so we could get one of the leads/probe into it, I think he must have rearranged the multimeter, switched to measure current and put it in series from the Battery positive to the compressor side of the connector ( normally to measure the current) but this will complete the circuit and therefore apply 12v from the Battery.

Razor61 · June 15, 2020

Forgot to say that the pressure in the system was good, this was checked first.

ambermarine · June 16, 2020

Thanks for that Paul, again very useful information and will be invaluable to anyone with a problem compressor.

steve2006 · June 16, 2020

The fact that the engine under cover was still attached surprised me, I’m down to my last good spare one now.

I always thought the PAG oil was a measured amount same with the required refrigerant quantity for a given system.

The AC guy should purge the system to remove any moisture then pressurise with nitrogen and UV dye to check for leaks then if all is good refill with refrigerant.

Personally I never turn mine off, I think it keeps things lubricated and it has never been re-gassed in 25 years. With a 4 litre V8 there is very little difference in fuel consumption and if the outside temperature falls to low it shuts down automatically.

A very good comprehensive tutorial BTW, make sure you come back with the finished results report.

PCM · June 16, 2020

Could NOT live without my a/c in a car.

Must haves: air con in the summer, all-season tyres in the winter.

At least that's what I think.

Thank you for a brilliant thread/post.

Razor61 · June 16, 2020

50 minutes ago, steve2006 said:

I always thought the PAG oil was a measured amount same with the required refrigerant quantity for a given system.

The AC guy should purge the system to remove any moisture then pressurise with nitrogen and UV dye to check for leaks then if all is good refill with refrigerant.

Personally I never turn mine off, I think it keeps things lubricated and it has never been re-gassed in 25 years. With a 4 litre V8 there is very little difference in fuel consumption and if the outside temperature falls to low it shuts down automatically.

Thanks Steve, a lot of the tips and advice about capping off pipes, draining and filling with oil etc came from the aircon guy so I can't take full credit for that. Actually removing the compressor I will take credit for though😉

PAG oil is a measured amount, if the condenser or evaporator is replaced as well the amount of oil to be put in the compressor is 40cc or 1.4 fl.oz according to the manual, which isn't a lot. I haven't replaced the condenser or evaporator so I presume I just need to put back in the compressor what I take out, that was the advice anyway.

Purging/pressurize/check for leaks, I presume he will do this and will check on the day especially because I've disconnected and refitted 4 x ac connections.

Flushing, I asked about 'flushing' the system because I wanted to do everything 'right'. Advice was that if the compressor itself was really knackered and there is metal contaminants in the system then yes 'flushing' is needed. The oil in mine was clean so no need.

Keeping the aircon on all the time, I agree and have always done it. Advice was that you wouldn't use more fuel than just leaving a rear window open (how true that is I can't say)

Pic of the oil removed from old and new compressor, LH green oil from old compressor - RH clear stuff from new compressor.

Razor61 · June 16, 2020

pic showing the transit valve suction plate on the new compressor. I didn't take a picture of the valve suction plate on mine but the picture on the right below shows it.

Razor61 · June 18, 2020

On 6/15/2020 at 4:25 PM, ambermarine said:

I am curious to know how you applied the 12volts to the clutch assembly as this is normally applied via a pressure switch that operates if there is enough refrigerant gas in the system if there is not enough gas pressure within the system the clutch will not engage.

Further to the quote above, below is a link to a YouTube video showing how to test if the aircon clutch is knackered.

Testing Aircon Clutch

Razor61 · June 20, 2020

Curiosity got the better of me and I decided to have a look at the old compressor to see how the clutch fits, how it works and how to remove it. First thing I noticed is that the pulley bit, it should turn free and smooth without the clutch engaged, wasn’t free. It was catching and didn’t turn smoothly at all. A bit of turning and it was smoother but not as smooth as you would expect. 10mm bolt in the middle removed and removed the first black front bit with holes in it, this is connected to the compressor splined shaft and there are a couple of shims. A metal ‘plate’ was next which was loose and I removed it. When removed it didn’t look right, debris and black gooey stuff in the middle. Not knowing how it all works and fits together I didn’t think anything of it much. I then removed a circlip and removed the pulley bit with a bearing in the middle. You could see where the pulley part had been catching on the magnetic clutch stator. Cleaned it all up and put it back together and tested if the clutch engages with 12v applied.........nothing so I’m pretty sure the issue is the clutch assy which was the initial diagnosis. I then looked at the parts diagram to see what bits I would need to ‘fix’ the clutch assy, I found that the metal ‘plate‘ which was loose shouldn’t be loose at all and should be a fixed part of the ‘Rotor sub-assy, magnetic clutch’ which isn’t available to buy anymore. That I think is the bit that broke. The whole clutch assy is available from Lexus at £450 but I paid £270 for the whole compressor so not worth fixing it. Anyhow I know I have a good mechanical bit compressor as a spare.

ambermarine · June 21, 2020

18 hours ago, Razor61 said:

Curiosity got the better of me and I decided to have a look at the old compressor to see how the clutch fits, how it works and how to remove it. First thing I noticed is that the pulley bit, it should turn free and smooth without the clutch engaged, wasn’t free. It was catching and didn’t turn smoothly at all. A bit of turning and it was smoother but not as smooth as you would expect. 10mm bolt in the middle removed and removed the first black front bit with holes in it, this is connected to the compressor splined shaft and there are a couple of shims. A metal ‘plate’ was next which was loose and I removed it. When removed it didn’t look right, debris and black gooey stuff in the middle. Not knowing how it all works and fits together I didn’t think anything of it much. I then removed a circlip and removed the pulley bit with a bearing in the middle. You could see where the pulley part had been catching on the magnetic clutch stator. Cleaned it all up and put it back together and tested if the clutch engages with 12v applied.........nothing so I’m pretty sure the issue is the clutch assy which was the initial diagnosis. I then looked at the parts diagram to see what bits I would need to ‘fix’ the clutch assy, I found that the metal ‘plate‘ which was loose shouldn’t be loose at all and should be a fixed part of the ‘Rotor sub-assy, magnetic clutch’ which isn’t available to buy anymore. That I think is the bit that broke. The whole clutch assy is available from Lexus at £450 but I paid £270 for the whole compressor so not worth fixing it. Anyhow I know I have a good mechanical bit compressor as a spare.

Always good to educate yourself when the opportunity arises and its a no loss situation,I found the water bottle float sensor was not working on my mark 4 when I bought it.

I bought a new one from Lexus fitted it but did some research on why the old one failed, it turns out they get saturated with the fluid and sink giving a empty bottle reading.

I dried it out and painted it with lacquer tested it for a month and it passed the test ,stuck it on eBay at half the cost of new and sold it to someone in Germany ,unusual to say the least but it shows benefits of education.

Razor61 · June 22, 2020

Aircon purged, tested and re gassed this afternoon. Everything checked out and works fine. Because it was a new compressor it needed to be run for 15mins, bit like running in a new engine. Total cost with new compressor, diags, de gas and then re gas (3 visits by Aircon guy) is £390. I have to be pretty happy with that.

PCM · June 22, 2020

2 minutes ago, Razor61 said:

Aircon purged, tested and re gassed this afternoon. Everything checked out and works fine. Because it was a new compressor it needed to be run for 15mins, bit like running in a new engine. Total cost with new compressor, diags, de gas and then re gas (3 visits by Aircon guy) is £390. I have to be pretty happy with that.

Great news - just in time for the sun!

Razor61 · June 22, 2020

8 minutes ago, PCM said:

Great news - just in time for the sun!

Absolutely..........heatwave this week so will be nice and chilled going home from work😃

Razor61 · June 27, 2020

Aircon has been working fine all week, which was very welcome given the heat, but the idle etc went wonky again. The cutting out issue didn’t occur again and I don’t believe it will happen again but it was idling high a lot and the car was driving forward at low speeds when it shouldn’t. I have replaced the coolant temp sensor and the idle was spot on after but it was done when the aircon wasn’t working. So, before I left work yesterday I reset the ecu by removing the fuses using the guide on here and it’s fine again now. It does vary a bit depending on whether the aircon compressor is engaged or not but that’s normal. In future when I change anything electrical I’ll reset the ecu in the same way as recommended in the guide.

m4rkw · June 27, 2020

Just curious, did you inspect the old compressor for damage? I've heard stories of impellers going out on them and then spraying bits of metal throughout the system. If that happens you need to get every last little bit of metal out of the system otherwise it'll just take out a new compressor soon enough.