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Paul Ricard

Joined: 28 Dec 2012
Posts: 3067

1999 Porsche 996 Carrera 2

PostPosted: Sat Jun 07, 2014 10:28 am    Post subject: Air Conditioning compressor DIY guide Reply with quote

Well my air con gave out the other day. My fault was pretty obvious as seen below. Don't buy a compressor from Porsche - I got a new one for under £200 - they are the same as fitted to many cars (but with different pulleys), the 996 shares its pulley with many Audi V6s.

With air con faults, the first thing to check: Is there pressure in the refrigerant pipework? You need to hook a gauge up to the valves next to the screen washer filler. If not get a specialist to pressurize the system with nitrogen or UV dye and find the leak, fix and refill.

In my case I had a leak from the compressor.

The compressor is a pump that the engine turns which compresses refrigerant to a liquid and pumps it to the condensers at the front of the car.

The compressor doesn't run all the time. There is an electrically operated clutch, which switches it in and out. This clutch is mounted to the compressor by a hub and a rubber isolator. If the compressor seizes, the isolator will give out to save the rest of the accessories (alternator, water pump etc).

In my case the compressor had seized and the isolator given out. New compressor time!

You can remove and inspect the clutch and isolator without removing the compressor - no need to take belt off. Just undo the 10mm bolt on the front and slide it off.

If your compressor bearing is grumbling (while aircon off), just remove the drive belt, clutch hub, snap ring and the pulley slides off complete with bearing - any local supplier should be able to get you one.

My compressor, as you can see the isolator has given out and melted after the compressor seized.

The hub, and clutch plate should be one piece but mine was separated:

You can remove the drive belt by relieving tenson with a 24mm socket on the pulley and slipping the belt off:

Here you can see the pulley held on with a snap ring.

Pulley removed showing bearing code- you would need to grind the indents out and press the bearing out to replace a grumbly bearing:

With the belt removed you should be able to turn the compressor (clockwise) by hand. I couldn't so determined my compressor was seized.

So now I needed to get a new compressor!

I found out the originally fitted Denso 7SB16C fitted to a 996 is fitted to loads and loads of other cars. If your pulley / clutch is fine you can swap it to a used 7SB16C from a zafira, whch you can get used for as little as £20. Since both my compressor and clutch were shot, I needed the lot. And since I was paying to have the system checked and refilled by an air con guy, I opted for a new one.

The 996's pulley setup is shared by a load of VAG cars with V6 engines. I found a Nissens 8904 compressor brand new with 2 year warranty for under £200 by an ebay seller, here it is:


See those 2 little O ring seals? They are for where the pipes joining the compressor. Porsche wanted £9.50 for those two seal alone! Those came with my new compressor.

I'm going out to fit it now..... Obviously I'll need to find why my old compressor seized, and flush the pipework of any debris before fitting the new one.
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Joined: 05 Jun 2013
Posts: 244

PostPosted: Sat Jun 07, 2014 12:07 pm    Post subject: Reply with quote

superb... great info .. let us all know how it goes.
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Paul Ricard

Joined: 28 Dec 2012
Posts: 3067

1999 Porsche 996 Carrera 2

PostPosted: Sat Jun 07, 2014 7:39 pm    Post subject: Reply with quote

To remove the compressor:

First of all remove the power steering fluid reservoir. I didn't at first, but it would be a bit easier with it out of the way.

To do this use a syringe or turkey baster to suck as much fluid as poss out and put in a clean jar for reuse. Attach a tube to the syringe and get it out from below where the reservoir attaches to the pump.

Then there is a 10mm bolt holding it on, and the connection to the pump just turns 1/4 turn anti clockwise and pull it out.

Now to remove the compressor - examine your new compressor and note where the rear mounting bolt is. On your car there will be a pipe in the way of this, and you have to get to it from above the intake. There is a temp sensor in a grommet above the compressor attached to the plastic intake. pull this out and remove the rubber grommet.



You'll need a 13mm 1/4 drive socket and wobble attachementwith an extension to get to the rear bolt. You will also need slender hands! put your hand in where the temp sensor came from and feel the bolt and locate the socket.

Undo the two front mounting bolts and pull the compressor forwards with pipes still attached. The rear bolt will hang down and catch on things so a hand there will hold it up - you can't remove it as the pipe is in the way.

Disconnect the wiring and undo the pipes (make sure there is no surplus pressure in the system before undoing these!) take care not get any muck on the ends of the pipes.

Mine had a female spade connector which didn't match my new compressor, so on my new one I cut the connector off and fitted a matching spade.

Compare the new and old compressors to make sure its going to fit and the pulley is the same size and offset:

At this point you should triage the old compressor and work out why it failed. If there's metal particles in the oil you are going to have to find someone that can flush your system out, as this will probably kill a new compressor. This is the case with mine - see diss-assembly in the post below.

If there is no evidence of contamination then you can probably just reassemble.


Fit new o rings (my new compressor came with them) to the connections and fit the pipes to the new compressor. Before connecting the pipes be sure to put the rear bolt into the new compressor as the pipework gets in the way.

I left my pipes disconnected and tucked out for the way as I need to get my system flushed (see below).

Connect the wire and wiggle the compressor back into place.

Use the wobble extension again to get the rear bolt tightened.

The instructions with my new compressor state you should turn it a few times manually to prime it.

replace your power steering reservoir and squirt the fluid back in, top off if you spilt some.

Replace the belt and your airbox.

(note my pipes ends protected and tied out of the way ready for system flush)

Get the system recharged by your friendly local air con person.

Enjoy cool air Smile

Last edited by wasz on Sat Jun 07, 2014 8:00 pm; edited 2 times in total
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Paul Ricard

Joined: 28 Dec 2012
Posts: 3067

1999 Porsche 996 Carrera 2

PostPosted: Sat Jun 07, 2014 7:54 pm    Post subject: Reply with quote

Compressor Post-mortem

Its important when you have the old compressor off to take it apart and work out what went wrong:

Clutch plate off as before via 10mm bolt.
Remove snap ring and then pulley.

Leaves you looking at the electro magnet cluctch actuator:

Another snap ring and this comes off

Remove the 8 long allen bolts that hold it together:

Compressor is in 3 parts I will call L-R the "head", the block and the valves:

Close up of the block containing pistons shows contamination with metal particles:

The head is completely mangled, this is where the swarf is from:

In there is an offset disc, that as it turns pulls the pistons in and out. Something has come loose and completely destroyed this.

This area should be lubricated, but is dry and full of crap.

More bits in the end cap, you can see the bearing is still kinda functional....There is a seal beyond the bearing that is a common failure point.

I really have not got lucky with this, its destroyed and exited swarf through the system.

My best guess is something blocked the oilway to the head, and this overheads and fell apart destroying itself.

Sooo.... I need to get the system properly flushed which involves squirting a solvent under pressure round the system until no more crap comes out, a fairly specialist job. I'll be on the phone this week finding somewhere that will do that for me before hooking my new compressor up.
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Paul Ricard

Joined: 28 Dec 2012
Posts: 3067

1999 Porsche 996 Carrera 2

PostPosted: Tue Jun 10, 2014 10:00 pm    Post subject: Reply with quote

I have found a local place that will flush and re-seal my air con system.

They are charging £45 to flush with solvent then blow through to dry with nitrogen.

Then £45 to recharge with refrigerant.

the O rings are all pretty standard so don't go paying Porsche £3 each....

As I'm flushing the system I need a new receiver dryer and expansion valve as they might be contaminated with particles from the compressor.

The dryer contains desiccant and absorbs moisture from the refrigerant. I paid £17 for one.

The expansion valve reduces the system pressure on entry to to the evaporator and is located near the battery mounted on the "firewall". I paid £23 for a new Delphi one on ebay.

If anyone else needs to do this job compressors are bit cheaper here: £175 - and they sell dryers and expansion vales at a good price:

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Joined: 03 Jul 2013
Posts: 476

PostPosted: Tue Jun 10, 2014 10:32 pm    Post subject: Reply with quote

Good info, thanks for posting. That will be useful for 'searchers' in the future I'm sure.

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Paul Ricard

Joined: 28 Dec 2012
Posts: 3067

1999 Porsche 996 Carrera 2

PostPosted: Sun Jun 15, 2014 10:32 am    Post subject: Reply with quote

Sorted, total cost to me £340

£200 compressor, £40 dryer and expansion valve, £100 flush and recharge

The new compressor came charged with oil- but the 996 with long pipes needs more than it was pre charged with.

Worth draining and putting the correct amount in!
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