Depressurise the aircon system to remove V12 cam covers?

Hi Folks,
Been looking through the XJS Repair Operations Manual on instructions to change the V12 cam cover gaskets.
According to the ROM, the air conditioning will need depressurising and I was wondering if that was necessary and if it was, is that process best done by a proffecional.
If it is a DIY job to do at home, would any specialist equipment be needed to do it.
When the job is complete then I guess a trip to the garrage would be in order to have the aircon repressurised.
Thanks for any input.

DO NOT RELEASE the refrigerant to the atmosphere!

You will need a recovery tank with a wye valve, a vacuum pump, and a recovery machine, along with their hoses, and a manifold gauge set.

I am doing that now.

I bought a recovery tank, get a 400 psi tank for 134a refrigerant (older types like mine used R12, which only require a 350 psi tank, but by the stronger tank anyway.

I already had a vacuum pump. When you get the recovery tank, it may be filled with nitrogen or with air. Regardless, open the valve and release the nitrogen into the air (which is no problem) or verify that the tank is at atmospheric (open to atmosphere) pressure. Connect the vacuum pump and manifold gauge set to the tank, closing the necessary valves, making sure there is the proper amount of compressor oil in the vacuum pump, turn on the vacuum pump and watch the gauge take the tank down to nearly a complete vacuum (my vacuum pump took the tank down to just over 28 inHg (28 inches of mercury vacuum, close the tank valve to the vacuum pump, then turn the pump off. Read the gauge, then come back in 15 minutes or so and the gauge will read the same if nothing is leaking (mine has been holding for about 5 days now).

Here is the more expensive part: the recovery machine. Being as I don’t have a recovery machine, but my house HVAC contractor was out last week for regular service on the house systems, I asked him if there was a place to rent a recovery machine near where I live (there isn’t) and he said let him know when I am ready and if he is not doing a change out where he will need his recovery machine, he will bring it by for me to use … I am now waiting for that … :smile:

The recovery machine will recover the refrigerant from the car’s system and pump it into the recovery tank. When you are ready, you can recharge the car’s system from the recovery tank.

A decent recovery system is $500-$750, so I am willing to wait, and wait, and …

If you don’t have a vacuum pump or gauges, and haven’t started taking things apart, by a recovery tank (I got mine from Vevor), drive to your mechanic, have them recover the refrigerant to your recovery tank, then take it back and let them recharge from your tank (keep your refrigerant so you don’t have to buy more).


You don’t need to depressurize the system. Unbolt the compressor, and move it aside. Don’t disconnect the hoses. There is enough slack in the hoses to move it to one side or lift up the back end while you remove the valve covers.


Jon, I have my compressor hanging out of the way, but to get to everything easily (at least for my definition of “easily”), I need to recover the refrigerant from the system, break the connections and fittings loose, and get them out of the way.

I will reconnect what I can after setting it aside, putting a vacuum on it to keep moisture out of the system while it sets there out of the way.

Maybe I am doing more work than is necessary as a minimum, but doing that work will make doing all the other work I am going to be doing much, much easier … at least in my opinion.

Support used as “3rd hand” for removal of hood and other “need a 3rd hand to hold this” jobs.

Compressor hanging from support until refrigerant is recovered.


Hi Jerry and Jon, thanks very much for both of your input on my query.
Jerry, thanks for the very detailed procedure method you spent time writing up. It seems very involved and possibly fraught with disaster if not followed to the letter.
I suppose at some point (just like the coolant system hoses and fuel + injection hoses) the air con hoses will degrade and require complete replacement.
I admire the overhead gantry you have set up to assist with the job in hand.
It is a long time since I looked under the bonnet of my project car (which I am about to restart doing work on) bu from memory ( the hose coming from your compressor to the right hand wing in your puoto) is disconnected and laying near the wheel arch on my “right hand drive car”, and I am not sure if it is blanked off or open to atmosphere. I will be finding out shortly.
The car came to me like that 20 year ago, and has now stood basically untouched for the past 19 year, burried under the trappings of life and the passage of time.
Many thanks to both of you for your replies.

Andy, if any hose is disconnected, or if any fitting is loose or has been loosened, the system has already lost its refrigerant charge.

If any hose or fitting is disconnected, anything could be in that hose (insects, bugs, dirt, whatever, but especially moisture) and the hoses and system would need a good examination to make sure it is useable.

If any hose or fitting is disconnected - the system will need a vacuum pump connected to make sure all the moisture is removed, and that is after verifying that there is nothing else in the system.

Yes, all types of hoses will eventually need to be replaced, but I am hoping that the ac hoses are still good (I will visually inspect them, and most importantly, put a vacuum on them. Putting a vacuum on something will reveal minute leaks quicker than pressurizing and looking for a pressure drop. Does not take much of a leak to not even be able to pump it down to a vacuum, and smaller leaks will show once it is down to a vacuum. If the system holds vacuum for 15 minutes, typically the system is considered good to go, so I put a vacuum on it and then expect it to hold for days without evidence of a leak. After all, the refrigerant is under pressure and is expected to hold in there for years without leaking out.

I will be removing the radiator, the condenser core and hoses, so that I can remove body panels for cleaning and painting. Thus, in my case, just being able to move a couple of hoses around is not going to provide the working space I will need.

My ac service contractor should be dropping his recovery machine by tomorrow or the next day, so my waiting time is almost over.

Thanks Jerry,
Sounds like you are on a mission.
I will be on a mission when I get ‘Felix’ out of the garage.
He actually had four road wheels on him last night (first time in about 19 years).
Lots of welding etc to do, hope I can save him.