Warm weather is finally here and that means it’s high time to finally finish work on my AC system!
My car has the Delanair Mk 3 system typical of '89s. It’s been converted to run R134a by a PO but developed a leak (since addressed by me) and got down to virtually no refrigerant pressure by the time I bought the car.
System appears to be leak tight now so I am getting ready to vacuum it (firstly to verify my handiwork and that it is leak tight) and then to enable it to accept new refrigerant. Anyone have any tips or advice for the vacuuming and recharging process?
If you removed any parts you want to change the drier! There must not be a trace of water in the system. Driers are cheap. For vacuuming you probably want to go to any AC shop, and they will probably make cheap and fast work of it?
If you can vacuum yourself, and have the equipment, go by the workshop manual
David
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
3
Warmer is better. Heat increases the pressure of whatever is in the circuit (air, moisture, whatever) and hence makes it easier to vacuum out.
dmaggs, this advice is based on my HVAC work on residential and commercial AC systems for buildings work but I believe that it still applies to any AC system,
Pressurize the system using nitrogen to look for leaks up to say 30 to 40 psi using soap and water checking for bubbles at any fitting initially. I just fill a plastic spray bottle with dishwashing soap and water and spray all fittings and connections.
This works for checking most leaks especially big leaks.
Nitrogen is not that expensive to check system under pressure and your not supposed to just use compressed air because of the moisture that would be in straight air.
I have a vacuum pump that I use for my business, It’s over $250. Probably not worth it for just one car project. I did notice Harbor Freight carries vacuum pumps. They priced much cheaper but don’t know if they are any good.
You can also check for leaks by placing an AC system under a vacuum but you would need a vacuum gage that read in microns.
AC manifold gages will read to say 29.5 hg but a micron gage basically reads deeper and really the only way to be absolutely sure you have no leak.
Typically with my HVAC work, if I can reach and hold 500 microns or less, the system has no leaks. I have a Yellow Jacket vacuum micron gage that can be bought used on ebay for less than $200. Maybe not worth it for one car project but if it passes the vacuum gage test, I’ve never had an AC system that needed refrigerant again after checking it under 500 microns of vacuum.
Hope this helps!
jdere,
It’s interesting that you mentioned nitrogen. I bought a small nitrogen tank, regulator, and some adapter fittings last week at a local welding supply shop to help me sort out some of my inoperative car A/C systems.
After throwing thousands of dollars at A/C shops over the past 20 years only to have those cars blown only warm air shortly afterwards, I decided to take on a lot of the A/C work on my Jaguars myself. When starting out on a car that once had a fully operational R12 A/C system but now has no refrigerant pressure I check that the compressor clutch worked, I replaced all the o-rings, I replaced the receiver drier, and then I connected a vacuum pump to verify that the system would hold 30 inches of vacuum for a week or more. If it did hold vacuum then I took it into a licensed A/C shop to get it recharged with R12. If it didn’t hold vacuum then I did further work to isolate the source of the leaks until I could get it to hold vacuum. Of course I understand that holding vacuum is different than holding pressure, so I wanted to test that the system held pressure using a relatively safe gas. That led me to get the nitrogen.
I hope to get my the A/C system in my 1984 XJ6 Vanden Plas working again after a recent engine swap. It turned out that the original compressor would not hold vacuum so I got a replacement rebuilt compressor. I plan to complete the system reinstallation this week (including all new o-rings), test it first for holding vacuum, if that works I will fill it with 30-40 PSI of nitrogen to see it will hold that pressure for a while. If it does I will evacuate the nitrogen and get it recharged with R12.
Thank you for confirming the nitrogen approach that I was planning to use. I have three more Jaguars with inoperative R12 A/C systems that I plan to get working again after years of expensive and disappointing results of trusting others to do this right only for those systems to blow warm again shortly after being worked on. Their typical answer about that was “well, we fixed the problem you had, so a new A/C problem must have developed.”
Paul
1 Like
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
6
I have one, an ejector type vacuum pump. It comes in a cute box, but I threw the box away and just kept the ejector block itself. It’s about the size of a deck of cards.
They’re not the best vacuum pumps, but they will do the job. Ya gotta help 'em out all you can. First step is to purge the entire system using nitrogen, so you’ve already gotten all the air and moisture out that you can before you even start the evacuation process. Second, you can evacuate it twice: evacuate, then refill with nitrogen, then evacuate again. Third, you can do all this with the system as warm as possible. A nice hot day is good. Putting space heaters around to heat things like the condenser up also help.
Remember that a proper evacuation takes time. The idea is to get any moisture in the system down to below its boiling point so it vaporizes and can be sucked out. But even with the pressure low enough, it takes a while for that moisture to actually vaporize. That’s why when you first pull a vacuum, sometimes it drops back a bit even though you can’t find a leak. It’s not really leaking, it’s just the moisture inside turning to vapor and hence reducing the level of vacuum. It’s also why it’s a good idea to hold the vacuum for a while; it ensures that the moisture has entirely vaporized.
