A/C leak ... got a doozy here

The vehicle is a 1998 Chevy Express 1500 Conversion Van. I bought it used a few months ago so its history is unknown. The first few months we had it the A/C worked great in the cab area. No issues whatsoever. As far as we knew, there was no rear air as the panel for the conversion van stuff just says "Fan" and when you turn it on it blows air from the ducts throughout the passenger area of the van. You can heare a blower running in the left rear near the back tire so we figured it just didn't have A/C back there and was just circulating air.

A few weeks ago, the front A/C started blowing hot. I popped the hood and sure enough the compressor clutch wasn't engaging at all, even on max A/C. Jumpered the low pressure switch and the compressor kicked on just fine. So I figured it was low on R134. Put a can in ... still not blowing cold but it was only up to about 25 psi (low side). Only had one can so went to the store to get more. By the time I got back, 0 psi. So I figure there is a leak.

Picked up a can of R134 with UV dye in it along with the light and glasses. Crank it back up to about 25 psi with that. Shut off the van and notice I can actually hear a hissing in the area of the accumulator (really on these vans you have the evap tube, evap, accumulator pretty close). Before long it's empty again ... no pressure. No problem, I have UV dye right?

Because it's a van I have to tear it apart quite a bit to get access to all the lines. Pulled the battery, coolant overflow, air cleaner, engine cowling inside, etc. Can't find evidence of dye ANYWHERE! How could a leak that big not have the dye showing up.

Ah, but the plot thickens. Because I had the engine cover off, I can see the rear of the compressor and I notice a line coming off off it headed to the rear of the van. Then from under the hood I notice the evap tube has a branch that goes to the rear as well.

Crawl under the back of the van and notice a drip tube coming down from the are where the blower is ... it must have A/C! Due to the conversion stuff it was quite a hassled to get in there, having to remove a bunch of wood trim and even some lighting. Eventually I get the trim panel off and see an evaporator there with two hoses. Good, right? But no evidence of dye.

So at this point I'm trying to decide what to do. I could lift the van and trace those hoses, though they look to me like they travel through the side wall ... not good. And I had heard the hissing up front. So I decide to start there.

What I did:


Replaced the Accumulator ... I figure it's 12 years old anyway most likely and it's a cheap part. Plust that's where I heard the hissing. Also pulled the evaporator core but it looked good so I just cleaned it up (not flushed, just with compressed air on the outside) and put everything back together.
Get a set of manifold guages and a cheap air driven vacuum pump.
Hook up the guages and the vacuum and it can only ever get down to about 10 hG. Check the vacuum pump with a guage and it's at about 20 or so ... not enough for an evac but I'm just trying to find a leak.
In the meantime, the vacuum has dropped back to 0. Must still be a leak. To confirm, I crank it back up to the 10 Hg then hurry and disconnect the vacuum pump and shut off the air compressor so it's quiet. Put my head back over by the accumulator and the hissing is back ... just for a minute or two and then it's gone. Vacuum is back to 0.

Any ideas as to what to try next? Replace the evaporator core? Evaporator tube? Lines?

The one thing that is very puzzling about this is why the front air worked but he rear never did and then all of a sudden everything started working. And I hear the hissing up front so I kind of feel like this is unrelated to the rear (that could be a separate issue).

Any ideas would be appreciated.

With a leak like that oil and dye should be dripping onto ground--last G-van I did had a massive condenser leak- covered the entire bottom of radiator with dye--use a black light and ultraviolet glasses- under low sunlight-- like at night- to check for the dye- or get a 4 ft section of garden hose- put some charge in section and pin pput one end of hose to your ear- the other you scan the areas of concerns-- and hone in on the hissing.

The rear air with a conversion doesn't worry me-- it's the oem rear systems that the pipes corrode really bad underneath- yours uses rubber hoses- so no corrosion.

You may even have a "rub-through" on your rubber hoses underhood- seen that a few times-- look where hoses (or pipes) can be too close to oil dipstick, etc---whenever aluminum meets steel, steel always wins!

Thanks for the suggestions. I have the van up on stands and have been all around underneath with a blacklight. No dye except where some oil came out of the evap core when I was putting it back in. And nothing on the ground. That said, I can't see the underside of the radiator or condenser ... sounds like maybe I should bite the bullet and take off the grill, etc. to get at the condenser?

Also, on your suggestion to put some charge in it and listen for the leak. How much will I need to expect to see dye and or narrow it down by siound? And I have to run the compressor to charge it right? So I'll need to at a minimum put the coolant overflow and battery back in? Is there a way I can accomplish the same thing under vacuum? It's free and I don't have to run the van.

Wondering if I should invest in the $60 HF leak detector ...

You don't need to run the engine---heck, you can even used compressed air for a "hisser" -- or keep locating the leak with your vacuum method.

Well I went and got a real vacuum pump and now can get it up to about 20 ... but it drops right away. So I decided to put everything back together and put a can with dye in and see what I got. Did that and found something interesting. I get about 50 psi low side and 75 or so high side, with or without the engine / compressor running. So now I'm wondering about the compressor. But if that's the case, why do I hear the hissing way over on the other side of the engine compartment.

Confused at this point.

So what I have:

1. Won't hold vacuum for even 5 minutes
2. With one can of R134a in, guages read 50/75 and that doesn't change with the compressor on or off.
3. Can't find dye ANYWHERE

According to this page:

http://www.aircondition.com/tech/questions/82/

If the high side pressure doesn't change with the compressor engaged the compressor is shot Sounds like what I have. Would that alsp explain the leak or do you think there is a leak as well?

One more question. Is it possible to isolate parts of the system and pull vacuum to see where the problem is? Are there connectors, etc. available to do this? For example, if you took the compressor out of the loop, a way to hook the two hoses together or something like that.

If you have a leak the dye test or a sniffer should find it.
Have you run them test?
For high side high pressure leaks you have to get the system up to high pressure.