Air Conditioning

Luckiest AC Leak Discovery Ever

Getting ready for some time in the desert, so after I did the 7.3-to-6.9 swap, I needed to recharge the AC system.  I figured I would pull a vacuum just to make sure it didn’t leak (it didn’t leak before, so I knew it was going to be good to go), and waited an hour.  Came back to find the system back to atmospheric pressure.  Wild.  It was a really slow leak, maybe one inch of mercury every 3-5 minutes.  I pulled another session of vacuum and tried to listen with a hose.  No luck.

The van is a PITA if you get a leak, because there is a front and rear AC system.  Lots of places where it could potentially leak.  Since I didn’t mess with anything in the rear or cab, I figured the leak had to be near the compressor or condensor.

I disconnected the vac pump and put my air compressor on the gauge inlet.  Put in about 20 psi and went back to listening with a hose.  I’ve never had good luck with doing the redneck stethescope, but I had nothing to lose.  Checked the connections at the condensor, and those were quiet.  Checked by the compressor, and that was quiet too.  I also checked the AC hose hubs in the back and by the dryer as well.  Nothing was apparent.

The leak was extremely slow, so I knew this was going to be a long shot.  I returned to the connections at the FS-6 compressor just to see if maybe I missed something.  We did remove the compressor during the engine swap, so maybe the connections were loose.  I put the hose in my ear and moved the opposite end around the compressor inlets and outlets.  By the passenger side connection, I heard the slightest hissing noise.  It was almost inperceptible.  I almost thought it was some static sound from somewhere else.

The more I scanned that area, the more I was convinced that slight hissing was my leak.  I took a 10mm socket and gave it a slight turn.  Open made it louder, closed made it quieter.  WOO!  Found it!

Unfortunately, tightening it down didn’t fix it.  I took off the connection and inspected the o-rings.  Sadly, one must’ve been cut during the engine swap process, which is likely since those fat AC hoses don’t nest out of the way very well, and we must have cut them on a exhaust manifold or cylinder head on the way into the engine bay.

I dove into my AC parts and found 2 sets of o-rings, but they were for VW’s.  My Ford sets were out.  Nothing would fit into the inset for the compressor with what I got in my supply.  I called around and found a Ford kit on the central part of town, got the set, and installed it right away.  Held vacuum for the entire night.  That’s tight.



Douglas Lum

Never heard of doing the “redneck stethescope” but that sounds cheap and effective! Thank you so much for sharing. Also did not realize the econoline had a front and rear AC system. fascinating. Getting ready to convert my 86 f350 from r12 to r134A. Gonna keep this trick in mind while checking for leaks. Thanks


Compressed air is not a good idea because it introduces moisture to the system. Nitrogen is what most people use. Pressure it up and use a spray bottle with soapy water to locate leaks.


that’s true. You don’t want excess moisture, but also, this van is 40 years old and not in the best AC condition. It’s really overdue for a full system flush and drier replacement. New orafice tube might be necessary, plus a new expansion valve in the back.


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