Looking for suggestions on finding an A/C line leak.
New 3G install, so new compressor and condenser.
Using the factory evaporator that worked when the 340 was pulled.
Bought a hydraulic crimper and made all new lines.
Hooked up HF gauges and vacuum pump, it pulled down to -30 within just a few minutes.
Turned off pump and it quickly, within 2 mins, leaked to -5 and settled there.
Plenty of hoses fittings and the adapters needed for the new style compresser, so the leak could be anywhere.
How do I track it down?

Is it normal for there to be oil in the yellow line, hooked to vacuum pump?
When I pulled the lines off the gauge, there was at least 2-3tsp in the line?
I also noticed the vacuum pump was not up to the fill line, where did that go?

Thx

use ac Dye & use the special light to find it

since it isn't up and running, to get the dye flowing and find the link you should also look at pressurizing it with nitrogen.
there are adapters to hook it to the a/c ports.

The leak is while under vacuum so I'm not sure the dye will work unless the system is pressurized even then without running the system I'm not sure the dye will travel through the lines. fell free to correct me if I'm wrong.

They use a gas to pressurize they systems and detector for that gas to find a "gross leak" such as this.

there also have been some issues with fittings needing to be "over crimped" to seal I believe that was mainly in the size 6's. what type of crmper did you use?

I might suggest inspecting every Crimp connection, o-ring and their sealing surfaces as a leak of this magnitude should be pretty easy to find (I SAID SHOULD). one could also try water or compressor oil while under a vacuum to see if it gets sucked in.
So be aware that the o-ring's seal on the ID and OD and that is where you need to look for lateral damage on the sealing surfaces and rings
keep us posted

This , pressurize the system and see if it leaks down first.

Close. Pressurize and RUN the system. You need to get the oil and dye to circulate in order for the dye to show a leak point.

Every connection and adapter is suspect. Including the gauges. Schrader valves are a common leak point.

If the system didn't leak before the engine swap, good bet the evaporator core is ok. Condenser? New or original?

If you have the right fittings, it's possible to Pressurize the system with shop air and go over parts with soapy water.

Don't have nitrogen, so I guess I need to throw some R134a with dye in it and see what happens.
I used reduced barrier hoses for flexibility, there are #6, #8, and #10 fittings.
The condenser is new, but odds are 1 of the crimps or the adapters to the compressor are leaking.

I haven't even wired up the electrical yet, need power to the compressor and the low pressure switch on the dryer, yet another leak possibilty.

This has been my experience, if I crimp to the recommended limit line they're more likely to leak. I over-crimp all sizes. If you have the means to make adapter fittings, you can pressurize the hoses with shop air and test for leaks with leak testing solution or soapy water.

I had read some of issues, so I went to town and really clamped the h*ll out of it.
Can too much pressure on the crimp cause a problem?

Sorry but I am sometimes a victim of the Evelyn Woods "SPEED READING" course Intel had me take many years ago
Did you close the valves on the gauges before turning the pump off????

I did not, didn't see that on the gauge/pump directions.
Could it be that easy (that I'm a dummy)?

always need to "close" the system before turning off the vacuum pump.
i use a small ball valve in the pump line to do this, then turn off the pump.

I would evacuate the system, if filled with refrigerant, and fill with nitrogen. Use soapy water, or better yet, a leak detector (fluid) used in home hvac systems. I pressurize to 250 in home systems. Keep in mind, you could be chasing a ghost. I've seen em leak only while running out of a copper line from compressor. Hard to soap with the fan running!

Might just be it. Try again and see!

How long did you leave it at -30? If there is any moisture in the system you may need to leave it at a deep vacuum to "boil" the water off. Also, if it stabilizes at -5 and does not continue to raise, it may be temperature equalizing. Hold it over night and see what it is.

As others have said, turn of the gauges before you turn off the pump and consider the above.

Closing the gauge valves Isolates the pump. If there is a leak the gauges will creep up.
I have ball valves on both lines so I can isolate the high and low side.

To the OP, yes it could be that simple.

What I am not sure of is what effect if any the pump oil may have I believe the do make a "FLUSH" for the system 🤔 but I am not an expert in this area.

one other thing to be aware of is when you do hook up the freon to charge the system, use the schrader valve to burp the air out of the line and manifold before opening the valve to start charging. If using small cans you must close the charging valve before removing the empty can and burp the line again before reopening