I don't have an A/C machine at home but I do have a set of gauges.
How can I pressure test the A/C system at home without buying lots of cans of A/C dye?

I was playing with the Imperial tonight. I flushed the heater core with water and it leaks. Yay. Finding another one will be fun.
Just for giggles, I pulled the cap off the A/C schrader valve. There was a bit of residual pressure in the system. Not much mind you, but there was positive pressure.
I spun the clutch by hand and the compressor seems to turn smoothly. I can't feel any appreciable resistance but there's hardly any pressure in the system.
I fired up the engine and jumped the compressor clutch. It kicked in without any bad sounds. There was no change in idle speed but I wouldn't expect that after turning it by hand.

I'd like to push my dumb luck and see if the mechanical bits of the system will work.

What's the best way to pressure test it at home?

The best way I know of is to pull a vacuum and see if it holds. Do you have access to a vacuum pump?

As far as the heater core, when mine started leaking in my 57 Plymouth, I had it re-cored locally.

I have never seen an AC system pressure tested. Instead they are evacuated using a vacuum pump. I bought a cheap one from harbor freight that operates off of a shop air compressor. You such all the air out and make sure it holds the vacuum.
Remember r12 freon is very very expensive, you may want to retrofit to r134a, but the oils used in r12 and r134a are not compatible so while the system is empty you may want to take the opportunity to flush it and get it ready for the r134a.

Another vote for a vac test (although a system that will hold vacuum isn't necessarily guaranteed to hold pressure).

At the risk of stating the obvious, you don't have to spend the $$ on R-12 to see if holds pressure. Armed with an adapter, you can use much cheaper -134a for pressure testing. Truth be told, you can even RUN R-134a in your system...

I know about vacuum testing the systems. I've done that on my truck and Concorde.
I was hoping to pressure test the system so I could find any leaks without going through a dozen cans of Freeze 12 with dye.

I'd have more time to mess with it at home during the week. I'm the late guy at work and only have an hour or so after work before they want to lock the facility down for the night.

What about the 134 idea of etevS then?

Vacuum isn't very accurate esp with the HF pump. Dry nitrogen is the way to test with a true pressure of what the system would run. 134 is great if you want cancer...

I never heard the 134a cancer link, but heck as long as it does not hurt the environment who cares how many PEOPLE it kills.

Ive done AC since the 80s.You pull a vacuum and let it set.See if it drops.Then you add a small charge and use either a black light or leak detector.I prefer the light as the dye is easy to see.If you have a leak you usually reclaim the 134 you put in.We did have a 12 machine at work but it hadnt been used in 5 years.I might have a heater core.I cant remember if I scraped the heater setups from my 70 Imps.Rocky

Dye is one of the best methods to get that done, you can try one of those little electric sniffers..however I've never had any luck with those. You can breathe on it and set it off.

when you turned it over by hand did you have the power on and the clutch was engaged or was it just freewheeling the bearing? .
if the system is low you cant energize the clutch therefor lock the clutch/pully and be able to turn the pump.

Those sniffers are very senitive and the tip can be ruined/tainted real easy. Never stick it into the hoses or touch anything with them.
If freon get's on it most times they need to be replaced, the sniffer tips.

AC sucks to work on without a recovery machine. I have been busy with AC repairs here lately. I am working on AC as I type this.
Most of my trucks lose about a 1/2 pound per year.

I just pull it all out, pull a vacuum and recharge with 2.2 pounds and reset the dash light. Good for another year until I find it 1/2 pound low next spring.

Never any leakage visable around any connections or hoses.

You would be better off pressure testing the system as well as vacuum testing. Your system may not leak under a vacuum, but under pressure it may. Under vacuum, the seals or O-rings will move in one direction and under pressure they will move in the other direction. This can and does happen. If you are able to, put a gauge on the low or high side port and then pressurize from the opposite port. Watch the gauge for 20-30 minutes to see if you have a pressure decay. That's my suggestion. It's based upon my experience as an engineer at one of the OEM manufacturers. In the recent past I spent several years working on the repair of HVAC systems on new units at the factory. We pressure tested all leakers with helium before evac'ing and refilling.
Just my 2 cents..............

That is what j do the Red Cheap HF Box.
My buddy who does home A/C has a,pump and does same thing. Sucks the system d own and leaves goes on another call and returns to see if it is ok to fill or not.

The fact that it has ANY pressure in it at all tells you it's sound. If it had a leak any bigger than what will get past the crank seal naturally over many years, it would have had zero pressure.

If it's still running R12, see if you can find some and just charge it back up. I would avoid those R12 drop in replacements if I could as my understanding is they are probably propane or similar.

If it has been previously converted to R134 then off to Walmart for a few cans.

Kevin