I would have to guess that the magnitude of pressure is significantly higher than the vacuum that is drawn on the system in order to fill it. So when you pull a vacuum to check for leaks, you're not pulling nearly as hard as the refrigerant is pushing once the system is charged.

 

I pulled a vacuum for about an hour after replacing that hose that was damaged. The vacuum now holds! 😄 This time, only a little smoke/vapor came out of the vacuum pump and at some point, stopped smoking. I'm not sure exactly when because I was doing something else most of the time. Was glad to see it since before it was pretty much smoking like a chimney and sputtering oil the whole time no matter how long the pump ran

I didn't have enough time to sit and see how long it held after turning the pump off because I had to go to work, but it did stay at 30 inches of mercury, unlike before. I will maybe pull another vacuum for another hour again tomorrow, I guess?

How would you suggest I pressure test it? By adding refrigerant? Or the nitrogen approach? I was looking to get a canister but couldn't find where to get it and everything else needed. Do mechanics typically pressure test using refrigerant? Thanks

 

When I ran the shop before I retired, we would add refrigerant with some dye. The dye seems to disappear rather quickly so check with glasses and a black light soon after and repeat before a week has gone by. We have had lots of issues with evaporators getting plugged by smoke and dirt physically. The steel body Fords did not have cabin air filters and we are in the Pacific Northwest. We are a large power utility and have had some tremendous fires over the last 8-10 years. We have to go into smoky areas to restore power. We have some older trucks that need to last one more year and become quite expensive to make it to the end. The latest example is showing green out the evaporator drain and smells like freon in the dash vents. It lasts about a month before it quits cooling. This will be the third evaporator for this truck. It is a 2011 with 17000 hours on the engine. The hvac box is the first thing they put in the cab so it all has to come out to replace the core.

 

After I got an evac and recharge at one point a year or so ago, I recall smelling what might have been refrigerant somehow getting into the cabin. It would get to where I had to roll my window down for about a minute to air it out. After researching and all the time that has passed, I feel like the evaporator has been the initial issue this whole time. Hopefully, I'm wrongI wish there was another reason the smell could have gotten unto the cabin, like the expansion valve seals or something.