You need multiple vacuum pumps. Put one on each unit for 30 minutes. Charge beer can cold. How much superheat is in a can a beer?

No seriously maybe you have a flare nut leaking. Pump it up with nitro and soap bubble test.

 

I've confirmed there are no leaks in the several systems that have done this. They hold 400 psi nitrogen.

 

Pull longer vacuum, fresh pump oil, clean the micron gauge sensor and put nylon on your hoses. Are you using an evac system or pulling through manifold gauges? If your using manifold gauges there's your trouble.

 

Like I said, I've ruled out my equipment. I pull down every other system I work on without trouble, regularly going below and holding 200. I have also tried 2 different equipment setups, both work on every other system I've done.

Unfortunately, I don't have the luxury of pulling a longer vacuum since I don't get to these jobs until late afternoon. I'm hoping someone out there knows a trick to this. I wish these things had a liquid line service valve!

 

Unfortunately, I don't have the luxury of pulling a longer vacuum since I don't get to these jobs until late afternoon.

Then your customers aren't getting what there paying for. Vacuum by time is wrong period.

 

Multiple access ports, multiple pumps and time are your friend. 90 minutes isn't enough. I've pulled on multis over 8 hours before to get down to a good level. Just a ton of volume to evacuate.
Might want to check your recommended pressure test psi. All my equipment is between 500-600 psi for minimum 24 hours.
Are these conventional style outdoor units with only one access port? What size pump are you running?

 

Another thing, if you have any uncapped service ports, they will leak. They will sometimes be added to junction boxes or other places. Otherwise, 90 min, may not be long enough especially if it is cold outside.

 

The systems only have one access port. I'm using an Appion TEZ 8 with a 1/2" hose and core remover. Also tried using my SMAN3 manifold. No uncapped service ports. It sounds like there's no quick fix for this, and that the process needs more time than I'm alotted.

 

More time my friend. Evacuation isn't something you can hurry along.
I did a Samsung today with 3 indoor fan coils. Been holding 600 psi for close to a week so no leaks. Took around 4.5 hours to get the micron gauge down where I wanted it, holding of course. Thats pulling with an 8 CFM pump, both lines (it had service valves), cores removed.

 

Thank you all for your input!