97 850 A/C- Gauge Connections w/ Pump

[combatkarl]

I am sure this has been covered but I am unable to find it. I just replaced the evaporator and drier so thought the system evacuation was in order.
Using a vacuum pump and A/C gauges with low (blue), high (red), and recharge (yellow) lines, I have the A/C gauge connected as follows: blue line connected to the low port on the 850, the yellow is connected to the vacuum pump, and the red is not connected since the 850 does not have a high pressure switch/port, but is closed off in a loop.
1. Is this the correct connections?
2. How long does the vacuum pump need to be run? I cannot seem to get a vacuum reading. Possibly other leaks in the system?
Thank you.

[Ozark Lee]

The description of your line routing sounds correct to me. You need to have the high side valve closed, the low side valve open, and if you have the low loss style connectors at the ends of the lines the valve on the red line should be closed, the blue line should be open, and the yellow line should be open.

The real way to tell if you have sufficient vacuum is with a micron gauge but you can get close enough with the low pressure gauge. It has an area below the zero reference, typically in green, that goes to -30 PSI. You want to draw a vacuum until you get to -30 and then close the valves and turn off the pump and make sure it holds.

The amount of time that it takes to draw the vacuum depends on the vacuum pump that you have. It can take as much as an hour with a small pump and then I leave the system shut off for another hour to make sure that the vacuum holds.

A way to test your pump and make sure your manifold gauge set is properly reading the vacuum is to have the pump hooked up and both the high and low pressure valves on the manifold gauge set closed. The gauge should quickly (well under a minute or so typically) go down to the -30 mark since all you are pulling the vacuum on is the yellow line at that point.

...Lee

[combatkarl]

Thanks for the confirmation Lee. I re-read some posts and watched a couple of youtube videos as well. After being frustrated with the drier replacement, I didn't pay much attention to the gauges I had bought from the NAPA parts store. They must be an entry level tool as they only have pressure gauges designed for re-charging - meaning they don't go below zero. Since the gauges don't read "vacuum" - guess it's back to the parts store to return/exchange them or get the Harbor Freight gauges. The pump I'm using is from Harbor Freight (2.5cfm) and seems to be working as I can feel the suction through the lines when I connected the line to it.

[abscate]

Keep that vacuum pump upright and don't let the oil 'froth' - its not delicate, just don't bang it around or let it sit for an hour before pumping.

You do need a vacuum gauge to confirm both pump and down and holding vacuum - I tested mine overnight.

The system will pump down to near 0 psi in a few minutes. Keep pumping on it to get residual moisture out for an hour or two, though, then test.