Automotive Air Conditioning Information Forum

Hi all, I'm new here.

I'm trying to pump down the system on a 98 tacoma. I've got a cps micron gauge, and I'm using the autozone loaner manifold gauges & vacuum pump. I've checked all of my fittings, replaced the oil in the pump, but ~270 is pretty much the lowest I'm able to consistently go. It fluctuates a bit depending on how I mess with the valves on the manifold gauges; sometimes I can manage to build up enough suction to drop the numbers a bit by opening & closing the valves. The lowest I've been physically able to go is around 200-230, no lower, but it usually hangs out around 270.

Anyway, assuming I can let this go as long as I want (this is for my own vehicle), should ~250-270 microns be good enough? I've been running the vac pump for hours for the past couple of days, and the overnight decay brought it up to around 350-400 microns, which seemed ok.

I've also stopped seeing moisture bubble 'eruptions' where I'll see the microns suddenly jump up and then drop back down lower than they were before. So, I'm assuming this is a good thing, and that system has stabilized, right?

Should I be ok even if I can't break the '200 micron' barrier?

A reading of 500 microns or lower is considered excellent.

Thanks for the quick reply.

Yeah, most of what I've read & seen mentions 500 microns as being the 'standard,' but I've also seen a bunch of videos of guys being able to pull down to below 100 microns, so I started to have some doubts if I was actually going low enough at 270 microns.

Another question: Should I be worried about having pulled down to ~250 microns for so much time? Will it suck out the oil or affect the system negatively in anyway?

Also, is it true that vacuum won't help pull moisture out of the dessicant in the receiver/dryer? I just put a new R/D on my truck, but then I found a leak that needed to be fixed, so I ended up having to purge the system & start over. The R/D was only exposed to air for a couple of hours, and I was hoping that I wouldn't need to replace it again; I figured that pulling vacuum on it again would help to dry out whatever moisture it might've absorbed during that time, but now I'm not so sure.

No need for concern. Reaching ~270 microns is better than many vacuum pumps can achieve. Since it's your own vehicle, you can keep the pump running for a few hours or even overnight to ensure that you remove all the air and moisture.

Unlike a recovery machine, evacuating a system typically doesn't remove any measurable amount of oil.

Many pros recommend replacing the R/D every time the system is opened. They're cheap insurance, providing peace-of-mind that you won't have to do the job over if the existing desiccant is in fact saturated. However, evacuating the system won't "dry out" the used desiccant.

My goal was always 400 microns. The last green LED on the old Supco gauge. I have moved on to different equipment, but the number stuck with me.

I will second John's information about desiccant. It will over time get saturated. Our vacuum pumps can't remove moisture already in the desiccant.

Wow, mention of that old Supco brings back memories...

I often find that if I am pulling down an existing system, that there is refrigerant still dissolved in the oil, and that sometimes wont let me get below 1000 unless I let the pump run excessively to rid the oil of all refrigerant.

hi
Suggest u leak check manifold and hoses
1/pressure test refrigerant with nitrogen 300psi
2/ vacuum check
2a check pump with micron gauge only should get to 0--50 mic
2b pump down each hose with micron gauge ,take note of reading
2c pump down manifold with hoses capped, micron connected then operate taps if microns jump up/down you have a leak on the tap spindle shaft
2d not as accurate but if u have a leaking h or L gauge plug connection point and see if there is a difference