PatHenry

Ok, so this is an extension of my 2 previous threads:

Part 1 - https://www.cherokeeforum.com/f2/c-q...novice-245505/
Part 2 - https://www.cherokeeforum.com/f2/c-q...rt-2-a-245953/

So I've got all the o-rings replaced in my A/C system except for the top one on the condenser since I can't get the line off due to excessive rust.

I bought a set of HF A/C gauges and a compressor activated vacuum pump. I hooked everything up according to the instructions and put a vacuum on the system. The vacuum read about -13 and held that steadily as long as the vacuum was connected. Per the excellent advice thus far I'm looking for something like -30.
Wondering what was up, I took a look and it seems that the compressor I have has a lower CFM rating than the vacuum pump (3.xx on the compressor vs. 4.xx on the vacuum pump).

So my questions are:
1 - Given the conditions described, is this more likely that the pump isn't strong enough or that I have a leak preventing the vacuum from reaching the proper level?
2 - If I have a leak, what is the best way to diagnose/find the leak? Given that I'm putting vacuum on the system, if I blew smoke around the system would it get sucked in at the leak location?
3 - Do I need to get a stronger/better vacuum pump and if so, what specs are required (2.5CFM, 3CFM, more? )?
4 - When I removed the lower condenser hose, a bunch of oil drained out. I'm assuming that this is the PAG oil for the compressor - is this normal/expected?

Thanks guys!!

4.3L XJ

To see if there is a leak, suck it down as far as it will go with the gauges hooked up and the pump hooked up to the yellow hose. Close the yellow valve and see what happens. If it gets less vacuum then it has a leak. If not, it is the pump

Rambler65

From what I understand you need a really good air compressor to run that type of vacuum pump. (Admittedly I have not tried one myself since I know my cheapie direct-drive 115V air compressor would not be up to the job.)

Does the AC system hold the vacuum you are getting when the pump is disconnected? If not, you still have a leak somewhere. If it does hold, I'd suspect that you need to use a motor-driven vacuum pump to draw it down further.

PatHenry

You're not kidding about needing a serious air compressor to run the compressor vacuum pump. I have a very nice craftsman that I thought was good, but it only puts out 3.x cfm @ 90psi.

I ended up biting the bullet and bought an electric 2.5 cfm pump for auto a/c. It was between the new compressor (oil lubed) @ $120-ish or the electric pump @ $72.
I also picked up an in-line valve since the HF gauges don't have a built in valve on the yellow line.

I'll hook everything up tonight and see if I can get it down to -30 and see if it holds.

I have the whole front grille and stuff off (to access the condenser fittings); I figure that if I need to replace the condenser, or if that one stuck fitting is leaking, I can do that before putting the stuff back on.

Any advice on finding a leak in an evacuated system?

jordan96xj

While holding the -30 vacuum is a step used to check for leaks, I think pulling the -30 vacuum for a set amount of time is also important step for removing atmospheric moisture from the system (the moisture that came in from the world when you opened the system up, due to humidity). I think if the vacuum is not strong enough (e.g. 30), it won't cause any condensed moisture that exists to evaporate and make its way out of the system. So its good you got the right stuff in order to not skimp on that. I think failing to pull the moisture out is referred to by the pros as putting the system back together "wet", and its a big no-no and will lead to premature failure. Some run the vacuum for as little as 30 minutes, some for as long as 4 hours in order to get the moisture out. I think I ran mine for an hour (maybe 2, can't remember).

Vacuum drop helps to show that a leak is present. Not so good at showing where the leak is. I have a leak detector (sniffer). So I would charge, then find the leak, then evacuate again if need be to do more repairs.

I tried to do a google search to see if there were any spiffy ways to find a leak location when under vacuum, and there were no easy answers. Because most folks would prefer to use a sniffer, but that doesn't work with vacuum, only under positive pressure with refrigerant present.

PatHenry

The moisture removal was on my mind since I figured that -13 was not enough to ensure that it's all out.

Hopefully it will just hold vacuum with the cutoff valve in the yellow line and I won't have to worry about it. However if it doesn't hold vacuum I guess I'll try some smoke and see if that does anything. At that point, I may try heat on the last fitting and risk the damage to the rubber on the hose. Worst case I'll replace the condenser and the upper line. I'm hoping I don't have to do that since the replacement parts appear to have an intermediate line between the condenser body and the hose connection. My condenser definitely does NOT have that intermediate line, the hose runs right to the condenser body as a single unit.

I'll report back with how it goes.

Rambler65

The other thing is that just because it holds vacuum doesn't mean it will hold pressure! The advice you are getting about looking for leaks while the system is pressurized is correct. Unless a leak is so bad that you can hear the air being pulled in you'll never find it under vacuum. Not a good idea to let it pull in smoke or other contamination.

I also have an electronic "sniffer" to detect refrigerant leaks. The most common alternative is to charge in dye that will glow under UV light. You can also look for telltale signs of refrigerant oil at fittings and hose crimps. Unfortunately that doesn't help much if the leaking part cannot be seen. (Like the evaporator which is a major cause of leaks on these vehicles.) A sniffer held under the condensation drain will detect evaporator leaks.

I'll typically pull vacuum on the system at least an hour to pull out moisture, preferably more. It is still important though to expose the AC system to atmosphere for as little time as possible. The problem is that the PAG oil used with R134a readily absorbs moisture (like 100x more than the mineral oil used in old R12 systems) and that moisture is not released under vacuum. This forms acids in R134 systems that over time can eat tiny holes in metal parts.

Having fun yet?

4.3L XJ

The first thing I will say is that to find a leak, you need to pressurize the system to at least 200 psi. Home and commercial systems to 400 psi. Then you get the soapy water sprayer out and look for bubbles unless you have dye in the system before shutting it down for repair. As far as leaking, by experience I will tell you a system will leak more under deep vacuum than under the same pressure. Don't ask me why, no explanation.

00t444e

You should pull a vacuum on it down to 29.9 for at least 30 minutes to get rid of all the moisture in the system, or down to 500 microns if you have a micron gauge. Then I like to let it set for awhile to see if it comes back up, if I have time I usually let it sit overnight, if it comes back up any then you have a leak somewhere.

PatHenry

Hahaha, Rambler, I appreciate the thoughts on the evaporater - if that's bad that's the one thing that will shut my project down since I'm not pulling my dash apart for AC. (If it were a heater core AND evap, that's a lot more likely, but so far the heat works great.. )
With the horrid temps and humidity the last week, it's a bit harder to say that AC is a luxury around here.

That said I'm taking this one step at a time and hopefully will end up with functional AC.

So status so far -- I oiled up the pump and hooked everything up. Following the instructions I started pulling vacuum. Unfortunately my in-line valve was not correct (it appears that one side is coarse and the other fine threads.. I should have paid more attention in the store today... grrr)

So the vacuum jumped up to -25-ish pretty quickly and there was a lot of smoke I wasn't prepared for.. but after checking my gauge connections and a microscopic tightening of the lines, the vacuum jumped to -30 and the pump sort of kicked down a bit.
I'm hoping that's a good sign. I'm about 30 min into vacuuming at this moment. After a good hour or so I'm going to close the manifold valves and hook the yellow hose up in "diagnostic" mode (closing the line in a loop from the looks of it) and then re-open the valves and theoretically that will let me read the vacuum without the pump on it. It's not as ideal as a valve (in theory I lose a bit of vacuum and get a little atmosphere in the loop line).

​​​​​​​If all goes well I'll hopefully be comfortable putting the grill back on and can look for a proper valve tomorrow.

PatHenry

So at least for the first 7 minutes or so there's zero drop in vacuum. I'll let it sit for a while and check again.

Fingers crossed.

PatHenry

Ok, so assuming the system holds vacuum when I check it tonight, what is my next step?

I lost a bit of oil out of the condenser when I replaced the o-ring. As I hadn't expected it, I obviously didn't catch it in a measurable way. A bit of Google research seems to indicate that the rule is 2oz per component. If I had to guess, I'd say the oil loss was probably around 2oz.
There was no oil when I removed the expansion valve or the Receiver/Dryer.

So do I pour a couple ounces of PAG 100 into the low pressure line and re-vacuum for a bit and then add R134a?

The sticker indicates 2lb (32oz) of refrigerant. Does this mean 24oz of freon + the 7.7oz of oil, or is the oil in addition to the freon?

XJThrottle

I didn't read your other threads...

32oz is the refrigerant charge only. Oil is not taken into account here.

2oz of oil would make a big mess if it all hit the ground. You likely only lost a few ML, not enough to worry about. If you can get some dye, add it before you charge the system. You can also buy cans of refer with dye in them. This will make up for lost oil. I would only get one can with dye, then the cheap ones with out dye to finish the charge. You will need three cans (12oz each) to fully charge your system.

PatHenry

You don't have to read the previous threads, I included them for reference - most of it the path of me going from knowing nothing about auto AC to where I am now.

It was definitely a fair amount of oil that came out. So it sounds like the "a little less than full" being better than "a little more than full" principle holds here?

​​​​​​​

XJThrottle

Too much oil is bad, so yes.