Not getting full vacuum
 

I am vacuuming my AC after reassembly and before I nitrogen purge it, using a HF 2 stage vacuum pump. My pump does not seem to want to reach a "full" vacuum (~30inHG), even with the manifold set disconnected from the car, relying on the quick connect seals. I've tried two manifold sets and they both agree. I tried changing the oil using fresh vacuum pump oil. I am getting to about 25inHg. I checked the local weather and we are at 30.12 inches pressure. Is this a normal reading or is it likely that my pump has failed? I have used this pump a few times before, and don't recall having any problems with getting the gauges bottomed out.
Sort of tempted to eat the cost and take it in to an indy to be filled on their machine. The local import shop is pretty pricey but there is a small shop that doesnt specialize and has pretty fair prices.

Describe how the manifold gauges and the 3 hoses were hooked up to the car/ vac pump and direct to vac pump . Include both valve positions. You have a leak somewhere.

I say don't take it to a shop, because you can't claim DIY anymore and you learn less.

Was the Nitrogen bottle ever hooked up to the manifold gauges? Nitrogen max pressure is around 2000 psi and if you're not careful with the regulator, you could have damaged the gauges by exceeding its pressure.

Right now I have the manifold disconnected from the car. I pulled vacuum for about 5 minutes with the low side valve open, high side valve closed, and both quick connects removed from the car. After looking more carefully I would say the gauge indicates about 27-28 atm vacuum. Once i had the vacuum established, and the needle no londer moved i shut the blue valve and let it sit for a few hours. No change.
Connected was the same procedure with the low side quick connect on the car.

99% sure it is not a leak. However my pump does make different noises depending on whether it is at max vacuum or not. Its more rattley when its still pumping down, then smooths out once its at or near max vacuum. Suspecting I may have got a dud pump.

When connected to the car while evacuating, both hoses must be hooked up to their respective fittings on the car, both valves on manifold must be open. It is normal for the vac pump to be rattling until full vacuum is reached, then it quiets down.

At the beginning of rattling, you should see a mist coming out of the exhaust. I think that is vacuum pump oil mist and is normal.

I will try it again with both lines hooked up. I didnt do that this last time, but I did with my other manifold set and got the same results.
At this point I don't really care to learn, I just want it done. The car has been off the road for about 4 months, except for one weekend when I drove it until the compressor split open. It should just need to be vacuumed, purged, vacuumed, and filled now. Once I get the dash back together that is.

On the compressor that blew up, did you evacuate/charge with only the low side hose hooked up? If so, that could explain why it blew up.

I still say finish the job yourself and not get a shop involved. You have all the tools needed. You are almost there.

Describe your charging procedure, I and others could go over it with you to make sure you got it right before doing it.

I have to ask. What's the technical reason for having the high side hooked up when vacuuming? Doesn't the TXV always always stay slightly open? If so, that would let the pressure equalize on both sides of the system. (Not trying to argue, I just am trying to learn if I'm misunderstanding how the system works)

I honestly don't remember how we vacuumed it last time, that was ~2 months ago.

I'll probably miss a step trying to go through this..

1. Vacuum system 30 minutes or more (low & high side open), check that it holds for at least 30 minutes.
2. Fill system with Nitrogen - check for leaks with soapy water, make sure it holds same pressure for several hours.
3. Vacuum system for 1hr, check again that it holds.
   EDIT
4. Close low side line, leave high side line open
5. Purge lines (my manifold has a shraeder valve on the yellow line)
6. Add first can with engine off, can upside down (using 12oz cans of r134a) into the high side of the system, working slowly
7. Close high side line.
8. Check for leaks with HF leak tester (can't hurt to look)
9. Run engine - 18" high power fan pointed at radiators, auxilliary fan jumped to run full time.
   END EDIT
10. Turn off car.
11. Check for leaks with UV light, soapy water
12. Disconnect can
13. Hook up fresh can
14. Purge lines again
15. Add second can, vapor only, can partially submerged in warm water. Watch pressures
16. Repeat for third can.
17. 4th can should be a partial fill to get proper pressures. (believe I figured ~37oz to get to 80% fill, may be slightly different since I have oversized condenser.

Any tips?

Probably going to try to take the vacuum pump back. Want to run one more test to make sure it can't achieve proper vacuum before I do. I think it's still under the 90 day warrantee.

Local indy that did the initial r134a recovery wants about 125$ to do the pull down and fill for me including their 134a. Thinking strongly about letting them do it. They should be able to fill by weight and not have to worry about purging between cans. I really feel like i have learned enough, and they have better equipment to do the job right. I havent been able to find anyone with equipment to do a nitrogen purge locally, so i may vacuum and pressure test with nitrogen before I give it to them.

Not really sure this answers my question about the TXV ever being completely closed, but here's an interesting read:
How Thermostatic Expansion Valves (TXV) Work - AC & Heating Connect

Have you tried another set of gauge hoses? Sometimes they can get a pinhole or one of the rubber seals can leak just enough to prevent perfect vacuum.

Yep, two different manifolds @ hoses. Same result

So manifold set A is not resetting to 0 when vented to atmosphere.
Manifold set B resets to zero, but has a poorly designed coupler to the vac pump on the yellow hose, wont let me tighten it properly.
Manifold set C is the gauges, red and blue lines from set A, with the yellow hose from set B.
I am getting roughly -.9 bar on manifold set C with the pump running connected to the car with both hoses hooked up. Going to let it run for 30 minutes, then close both valves, then turn off pump and see what it reads tomorrow. Also tried pulling down the manifold only, also getting about -.9bar.

I have checked all the fittings on the manifold and pump to ensure they are tight. The only other failure point that I see which might be leaking is the brass fitting on the compressor itself. It is tight though.

No receipt on vac pump, likely to just pay a shop at this point instead of buying more gear.

Here's the gauge after ~30 minutes of running the pump. I wish I had a better gauge for reading vacuum via the manifold, the graduations are a bit hard to read accurately in this scale.
http://www.peachparts.com/shopforum/...1&d=1474985289

With no leaks in the AC system or faults with the test equipment (manifold gauge set, vac pump), the gauge needle should be centered over the brass rivet= 30 in Hg on the gauge in less than 2 minutes of running the vac pump. If it was me, I'd be dying to find out what is going on and be trying different tests to determine the cause of the low vacuum reading.

I have been trying literally every test I can think of. At this point the only common point of failure is the vacuum pump itself, which I cant return unless I can find the receipt.
At this point I think I am planning on purging the system from the strongest vacuum I can achieve with my small nitrogen bottle, then bringing it to the shop to let them pull a better final vacuum and charge it.

What tests have you done? Have you verified your manifold gauge sets are bubble tight? I pressurized mine and put it under water up to the brass fittings of the gauge and found small/ slow bubbles in one of the hoses at the crimp ferrule.

The vacuum pump is unlikely to be bad since it is a new pump with fresh oil and it was good the last time you used it. Unless something was done to it that it does not like, such as using it to suck out remnants of the flush solvent, discharging high pressure into the inlet port.

Haven't tried submerging them under pressure. That's a good idea, if I can rig up something to hook them up to my compressor instead of wasting my limited supply of nitrogen. Mostly I've ensured that they hold a vacuum overnight. In my experience troubleshooting (and I do stuff like this for a living, though not in the mechanical field), the simplest solution is usually the most likely. In this case I have common ground that the vacuum pump will not pull a full vacuum against either manifold set. It's unlikely that both manifolds exhibit the exact same problem, so the simplest solution is the most likely, which means that the pump itself is probably bad. We are talking about a cheap pump here.

One thing I might try tonight is unscrewing the brass fitting from the pump (it's a Y fitting with two different threads). It's possible that part has a leak. It's also possible that the second fitting's cap is not sealing well. I might be able to replace that fitting, or find something else to cap the second fitting with. The last alternative is to try with a different pump. Conveniently there's a DIY repair place that has a pump that I can use without spending much. I just need to get the car on the road to take it by there.

I have perused many examples of AC system evacuation on the web and youtube videos that always had both hi/lo side hoses hooked up with both valves open during evacuation. Some sites says to remove both Schrader valve cores for faster/better evacuation since they are restrictions. I'd guess the TXV is a much bigger restriction than the Schrader valve cores and that is the reason you cannot achieve full vacuum with just the lo side hose connected and vac pump running for 1/2 hour. I experienced the same thing with my R4 system while vacuum/ pressure testing my system with just the lo side hose hooked up. I could not reach full vacuum (running the vac pup for at most an hour) and when I shut off the ball valve to cut the vac pump off, the digital vacuum gauge dropped slowly when it should be stable (if it did not have any leaks). Hooking up both hi/lo hoses while evacuating solved the "problems" I was experiencing with just the lo side hose hooked up.

Autozone rents out vacuum pumps for free. That's what I used for all the evacuations I have done. I have rented 3 different pumps from different stores just to see if one pump was different than the other 2. Two were used pumps and one was brand new one in the box. These are OEM brand single stage pumps and the quality is probably the same as your HF pump. One of the used pumps actually pulled a better vacuum than the new one per my digital pressure/vacuum gauge. Maybe the new pump needs to be broken in but I ended up using the old pump that pulled a better vacuum.

My digital pressure/vacuum gauge has a resolution of 0.001 MPa (0.29 in Hg) so I was able to see minute differences in vacuum/pressure levels that a Bourdan tube gauge could not.

Oh, I didnt know they rented them out! I will stop by tonight!

I've mentioned multiple times in threads you've participated in that I rent my vac pump from Autozone. I guess you missed that? SKU 90059-RAZ Call before you go, some Autozone's may not have them or have them but rented out already. Make sure there is oil in the site glass and ask them for oil if it doesn't. They probably want you to buy the oil but ask them if they really want you to run it without oil and they may give in and give you a bottle.

I don't memorize all of your threads, sorry. Also AutoZone's site won't navigate to the vacuum pump from their rental tool page, you need to search for it.

nearly ALL manifolds I've used SUCK! especially for displaying vacuum. the "compound" gauge has too much swing. a micron gauge is needed.

I have 2000.00 manifolds, with digital readouts, and full micron displays... junk!

I've come to the conclusion, that quality hoses, connected to a vacuum tree is the best way to get a quality vacuum...

but this is my JOB...

for the DIY... as long as the PURGE is done correctly, and the system is LEAK FREE UNDER PRESSURE... normal manifolds are fine for vacuum... but don't expect repeat use from them. expect worn readings, and such.

certainly leak test all the fittings, and connections, but on automotive, pulling a sub 1000 micron vacuum is fine to verify you are moisture free. weigh in the liquid on the HIGH SIDE ONLY!!! with the compressor OFF!!! and final charge on the low side with the compressor running.


as for why to pull from BOTH sides when vacuuming the system, it's because you want equal flow out both sides, with no impediments. the compressor valves will SERIOUSLY reduce the vacuum flow. pull from both sides.

Thanks vstech.
Got a pump from AutoZone. Will try it out after work. Even if I can get a good vacuum, going to let a shop do the fill on their machine, though i will need to be there to help with my modified electronics to make sure everything is running right.

I thought about the compressor's effect depending on the position of the stroke that it's in.

Youtube member Grayfurnaceman has some excellent videos on HVAC, much of it applicable to MVAC. I recall one episode where he says the best vacuum is pulled when the vacuum pump is connected to the system being evacuated with copper pipes, no hoses.

Yup. Copper is best. All rubber passes some.

As for compressor stroke... valves open when pressure pushes them open. If comp isnt running, valves are closed.

You don't trust yourself doing the fill? Is the system filled with oil already? Does the shop use virgin R134a or reclaimed? I would suggest not use them if reclaimed. What if the shop does the fill and the vent temps do not meet expectations? Who would you blame?

In this case, we are talking vacuum, not pressure. What does the reed valves do under vacuum? I really thought (though I am not sure) that the effect I was seeing has more to do with the compressor and not the TXV. The effect was that when I shut off vacuum to the system (with a bubble tight ball valve) that was evacuated from just the lo side port , the vacuum level in the system immediately drops slowly in a tight system with no leaks.

I have a manifold set, which has already been noted to not be very accurate. I have 12oz cans instead of a tank, which makes filling by weight accurately difficult. I also have no experience except for supposedy causing my compressor to split in half.

Not sure about whether they use fresh r134a or recovered. Will be sure to ask them
May call a mb indy to see what they would charge, they did a recovery for me at one point and creditted me with the r134a they recovered. Not sure if they would be willing to use fresh, even if I supplied them with the cans.

And if they cant get the vent temp right, what makes you think I can? Every single thing I have done has been nitpicked, so why should I be confident in my skills at this point?

You are a funny dude. You call my asking questions nitpicking and that I took your confidence away. If I didn't ask the questions, we would not have learned that you may have evacuated wrong and not gotten all the flush agent or moisture out, and that may have been the cause of the compressor blowing up.

As to whether a shop can fill your system with the correct amount of refrigerant, they may or may not be able to since your system is no longer stock by changing to a parallel flow condenser, which may have increased or decreased the total system volume. I have mentioned that in your other thread and suggested you measure the volume of the new condenser vs the old. That may not be easily done so I also suggested that you ask the vendor of your parallel flow condenser if any +/- adjustment of the refrigerant should be made. The 2.9 lbs of R12 and whatever the equivalent in R134a may not be correct anymore so you or the shop will have to charge by feel, not by weight.

The manual for the Condenser calls for 80-90% by weight of the r12 amount. Obviously some of it will have to be done by feel. However, clearly I'm not experienced enough to "feel" it.
Just whatever, it's my money, my car, and my decision.

Want to give the junk to me? I'll gladly take them off your hands!
ps. Is 2000.00 the model number or the price in dollars?

Got the AutoZone vac pump last night. Apparently you're right Funola, the problem is with my manifold(s). That or I got two pumps with the same issue (the HF one and the AZ one) - getting the same reading. I let the AZ one pull down for at least an hour last night, no change in the gauges. I guess I could borrow a manifold from AZ also.

I did however leave the car pulled down overnight to the max the pump would achieve (~85-90%) and it held that same pressure, so hopefully I don't have any massive leaks in the system Tonight I'll probably pressurize it with nitrogen (hopefully will get ~150psi out of my small tank), then I'll try to get an appointment to get it charged. I think I'm going to the indy here that primarily focuses on MB and BMW.

With mechanical gauges, I find it easier to not go by the scale numbers. Instead, cut a pointer out of masking tape and point it at the gauge needle. Any movement in the needle will be more discernible.

Good tip. I will try that when I pressurize it. Thanks

The step "Add first can with engine off, can upside down" is incorrect and may slug the compressor with liquid refrigerant since in a previous step, the low side valve was open with engine off. Liquid should only be introduced into the high side port with engine off in most cases. It could be introduced into the low side with compressor running if you can control the rate it is being injected (i.e. slowly, using the valves on the can and the low side manifold valve). I'd also skip the step "shut of engine to check for leaks with UV light, soapy water" in the middle of charging, since there should be no leaks at this point, from the leak tests already done prior to charging.

Here is a very good charging procedure:
Basic Charging Procedures

I still think you should charge it yourself. I think you can do a more careful job than a shop. You have all the equipment necessary. Just write down all the steps, take your time and check each step off as you do them. That is how I did mine so I do not make any mistakes. There's lot's going on and can be confusing if you don't do this stuff on a daily basis.

If you insist on going to a shop, pick the shop that use virgin R134a, not reclaimed, the shop with the best equipment and know how in AC work, not general Mercedes or BMW know how.

Thanks funola, I will correct that liquid into lowside mistake in the future. I must have misread that. Ill also update that post so people dont follow my mistakes.
I may see if they can use the r134 cans i have my transferring it to their machine.
I will look around for other shops locally that specialize in ac work rather than MB specialists, thats a good point

They cannot transfer your R134a cans into their virgin R134a tank, which has one way valve to prevent such tactics. You do not want them to transfer your R134a cans into their reclaim tank for obvious reasons. So the only option is to charge direct from your cans or from their virgin tank if you want to be sure you get pure R134a, and not potentially contaminated stuff.

Yeah - I called one shop that has fresh DuPont Suva just now and the proper equipment. It would be a bit more since I don't have a credit for recovered r134a with them, but it's probably worth it. I'll call the MB specialist back later to see if they can run fresh r134a for me as well. I think my system was actually a little overcharged when I had them drain it, so I should be able to get it charged without paying for the refrigerant, unless they want a little extra for fresh stuff.

OR i can try it myself, but it's too cool out here now to really trust vent temps, and I don't know of any accurate way to weigh it from cans. Maybe I'll shop around for a small tank.

Any idea of the availability of say a 5 pound tank of r134a? I am crazy tight on storage space in my garage, so a 30lb tank would be excessive - plus my digital scale won't read that amount.

Interesting that you say it was overcharged when the shop reclaimed your 134a. I recall you said you had trouble getting the 2nd or 3rd can in when you did the charging. The question is what was it overcharged with? Obviously not R134a?

Hey, I am not nit picking at you. Just trying to understand what happened.

That was at a later attempt...
Long story but..

Bought car - AC worked but only on cooler days (so i'd get near freezing vent temps, but only at ~70deg f, leaked at TXV, thought "oh, i'll try to charge it with a little leak stop" (yeah, that was stupid). Topped it off, tried to get the low side pressure to match chart, overfilled it)

Had the MB shop reclaim it for me, got credit for amount (not sure how much, need to look for my receipt or have them find their copy)

Second fill: Replaced TXV, drier, added a little oil. Tried to charge at DIY repair shop with the owner helping - could not get system to accept more than 1 can of r134a
Had different indy shop drain what little we got in the system

Third fill: Flushed everything extensively (found at least 2 likely clogs - probably from the leak stop I added). Replaced TXV, drier, one of the lines to the evap, and swapped to parallel flow evap. Filled to 3 cans of r134a, but had slightly high pressures. Compressor ker-ploded. I'm still curious if I have some clogs in my old evap, haven't leak-tested it yet to see if it's salvageable.

Fourth fill: Decided i'd had enough of this, replaced entire system, Sanden compressor, new PF evap (again), new hoses, new aux fan, etc. Determining how to have it charged/charge it myself at this point.

Why is it so important to charge by weight, especially if you are not sure what it should be exactly? If you have 12 oz cans, put all 3 cans in and you have 36 oz, which is 80% of 46 oz (2.9 lb) of R12. See what vent temps and pressures are with 36 oz and adjust up with the 4th can if necessary.

Won't I lose some to the lines each time I change cans, and risk letting air in?

No air gets in if you purge the yellow line after connecting a can. You won't lose much (0.01% of total is my guess) if you purge for 1/3 of a second as vapor. You'll lose more than that when you disconnect an empty can than purging for 1/3 sec. To get the most out of a near empty can, invert the can and get it out as a liquid. Do that slowly (a little at a time, like 1 oz/ minute) so you don't slug the compressor with a liquid.

Okay, that seems reasonable. I'd need 3 cans of r134a, plus possibly a small amount from a 4th. Here's where I'm at

Downsides to filling it myself:
Filling by vent temp may be difficult this late in the season. It's looking like we're going to be around 78F for the next few days and likely wont get much warmer until spring.

I'm still not convinced my equipment is up to par. I've tried getting a vacuum with both my HF 2-stage pump and an AZ 1-stage pump. Both are reading about a 90% vacuum on both of my manifolds. (One manifold is not zeroing out, so I trust it even less than the other)

Both gauges on my better manifold agree with each other, neither is saying that the vacuum is 100%. Either the pump or manifold has a problem. (I get the same results with the manifolds on the car vs off the car)

If I mess this up and overcharge the system, introduce air, or cause it to fail in some other creative way, at the minimum I am out 100$ for a new condenser, some amount to have the system evacuated properly if it's not a complete failure, as well as around 100$ in oil/antifreeze/atf to swap the condenser - there's no way I can swap condensers with the radiator assembly in place. (Unless I try to save the fluids to reuse). I'd also need to flush the system, replace the drier, and pull the compressor to change the oil. The Sanden Compressor kit I have is more difficult to install than the original R4.

The last time I tried this, my system failed and filled my house with r134a vapors and oil. I'll need to find somewhere else to work outside to avoid any possibility of having this happening again.

However, if I pay a shop:

They have higher quality equipment than me. They can probably pull a stronger vacuum and/or measure it more accurately. There should be little room for error, since they can specify an amount of refrigerant to add.
They may have a better sniffer than I do to check for leaks during the fill process.

They are much more experienced than me.

The money to pay them to fill the system is fairly insignificant compared to the money I've spent on the system to this point. (~5-10% of the total system cost, depending on which shop I go to)

I get to sit around and read magazines for a couple hours while they do the work (huge benefit to me at this point, I'm tired of messing with it). If I go to the MB specialist (well, more of a european specialist) I get to look at other cars that I can't afford. Last time they had a XJS 12 Convertible..

I will hopefully get to learn a bit by watching them, since they may need my help with the electronics I've modified.

Don't you want to find out why you can only pull 90% vacuum, even if you are bringing it to a shop? I'd buy a manifold gauge set from HF to see what it reads.

What's the results of the Nitrogen pressure test?

Per this article https://macsworldwide.wordpress.com/2010/08/24/mobile-ac-system-contamination/ air is the most common contaminant in recovered refrigerants.

I have a manifold set from HF. It also does not read properly. I dont really see a point in buying a third manifold. Either both pumps are bad or both manifolds are bad.