r134. 90 degrees=105psi. as long at this was not a can that was in hot water.
let the system sit over night and check resting pressures again.

2 cans was not far from what you needed in there. also depends on engine RPM. check pressures at around 1500rpm, windows closed, fan on hi and recirculate.
hi was a bit hi but I don't think so for these cars. condenser area is still small and air flow is poor.
notice your low side went up on the 3rd can. but still depends on RPM.

you don't need a fancy system to purge the lines.
after connecting the new can, burp the line at the gauges.
if you feel the need to go the extra step, connect the new can, don't puncture it yet. open the low side gauge then burp the line to the can. close the low side. puncture can then burp the line at the gauge. then fill.


how much oil did you put in the system?
kuel will know better than me if too much will cause this problem of low vent temps.

you may try driving it a few days and see what it does.

I know kuel does not like this but I leave the deck lid open and put a box fan on the rear deck lid on low. pressures will go down when driving due to better air flow and higher engine RPM.

24 oz will be undercharged ("and add'l condenser with fan."); I'd guess by 33%

Based on the system pressures with 12 oz report in the original post, and running pressures (as stated before)... system has signs of atmosphere (air in the system).

Ok...thinking of getting a micron vacuum gauge...that would tell me if I've still got ambient air in the system....correct? Looking at the Robinair RAVG-1.

so at this point you may look for a shop to charge and check the system.
I charge $70 plus freon, dye and oil, and you will get my 33 years of experience in automotive ac.
and if it goes flat I will check it over with the UV light as part of my ac service.

A micron gauge is more accurate than a typical analog low side gauge. It can help you with testing your pump, your manifold and service set, verifying system leakage rates, and determining system's vacuum level more precisely. However, it won't tell you if you have air in the system, it only conveys the level of vacuum in a different scale.

There are a many brands of micron gauges out there, from simple inexpensive units expressing the level with led's to units with lcd displays. In selecting a brand you just have to take in all the factors: price, warranty, tech support, number of times per year you will use it, ease of use, etc. I have 3 hanging around the shop, each is like a character in a novel.

UV dye will not expose leaks that lack refrigerant oil weeping from the source. Visual tools, such as UV dye tracers or soap and bubbles are limited to working in areas where you can see. Electronic leak detectors, such as a common heated diode type, are the preferred tool for pin pointing leaks; but they are limited to their ppm sensitivity, meaning ....you won't detect low permeation rates in old non barrier hoses.

88911coupe, still has the problem of getting the car, vac and charged correctly
so dye and sniffers do not come into play yet

If he is following good procedures and can't pull down a good vacuum, and his pump is doing a good job, he will need to find the source of the leak, hence a shot of R134a in the system, gauge and manifold set, and then use an electronic leak detector.
Just went through this with a brand new electronic manifold. The micron sensor was defective; leaking.

if he was close
I would hook him up

Hoping the micron gauge will help me confirm my vacuum's pulling a vacuum...I'm 99% sure it is but this way I'll be able to confirm. As Griff has pointed out, it looks like I've got ambient air in the system so at least this way I'll be able to determine if its something I'm doing wrong in the re charge.

I agree a micron gauge will not tell you that you have ambient air in the system. But is can be used to ensure the system is tight and that moisture has been evacuated from the system.

JB Industries has a good technical paper on Deep Vacuum, Its Principles and Application.

I used a BluVac Digital Vacuum Gauge for evacuation of my system.

BluVac Manual

Offer is still open to assist in sorting this out. I know last time I offered, you were thinking of taking it to an AC shop, but looks like you're still fighting this on your own. I don't have a leak detector, but I've got a working Vac pump, gauges, and also a Dry nitrogen tank we can use to pressure test the system for leaks.

OK...got the gauge and tested it today...going to be 100 here in Dallas. I just used a single hose hooked up to the gauge to remove as many variables for leaks. This was with oil left over from last vacuum pull, not fresh. Immediately dropped to about 4,000 and stayed, no further, then i snugged up the gauge threaded into the T fitting and each small turn (10 degrees maybe) it would drop again. Once it got to about 1850 microns it stayed there. Thats no where good enough is it? Next test it to put fresh vacuum pump oil in and see if it will go lower.

Buck, my personal opinion is that you are not doing the procedures correctly. There are some real good threads here that are easy to follow carefully. This is not really that difficult if you do each step carefully and thoughtfully. This is a good one.

http://forums.pelicanparts.com/porsche-911-technical-forum/834136-my-ac-burns-me-up-summary-fix.html

Show us some pics of your equipment and your hookups for a start to help us get you thru this.

Just to clarify the test I just did was not hooked up to the ac system, it was just the hose hooked up to the pump and micron gauge. Basically just wanted to see what the vacuum pump can do.

A good pump should be able to pull down to about 40 microns (29.915"). Was the charging manifold (gauges) attached to the vacuum micron gauge?

Could be improper oil level in the pump. Too high or low some pumps are fussy about that.

When was the last time you changed the oil on the pump?
Change the oil after each use.

The "ideal" vacuum of 500 microns on the system is a good indicator that the system does not have any leaks. On a 911 ac system with what seems like miles of hose will be difficult to get that low. Refrigeration oil in the system and the hoses out gassing plus residual refrigerant you would probably be lucky to hit 700-800 microns on a new clean system. YMMV

Interesting tidbit of info (maybe!) that at 500 microns, the pressure in inches of mercury is 29.90. Pretty close to a pure vacuum!

Your measurement of 1850 Microns at the pump would be about 29.85" hg gauge.
29.90 and 29.85" would be pretty difficult to see with the compound low side gauge.

I am not a huge fan of leak testing a system using a vacuum. Leaks allow air and moisture into the system and some types of refrigeration oil is highly hygroscopic and will absorb the moisture from the air.

Try to isolate your equipment problem to pump, hoses or manifold and see if you can get that pump to perform.

Update to the update...I added teflon tape to the threads on the gauge and now am getting down to around 380 microns. This is not new oil, just wanting to see how it worked just hooked up to the pump. Next I'll put new oil in and see what I can achieve in a real test.

ideal is 500 microns.
I have done this on my brothers 930. I never got 500 and each time he said just charge it. I did and it all leaked out.
no need to change oil. 380 is good.

I agree,. leak testing with vacuum os not good but we all do it/have done it as needed. nitrogen is best. charge it and see if it holds. also charge it then vacuum and repeat is best way to remove moisture. I have heard nitrogen is not good for 134 systems(?). I still used it on my 930. found a leak at the condenser but still have not fixed it.

if you cant reach 500, leave everything connected, turn off the pump and see if the micron gauge holds. if you get it down to say 1000 microns and it will hold it for a few days with the pump off I would charge it.

these are very large systems with a lot of places for leaks.

Found this...year later and same problem. Last week pulled vacuum and saw no leaks overnight, then did recharge using a hose set up that allowed to to vacuum out recharge hose between cans. Still same problem, getting 40 Psi on low side and low 300's on high side after just 2 12 oz. cans and vent temps only about 60 degrees. Decided to take it to old, respected AC shop here in Dallas (McCains) to see if I'm doing something wrong. I did not evacuate/vacuum it before I took it to them. The pulled out the r134 and vacuumed it down then put about 44 oz of R134 and got same results as me....42 psi on low side and vent temps about 60 degrees. The foreman did say he thought air had been in system but said they "purge" it before recharging to make sure no air in system. I told him there are guys with set ups similar to mine getting vent temps in the 30s so he's as confused as me. Not sure what to do now other than just accept the poor performing system. With all the enhancements I've done I was expecting better results.

Best way to test your service manifold and service hose set is to pull a vacuum on an empty 30 lb refrigerant can. Ideally you want a 4 valve 4 hose service manifold: low side, vacuum, refrigerant and high side. Pull down to say 200 microns if you can. Close your vacuum valve. Don't be surprised to see the micron level rise to 500 microns within a minute or so, then it should level out.

"40 Psi on low side and low 300's on high side after just 2 12 oz. cans and vent temps only about 60 degrees."
At what ambient air temperature around the car?
Was the rear deck lid down resting on the service hoses?
Is the front condenser blower motor running?

"They pulled out the r134 and vacuumed it down then put about 44 oz of R134 and got same results as me....42 psi on low side and vent temps about 60 degrees."
42 psi on low suggests an evaporator temperature of 47 degrees. A delta of 13 F degrees between the vent and evap core .
Stick a digital thermometer in the evap core to observe what its temperature is.
In general terms, with a normal operating system your evaporator outlet hose fitting will be sweating or frosted on a good system.
If your evaporator core is near freezing and you are seeing much higher vent temps then inspect for air leaks between the plastic evaporator outlet tube and the center vent.

Buck, according to a Sanden troubleshooting chart that I find useful, when both high and low sides are high, it typically means insufficient condenser airflow and/or an expansion valve that is not working properly (or its intake screen is somewhat plugged - it it has one of those).

Of course, you don't really need a chart when you've got Griff posting here, but it does come in handy, and breaks down the basics of how mobile a/c systems work.

https://www.sanden.com/objects/SANDEN_SYSTEM_DIAGNOSIS_CHART.pdf