bought a smaller 12oz can and added some more (about 1/3 of the can) into the system - up to 45-48 psi and holding.

 

Did you need some kind of adapter to connect the store bought recharge kit to the low side ? Don't have outside threads for the charge kit to screw onto ?

 

Figured out my issue.....lol...sorry to waste anyone's eyes on this one.

 

I bought an almost identical looking kit to the one GGG posted - Arctic Freeze 18oz. with gauge and hose at Harbor Freight - but my hose looks a little longer than the one pictured (not braggin'!) so I didn't need the extension.
The ambient temperature here in Houston was about 95F today (chilly for a July day here!) so I was looking for 50-55 lbs on the gauge. After running the car for a few minutes it read about 38 lbs before attaching the can. After pulling and holding the trigger and shaking several times it came up to 40 lbs but wouldn't go any higher. The AC is blowing colder so I stopped as I don't want to risk overcharging it. It feels like I used about half the can.
One thing I noticed that concerns me is that after removing the low side port cap I looked at the fitting with a flashlight (or maybe I should say 'torch' since it's a British car) and noticed a little bubbling which might mean it's leaking. After charging the system and removing the hose I looked again and it's not doing it anymore. We'll see how long it lasts. I used the same kit on my son's Ford over a year ago and it's still blowing cold so the leak stop formula seems to work.
Harbor Freight sells the Arctic Freeze for $30 but it's on sale now for $25 and after applying a 25% coupon from a magazine ad it was only $18.75.

 

That seems a very small pressure increase for half a can. I got mine from 5 to 32 psi with a full can at 65 deg. Possibly the bubbling you noticed from the low side port cap which suggests it wasn't initially closing properly could have given you a false start pressure reading?

A member with an X350 recently reported getting into all kinds of problems through overcharging so caution looks to be the best approach.

Graham

 

My system was cold but not as cold as I thought it should be. I added a full 12 oz Can and it got quite cold.

The change in Low Pressure was not Linear. The first few ounces increased the Pressure more than the Last Ounces.

I'm quite sure that I slightly overcharged it but am not going to change it since a little will probably leak out as time passes.

As Test Point's chart shows, the High Pressure changes much more with Ambient Temp and Charge Quantity than the Low Pressure does.

The Can gets very Cold, increasing the time required to add the charge. I used a Heat Gun that I bought from Harbor Freight to heat the Can.

The final low Pressure that I got with a ambient of 80 deg F was 45 psi at Idle RPM. (Lower with engine rev'd up).

 

When I was checking up on re-charging, I read that an A/C system in good condition can lose 3 - 5 psi each year.

This could explain why so many of us are having to top up when there's no evidence of leaks.

Graham

 

Actually, there is another twist to it;

The several replacements for 'Freon' (R22 for buildings and reefers, R12 for automotive), are:

A) Mixtures, not single-component. Bad news in that the components are generally not lost at the same rate. Vastly different molecular sizes.

B) Supplied/used with more than one 'tribe' of lubricants:

- Those compatible primarily with legacy seals (for conversion work),

- Those compatible only with NEW seal materials, for OEM and other all-new work,

- Those (allegedly) compatible with either.

C) The new refrigerants are not as effective as the Freons they replaced, so 'enhancers' - some of them dangerously flammable - are added to some aftermarket brands to claim advantages as to cooling.

Needless to say, the ratio of components can drift away from intended spec as folks attempt top-ups without evacuating, purging, drawing a good vacuum, and starting afresh with a charge and lubricant budget of known characteristics.

Most ESPECIALLY as not all of these components, least of all the lubricants and seals, are compatible, one with another.

Bottom line is that this gives rise to uncertainties on any system that has been touched by 'others' since new, and makes professional full-court-press evacuation, dryer replacement, etc more important than it was in the R12 days.

Can't really blame greedy dealers or third-party HVAC shops for that scenario.

Until EC and others already working towards follow-on replacement refrigerants (ozone hole is closing, BUT .. the new stuff is 40 times worse a 'greenhouse' gas pollutant than Freon ever was..and 1,400 times more so than CO2 - who'd ha' thunk it...)...come up with something more practical than uber-high pressure Nitrogen or CO2 itself ..

... it just is wot it is.

A mere interim band-aid - r1234yf - and a battle over it - reported here:

France deepens dispute over Mercedes sales ban | Reuters)

Some professionals won't even TOUCH a system suspected of previous amateur-level handling, either. Few want to be vacuuming alcohols, butane, propane or Sputniks through their expensive recovery gear, let alone risk contaminating otherwise-valuable salvage.

 

No one has mentioned it, but a decent probe-style thermometer placed into the coldest-available outlet is just as essential as the pressure-gauges.

Best-case is to drive the outlet temp down to right above freezing. I goal for 38-40 F. Usually measured only in the cool of an evening/early morning hours, with the circulating fan set on LOW and system in RECIRCULATE mode, air-flow-wise.

You will not see this on a HOT hot day, but not to forget that AC is ALSO essential to effective screen de-misting at cooler and uber-humid times.

It does one little good to ice-up the evaporator coils, have to switch-off and wait for them to thaw before AC is again useful - especially when failure to de-mist promptly and sustain that happy state makes vision uncertain.