How to DIY filling A/C?

850 gram of 134a is what I have been using both for the 308 and 512BBi. Overfilling will reduce the performance.

Best, Peter

 

That's not strictly correct. Sight glasses were and are used as a service aid on many systems apart from R12 . They're now not as common on smaller systems; to cut down on cost, reduce the potential for leaks, plus in modern cars the position of receivers often means you cant see them or they're built into the condenser. R134a condenses to a liquid just like R12. The liquid line that feeds the expansion valve, so called as it should be full of sub cooled liquid, should be free from refrigerant vapour, and this is so the expansion valve can work at its best. Expansion valves control by superheat, which controls evaporator capacity. The sight glass is indicating whether or not the liquid line is full.
However you charge these systems, it is well worth validating the charge by superheat measurement, and you should then know how hard the evaporator is working. These systems are pretty wheezy to start with and with these measurements you could also determine the best course of action for a system upgrade......

 

Good luck Martin! I became a reasonably competent AC tech NOT because I really wanted to but because three different AC shops I took my 328 to made the AC worse each time! I decided that the only way to get it right was to learn to do it myself!

FWIW, the last of the so-called AC shops overfilled the system to the point the compressor immediately locked up when switched on. The tech then said I needed a new compressor since it couldn't handle the "1/2 pound of extra refrigerant" he added to "make sure it cooled really well!" I asked him to remove that extra 1/2 pound and the compressor then worked OK. I drove home in disgust (three's a charm) and began studying auto AC/obtained the gauges/vac pump, etc and have done all my own AC work since.

Re sight gauges- There is a lot of information available re sight glasses/R134. For those that are not sure either way, do some searching and then make your own decision about using the sight glass to determine refrigerant charge. As I say about virtually everything, do the research and then do whatever you are comfortable doing.

Example, I use propane-based refrigerant in my 328; others are not comfortable doing that.

 

Plus you can go to lengths that are not economically feasible for a commercial shop.

For example, a shop may pull a vacuum on the system for a couple of hours and consider the system sufficiently leak-free. At home, I pressurize the system to 100 psi with nitrogen for 48 hours. On the BMW, the last leak I had to hunt down was 1/2 psi per day at 100 psi. (The stupid car had 5 leaks.) (Yes, ambient temperature variation was accommodated in the measurements.)

 

I had my 308 recharged with R134a by an mobile A/C guy and it only stayed cold for 3 months . After a bit of research I bought a vacuum pump and gauges replaced the receiver dryer and added a little air con oil then recharged with one 425gr can of hychill minus 30 gas. It has been 10 months and the A/C still blows cold.

https://hychill.com.au/en/products/minus-30

Minus 30 is a blend of R600a and R290, two naturally occurring hydrocarbon refrigerant gases and is perfect for use in automotive air-conditioning systems and in refrigeration applications.

• Operates at lower pressures to R134A
• Similar volumetric refrigerating effect to R12 and R134A
• Can be used in a R12 or R134A compressor or a specific hydrocarbon compressor
• Can be used with R12 or R134A heat exchangers & expansion devices
• Compatible with most common refrigeration materials and lubricants

 

I've been using Duracool - another hydrocarbon refrigerant - for many years. I agree it works great - slightly better cooling efficiency than R12 and far better than R134. (Well...the refrigerant works great but the 328 AC remains, at best, fair).

However, be aware that none of the hydrocarbon refrigerants are approved for use in vehicles in the USA (yet). Can't speak for other countries. That makes it totally a DIY thing. If you use it you should stick an appropriate label in some visible location to prevent a shop or private individual from contaminating 'legal' refrigerants if they were to work on the system and evacuate the refrigerant.

 

Martin
I've done mine several times as I remove the AC compressor when I have to pull the front cam cover.
Several years ago I converted to R134 with no problems. I didn't change anything in fact the first time I did it I didn't even pull a vacuum on the system. It always worked great with AC temp around 50 - 55 degrees on the hottest days in traffic.

I just refilled again (2nd time in two months due to my error with front crank seal).

So here's the steps.

1. Get r134 from Ebay. Not a problem in US.
2. Get adapter that screws onto can with gauge.
3. You will need and R12 to R134 adapter for the low pressure fitting on the compressor.

This time I did the following.
1. Changed all O rings from black to green. (got them from Harbor Freight) People say the black O rings will deteriorate over time but I actually never had any problems.
2. Changed oil in compressor (original) to ESTER oil. Apparently important as there can be a chemical reaction with the original type oil (mineral ?).
3 Pulled vacuum on system and left overnight it insure no leaks and probably helps gen moisture and such out.
4. Hooked up charging adapter to low pressure side of compressor.
5. Screwed can of R134 to adapter which punctures can.
6. Filled with 1st can without engine running.
7. Started engine, turned on AC and filled until gauge reads green. (AC may not "click" on until enough pressure)

I haven't changed anything in the system except the O rings, Compressor oil and R12 to R134.

One thing I did discover, which may be just my 40+ year old system, is that its very pressure sensitive. If it builds to much pressure it will "click off". I've had to bleed some pressure off to keep this from happening. You can hear the AC clutch kick off if the pressure builds to much.

I have a full set of AC gauges that I use for my home AC unit that will work but the cheap adapter works fine for me.

Best of luck
Barry



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