I have had my 91' 740 for 4 1/2 years and had to add R-12 for the first time from my stash I bought in the old days. I had to add because the pressure was too low to actuate the pressure switch on the receiver/dryer. My question is this: I added two 12 ounce cans and am wondering if I added about the right amount? I added the second can after the receiver dryer was just noticeably cooler. I am pleased with the operation, but know that the system can be hurt with too much R-12. Any guesses as to roughly how much should be added from not enough pressure to activate the switch to full? I took the car out for a ride and with the fan on full blast and all vents but the center one open and on recirculate, the temp was 38F. It was about 46F idling. The ambient was about 78F. Again, I'm very pleased about the operation but wonder if 24 ounces was too much R-12 to add. Thanks.

You're lucky you have a stash. My wife took the 965 in for an A/C check. It needed 3 OZ or R134a. Cold as all get out now. I had the system fixed last year. Added a VOV, Variable Orifice Valve.

I noticed R12 is 80 bux a pound.
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Warren Bain - '86 744Ti M46 >290Kmi, '99 V70Glt > 45K mi, '96 965 >100Kmi Wifemobile near Manassas Va.. Check the 700/900 FAQ via the 'features' pull down menu.

I'm always amazed when people continually top up their AC systems with refrigerant and then fry the compressor.

When your system leaked out (apparently at least 24oz of R12) the refrigerant it also leaked out at least a proportionate amount of compressor lube. Consider adding a few oz of lube..make sure you get the right kind for R12.

The vent temps are pretty decent. The accumulator bottle should be cold when the car is sitting at idle in those ambient temperatures. At cruise you should see between 33 and 40 from the vent, without the recirculating function turned on.

The system holds 38 or 40 ounces of refrigerant, which I'm not quite sure. Basically if you only added 24oz, it's possible you had 12oz or less in the system to begin with. Usually after one can it'll start to cycle on and off, but it'll mostly stay off. Based on that I'd say that you probably didn't overcharge the system. It could be still a few ounces undercharged.

The benefit of R12--and the downside of it's slow demise--is that it is less sensitive to pressure than is R134. That means, while 134 is only charged properly within + or - 2oz (depending on volume of system) R12 has a little more flexibility. You will probably be all right with that charge. The only way to find out the true answer, though, is to find out what the low and high sides are running in terms of pressure, in just about the ambient temperature conditions you've listed. That would give you the MOST accurate picture.


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1992 940 wagon, 72k
make people envious; smile often.

Glen,

My guess would be 24 oz. would not be enough to over fill a system that was low enough to trigger the pressure switch. But if you are really concerned ... find someone with a set of R-12 A/C gauges and check the operating pressures.