At 89 degrees, the compressor should be running all the time, at least at idle. I would add until the compressor stops cycling at idle-1000RPM, then leave it at that and do some road testing.

It is very normal for R134a systems to cycle on and off though, particularly when the cabin is already cool or the RPMs are high. It can cut out anytime the RPMs go up sharply.

You're right, this isn't the proper way to charge the system, but it's a (barely) effective way to use process of elimination to charge it. With R134a, the charge has to be correct or the system won't function properly. It's a far cry from the old days of "topping off" the R12 systems, which were a lot more forgiving. You may want to charge the remainder with dye-impregnated refrigerant so that you can figure out where it went, next time it needs a charge. At some point you should correct the leak, vacuum the system, and charge the right way. Recharging repeatedly will ultimately cause system failure as oil usually leaks out slowly with the refrigerant. But you probably already know this.

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Chris Herbst
Scottsdale, AZ

1992 940 153k
2005 S80 31k