Re: [E36M3] a/c re-charge

[alex.fadeev@xxxxxxxxxxx]

bmwm3nut@domain.elided wrote:
>
> now that the a/c debate is on, have anyone tried those R-
> 134 re-charge kits from Wallymart or Pepboz? I brought a
> kit that has the pressure gauge, line, and refrigerant.
> I wonder what the pressure should be for our systems. I
> see small amount of bubbles while I am idling and thats
> a bad sign. My a/c sucks while idling. It goes down to
> 45 deg. when moving but goes to 60 when idling!!!.

Tim,
As my experience showed, having properly calibrated gauges is 1/2 the job.
The ones my friend had borrowed from AutoZone must have been dropped one
too many times. They were showing that my system was mildly overcharged
while in fact it was way low. Good gauges sell for north of $100.
As far as your problem goes, which car are you trouble shooting?
Most compressors are designed to run at the max duty cycle with RPMs north
of 2K. That way the compressor would not over pressurize the system on the
highway. So right off the design board the AC system will underperform at
idle. Some cars are better at idle cooling than others. E30 M3s are rumored
to be among the worst.
The TIS lists proper E30 AC inlet pressure range of 1.0-2.2 bar (14.5 -
32.0 psi) and outlet pressure range of 12-22 bar (174-320). All at +20 to
+40C ambient. The measurements should be taken with the RPMs held steady at
2000 for 5-10 seconds allowing the system to stabilize at the optimal
range. Now set the HVAC speed at 1 and direct all air to the face level
center vents. Stick a thermometer in them and on a humid 90+F day we got
the vent temperature of 41F. At idle the vent temp would slowly climb back
to about 48F. It took some unscientific bumping of the pressure up and down
to get the coldest air vent temps. By the time we were done charging my '89
325i the inlet was exactly at 20 psi and the outlet at 200 psi under the
above described conditions.
My wrench mentioned that R134a system will run at slightly higher outlet
and lower inlet pressures since R134a requires higher pressure delta to
provide optimal cooling.

HTH,
alex f

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