Randy V

While adding refrigerant, do you run both the front and rear AC systems, or just the front one?

Speedtoys

If you fill it by weight, doesnt matter.

WSM does not say to..just depends HOW you fill it I suppose.

docmirror

Front and rear, both fans on high, check your recirc flap is open to the footwell.

dprantl

It will go faster if you have both front and rear on at full fan speed and the windows down.

Dan
'91 928GT S/C 475hp/460lb.ft

dr bob

Randy--

If you are charging from empty/evacuated or you know how much you need to add, it's way easier to charge with the engine off/cold and car cool. That way you can put the refrigerant in as liquid. Connect your charging hose as you normally would, but charge with the valve down so liquid is forced through the hose rather than vapor. If the system is less than 80º or so, you can wrap your hands around the can to warm it. Just a little heat from your hands will push the liquid into the system. If the system is warmer, you can hold the can in a bucket of tap-hot water for the same effect.

Once you start the car and get heat into the AC system, or if the car is running as you charge, you MUST charge with vapor. Putting liquid into the low-pressure hose to the compressor is inviting disaster, hydro-locking the compressor and scattering bits of it through the condenser.

Dan, I seldom dispute your advice, but I'll risk it now. Running fans at full speed with windows down means more demand (heat) is put on the evaporator. That actually increases system pressures and therefore slows the rate that refrigerant is drawn into a running system. My recommendation, especially if you are looking at the sight glass as a state-of-charge indicator, is to set the fans at 2 and engine at 1500-2000 RPM, typical operating conditions for most of us.

To the original question: Have the rear air on, second fan speed. Both front and rear temp settiongs at full cold.

~~~~

For grins, I turned the rear AC on yesterday just to make sure it still works. It does. Turned it off.

Randy V

I typically use a guage when filling - staying in the 'green' zone.

I fill with the can inverted.

Recirc flap? You mean have it in recirc mode - bottom slider all the way left?

Thanks, guys.

Bill Ball

Am I reading this correctly??? The auto parts store 134a kits with these "zone" gauges are intended for LOW SIDE use and you should NOT, NOT, NOT be filling the low side with the can inverted. Dr. Bob covered that.

dprantl

Yes, it is true that the pressure in the evaporator and condenser will be higher with the fan speed(s) at max with the windows down, although it somewhat depends on the efficiency of the condenser and fans. However, in systems that have a working anti-freeze switch, this is usually standard procedure. Otherwise the compressor will cut out repeatedly while charging. I suppose the fastest way would be to put the fan speed to '0' and bridge the anti-freeze switch . But, like you, I prefer charging by liquid on a cold car with the engine off.

And Bill is correct, if you are charging with the engine running, you MUST NOT connect a can to the high side and you MUST NOT invert a can of refrigerant when charging via the low side. You may be lucky and the liquid refrigerant does not leave the can fast enough and/or the refrigerant evaporates before reaching the compressor, but it is putting the compressor at risk of damage.

Dan
'91 928GT S/C 475hp/460lb.ft

rgs944

I just made the mistake of filling by sight glass with only the front AC running. I learned that you can not get it filled completely with the rear AC not circulating.

Rob Edwards

Engine off, system evacuated, inverted tank, charge with liquid, 1150 +/- 2 grams:

Randy V

I fill on the low side - the port located under the cowl cover on the later model cars.

I just added some freon to the BMW using the low side - I had the can inverted and didn't experience any problems. Maybe I was just lucky?

dprantl

Yes, you were. It is not worth the risk to invert the can and charge liquid via the low side with the system running.

Dan
'91 928GT S/C 475hp/460lb.ft

docmirror

Depending on the can/filler type, when the juice passes the orifice it acts kind of like an evaporating point where the pressure change causes the refrigerant to evaporate. Most people go slow with the little **** on the fill port, and that helps to evap the refrigerant as it leaves the can.

I'm still learning this stuff, but I just did three cars with help and none of them broke.

Speedtoys

Why have to help it, when you can just..well, not have to.

?

dprantl

Some people like to live dangerously I can tell you that I have seen/heard a compressor die due to it being charged liquid refrigerant, and it does not sound pretty.

Dan
'91 928GT S/C 475hp/460lb.ft