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kuehl kuehl is offline
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Join Date: Aug 2004
Location: Stuck in NJ
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Originally Posted by adias View Post
What is the criteria to recharge? Blow temp at the AC vents at what temp?
In the R12 factory design, the drier had a floating ball in a view glass, although not accurate it kinda gave a measure. With R134a site glasses don't give an accurate reading.

You can't go by vent temp because there are a dozen issues that cause vent temps to seem higher than normal. Say for example you had made observations after you had a perfect charge, maybe 85 ambient, vehicle in the shade, windows up, thermostat max cold, center vent temp 44F at evap fan speed 1. A year later its 95 ambient and your car was sitting in the sun for 5 hours heat soaked and you are feeling the vent temp at fan speed 3. An iced up evap core will have higher temps. A failed front condenser blower motor can cause high temps. Keeping the engine deck lid up (no air flow through the condenser coil) will cause high temps. A broken evaporator outlet air tube will cause high temps.

Best to go by pressures in the system.

Assume you knew you had a good factory charge; you just has the system serviced, everything was documented:
the ambient temp that day, low and high side pressures at idle, amount of refrigerant,
and a 'static' reading after the system had been turned off and the system pressures equalized (low side and high side are the same). If they documented the static, say for example: R134a, 90F, 114 psi. or whatever. You could use that as datum to determine if your system was near full charge same way it was the last time it was properly serviced. Compressor clutch not engaged, etc.

Ditto pretty much all of above in static, however, this time the system is running and you documented everything when the system was last properly charged. You compare apples to apples: pressures, ambients, etc.
1987 911 cab, modified

Last edited by kuehl; 06-12-2019 at 09:38 AM..
Old 06-12-2019, 08:58 AM
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