The AC in my 94 940 is working fine after adding a little more R-134a to deal with the Texas heat. But after reading the forums, I became concerned about the charge amount in the system. Outside of evacuating the system completely and adding the required 950 grams, is there pressure information available which would allow me to be more confident in the system charge?

The link in the FAQs to AirCondition.Com only provides vapor pressures for various refrigerants at ambient temperatures, not suction and discharge pressures of an operating system at various outside temperatues. There are scattered references to suction/discharge pressures at particular conditions (e.g. 85F outside temperature), but not a comprehensive chart like I have seen and used with other vehicles.

Thanks in advance!

Hi , if the ambient temp is 90F the static pressure in the system should be 104 psi. That means cold engine, not running. 70F= 70psi, 75F= 78psi, 80F=88psi, 85F=95psi. This applies both sides of the 49th parallel.

The discharge pressure of the full system will be approx 2.2 to 2.5x ambient temp. This is likely as per the web info you've read.

Unfortunately our cars are unique in that they mostly do not come with any ports on the high side (discharge side). Hence, volvo dealers will cahrge an empty vacuumed system by refriegernat weight. Of course this only works well asuuming the correct amount of oil is in there.

You can also take a best guess by monitoring the compressor clutch cycle... this is what I do. A low charged system that can still cycle the compressor will cycle it on/off very quickly, like every 3 seconds. As tyhe charge is brought up, the compressor will reach a point where it will run without stopping. Eventually, it should stop for a while and run maybe 60% of the time only, cyling maybe every 10 seconds. At this point, the charge should be maxed out. Careful not to overcharge, that will quickly kill the performance because it will bring up the low side pressure too high.

Just some advice, but of course the best is to fully evacuate and start over.

Thanks!
Greg Mustang
Montreal - Ottawa
Canada

that may be how it works in Canada, but down here in a Dallas summer, the compressor will often continuously run in 90-100 degree heat even with a correct charge.

When I charge from a can, I put a digital thermometer in the center dash vent, set the A/C to max cool, temp all the way low, set fan speed to middle speed, hood up, and add the R134a until I no longer get a temp drop at the dash. When it stops going lower, I stop adding freon.

DEWFPO
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1998 S90 070,050 and 1995 964 153,010