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Old 08-05-2008, 02:09 PM
777funk's Avatar
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Correct R134a Pressure at 2k RPMS???

I just checked the low side pressure on my Father in Law's 2004 Buick LeSabre (R134). It read 62PSI when reved and held at 2000 RPMs. The ambient temperature is approx. 105F here today. At idle he was about 10-15PSI higher than that. His A/C was recently charged by the dealership.

I just converted my w124 300d to 134a and I'm at around 40-45PSI at 2k RPMs.

Is this right for the ambient temp of 105F? Will it hurt to go higher (i.e. 62 PSI like my father in law's Buick)?

I noticed that my compressor clicks on and off pretty quickly if I go higher than 45PSI.

I'm not at all an A/C pro. I took the car to a shop to have the system pulled with a vacuum for 45 minutes before charging. I converted to 134a last year when changing the compressor.

Just looking for a few tips before we head out on an 8 hour trip. Cold air would be nice!

Last, has anyone compared Freeze 12 to plain old 134a?

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Old 08-05-2008, 02:31 PM
Scott98's Avatar
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Join Date: Aug 2003
Location: Weston, FL
Posts: 1,254
I'm no A/C guru so hopefully some more experienced members will chime in. What your low side pressure is indicating, is the pressure of the refrigerant by the evaporator. If you know the pressure of refrigerant, you know its corresponding temperature simply by looking at the pressure/temperature chart for that refrigerant. That is what the pressure is telling you, not the amount of refrigerant in a system.

Ideally, you'd like a low side pressure of about 27psi with R-134 at the evaporator. That means your evaporator temp will be slightly above freezing. The hotter it is outside, however, the harder it is for heat transfer to take place so your low side pressures will generally be higher as outside air temperatures increase.

Remember, a 30 pound container of refrigerant will show the same pressure at any given temperature whether it has 30 lbs of refrigerant in it or just 1 pound. The same is basically true for your car.

A/C work can be complicated and dangerous. Its best to leave it to a professional unless you really take the time to learn.

Good luck.

1982 Mercedes 240D, 4 speed, 275,000
1988 Porsche 944 Turbo S (70,000)
1987 Porsche 911 Coupe 109,000 (sold)
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1985 Mercedes 300D 227,000 (totaled by inattentive driver with no insurance!)
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Old 08-05-2008, 02:38 PM
rrgrassi's Avatar
mmmmmm Diesel...
Join Date: Jun 2006
Location: Royse City Tx
Posts: 5,122
ACkits has a temp/pressure chart. Freeze-12 cools better the R134. R12 cools the best.


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06 VW Jetta TDI 133K miles-replaced the other '06 that quit after 300k miles. (did not catch the bad cam in time)

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 195K

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