Re: Too little R134a! - Saab NG900 & OG9-3 Bulletin Board - Saabnet.com
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Re: Too little R134a!
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Posted by PeteM (more from PeteM) on Sat, 23 Jul 2005 21:13:51 Share Post by Email
In Reply to: Re: Too little R134a!, kyle morley, Sat, 23 Jul 2005 16:35:25
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AFAIK, the fluctuation in the low side pressure is caused by the compressor running intermittently, while the AC is on. On my car, the fan cycles more-or-less along with the compressor, and you can actually hear the click from the magnetic clutch when it engages, as well as see it spin if you shine a strong light down toward the compressor pulley.

The pressure goes down as the compressor starts to pump refrigerant from the low-pressure into the high-pressure line and from there into the condenser, and then reservoir/drier. When the clutch disengages and the compressor stops, the pressure starts to equalize between the high and low sides of the system, and low-side pressure rises until the compressor engages again. That accounts for the up and down fluctuation when the temp is not on the lowest setting, and makes a psi measurement more difficult.

If I set the system on "LO" via the ACC controls, after a few minutes my low side pressure is stable. If yours is not, then something else may be wrong.

I could make a guess, and say that IF the electric fan is cycling and not providing air flow over the condenser, then the condenser will not do its job 100% and that MIGHT make the pressure fluctuate... but I have not seen that happen on my car.

posted by 69.212.1...

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