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HIGH Bouncing - Blockage?

mikes603 on Mon April 27, 2015 7:26 PM User is offline

Here's a video of a Mini Cooper R53 (new owner) running with an AC manifold attached. Notice the High side bounces from 150 to 250psi in a cycle with the fan kicking on. Low side wanders around 30psi. Shop was at 60degF

Does this indicate a blockage at the expansion valve? Or is there a non-condensible in the system?

AC blows cold but not freezing cold. Maybe 50degF (I need to put a probe in a vent still).

HECAT on Tue April 28, 2015 7:45 AM User is offline

Fan kicks on, removes heat from condenser, high side pressure drops; this is how it works. I see no correlation to think expansion valve. You can test for non-condensable with a refrigerant analyzer, or evacuate and recharge to spec to eliminate both low charge or non condensable unknowns. So, is the fan not coming on at the right time? The computer may be taking into account your low ambient temp. A scanner is needed to evaluate and monitor all the computer commands to determine if everything is functioning properly or not. Its a high tech Mini BMW.


HECAT: You support the Forum when you consider for your a/c parts.


mikes603 on Tue April 28, 2015 9:55 AM User is offline

Well, having looked at manifolds setup on other Minis the HIGH side is much more stable. 100psi fluctuation seems like a Fan seems to be coming on at the right time.

Additionally, someone (I just got this car) had the clutch coil unplugged. As if to render the AC system inoperable. And at times the engine seems to bog down from the compressor load.

I'll be doing an evacuation and recharge this weekend if time permits. I just wanted to get some feedback on this 100psi HIGH side fluctuation going into it.

mk378 on Tue April 28, 2015 10:44 AM User is offline

The high side will go up and up until the computer decides to turn the fan on, so you really can't tell anything from pressures with the fan off. 150 with the fan on seems OK, but if the system is undercharged it is likely to keep going lower had the computer not turned the fan off.

Charge by weight is an essential first step on any modern system and the only way to be sure the charge is right.

Edited: Tue April 28, 2015 at 10:47 AM by mk378

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