Determining charge by Discharge pressure and liquid temp?

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Determining charge by Discharge pressure and liquid temp?

Postby Z2TT » Fri Dec 18, 2015 4:54 pm

Hi Guys.

I recently came across an article by 4 Seasons, which I'm trying to make sense of.

I'll post a picture of the graph of interest :

Image

I can't understand how certain scenarios under this graph are possible.
If the liquid line temp is low, it says that the system is overcharged - how can that be? as that's normally the case of an undercharge.

On the other hand it's showing that a high liquid line temp would mean an undercharge?
I'm confused.

Most of the times in an undercharge I've had low discharge pressures, and in overcharge high liquid line temps, not lower ones as graph seems to indicate

I'm unsure if I'm analyzing the graph properly.

Cheers.
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Re: Determining charge by Discharge pressure and liquid temp

Postby Z2TT » Fri Dec 18, 2015 5:00 pm

Another graph where the service port is on the liquid line - comparing liquid line pressure to temperature.
I understand the concept but what the graph is trying to show is just confusing :

I can't understand how you can have lets say a very high liquid line PRESSURE such as 270, and yet to the touch have the line to be at 100F resulting from an undercharge - as Graph shows this is a possible scenario.

Perhaps one of you guys could give me an example of a real life situation which has occured.
The only way I thought of knowing of an undercharge was measuring superheat if possible.

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Re: Determining charge by Discharge pressure and liquid temp

Postby Tom Greenleaf » Fri Dec 18, 2015 5:31 pm

I need some learning on this on very new stuff now too.

Didn't have time but a Ford Escape (family owned) was or wasn't putting out cool air out of vents. Of course it worked fine in front of me so was confused why it would perform then not. I didn't have much time and don't know where they hid the X valve on the thing. Guess was low charge as high/low tubes from evap should be about the same temp by feel or better and were NOT the same but for the test of performance was blowing plenty cool for me. Ran out of time so not done yet on a 3 year old thing!

Outdoor temps never hit a real 70F again long enough as I find that as low of an ambient temp to trust readings up to way too cold if you found a problem, fixed it to know it worked!

Said - family vehicle. I'll just evac and fill to spec in Spring as it's nice out but now just 48F on December 18th which is nice for here but too cold for A/C for me anyway.

******************************************************
Never mind the graphs for a second. What vehicle exactly and what is the complaint?

Tom
MetroWest, Boston
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