How's the charge looking on this custom system?

[andrew vanis]

How's the charge looking on this custom system?

This vehicle application and installation viewtopic.php?t=14872

VW Vanagon
FS10 compressor
18x24 parallel flow condenser
32k BTU Evap
R134a
Ambient 85-90deg Humidity aprox 60%

Wondering what there is to see in these results (pic below, pressures in PSI, temps in F) and raw data and interactive graph here where one can hover over the lines to see the data points
https://docs.google.com/spreadsheets/d/ ... sp=sharing

This data is after the most recent refrigerant add.

Air cooling through Evap is 25F down from ambient. I'm wondering about the small Subcool often under 10, around 0, sometimes even negative. Also the high pressure looks low.

Do you see any other items to look at?
What additional info would be helpful?

So finally it is above 80deg in FL (coldest winter in a long time).

In Nov I pre-charged the system with about 70% of calculated expected capacity before heading to FL. Unfortunately a computer crash lost the refrigerant oz put in at that time (will try to recover).

I wanted to try the plateau method (which I admit I still don't really understand) but the evap drop was a consistent 25 deg and the sub-cool was up and down.

I added more refrigerant (about a can) but before adding it, during the addition, and after the addition i have the same 25deg diff between ambient and evap air temp out. All doors open, max fan, max cold, rad fan on stage 1. During the additional fill the compressor out fitting started to leak for about 20 seconds so I lost an unknown amount of charge and oil until it got tightened.

I'm wondering if these results indicate I should be adding more refrigerant or if there is anything else to see in them.

Thanks in advance for your help.

2024-4-26 AC chart w notes.jpg (62.61 KiB) Viewed 1623 times

[andrew vanis]

Unfortunately a computer crash lost the refrigerant oz put in at that time (will try to recover).

Was able to recover the lost data – Initially put in

23.1oz 134a
11.5oz oil

Yesterday I put in 16.6 oz so total I have in so far:

39.7 oz 134a
11.5 oz oil (29% oil ratio)

Based on prior planning calculations here viewtopic.php?p=28288#p28288

The similar systems provided by bohica2xo

Model / oil oz / R134a oz / oil ratio
Expedition 13 62 21%
Excursion 14 68 21%
E350 Van 13 46 28%

With my initial oil charge of 11.5 oz oil I could get the following 134a volumes for the following oil ratios

Oil oz / 134a oz / oil ratio
11.5 40 28.75%
11.5 45 25.56%
11.5 50 23.00%
11.5 55 20.91%
11.5 60 19.17%

With low SubCooling typically indicating undercharge, and a target oil ratio of around 20-25% from original calculations targeting like 45 oz 134a, later today I’ll keep adding refrigerant to the 39.7* oz in there now and see how it goes.

* an estimate due to the leak that occurred during fill.

If there is anything else that jumps out for the more experienced folks here please let me know.

[JohnHere]

I'm not surprised that you haven't received any replies to your latest posts.

You seem to want to get deeply involved in refrigeration science and system-design, and that's fine. But I would hazard a guess that more than 99-percent of this Forum's members simply don't have the background for such a discussion. In addition, automotive pros typically don't deal with superheat and subcooling. Home and commercial HVAC systems, yes. But in MVAC systems, it's not normally talked about for various reasons.

Why not try charging your unknown-capacity system the old-fashioned way: By adding refrigerant, a little at a time, while watching the pressures and center vent temperatures? If either or both start rising at some point, you've just passed the refrigerant-charge sweet spot for your system. You should then stop charging, make a note of how much refrigerant you put into the system for future reference, and call it a day.

The scientific material and complex charts that you seem determined to dwell on are probably far beyond the scope-of-knowledge of most people on this Forum, as I mentioned. Refrigeration science and system engineering are thoroughly covered in advanced HVAC classes should you wish to enroll in them.

[andrew vanis]

JohnHere, Thank you for your reply.. Just got back from my trip and will be working more on this shortly. Would love to have a simple "old Fashioned" way to do it and have a couple questions on what you wrote. Will ask those once I can phrase them clearly. First I have to re-evacuate my system and get it ready for re-charge.

[JohnHere]

JohnHere, Thank you for your reply.. Just got back from my trip and will be working more on this shortly. Would love to have a simple "old Fashioned" way to do it and have a couple questions on what you wrote. Will ask those once I can phrase them clearly. First I have to re-evacuate my system and get it ready for re-charge.

Sounds good. Catch up with you later.